比特派苹果|atoms
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2024-03-08 21:10:12
Atom | Definition, Structure, History, Examples, Diagram, & Facts | Britannica
Atom | Definition, Structure, History, Examples, Diagram, & Facts | Britannica
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atom
Table of Contents
atom
Table of Contents
Introduction & Top QuestionsAtomic modelBasic propertiesAtomic numberAtomic mass and isotopesThe electronCharge, mass, and spinOrbits and energy levelsElectron shellsAtomic bondsConductors and insulatorsMagnetic propertiesThe nucleusNuclear forcesNuclear shell modelRadioactive decayNuclear energyDevelopment of atomic theoryThe atomic philosophy of the early GreeksThe emergence of experimental scienceThe beginnings of modern atomic theoryExperimental foundation of atomic chemistryAtomic weights and the periodic tableKinetic theory of gasesStudies of the properties of atomsSize of atomsElectric properties of atomsLight and spectral linesDiscovery of electronsIdentification of positive ionsDiscovery of radioactivityModels of atomic structureRutherford’s nuclear modelMoseley’s X-ray studiesBohr’s shell modelThe laws of quantum mechanicsSchrödinger’s wave equationAntiparticles and the electron’s spinAdvances in nuclear and subatomic physicsStructure of the nucleusQuantum field theory and the standard model
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Facts You Should Know: The Periodic Table Quiz
Related Questions
How is the atomic number of an atom defined?
What is the periodic table?
Where does the periodic table come from?
Why does the periodic table split?
When are isotopes stable?
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UEN Digital Press with Pressbooks - The Structure of the Atom
Open Oregon Educational Resources - Elements and Atoms: The Building Blocks of Matter
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Live Science - What Is an Atom? Facts About the Building Blocks of the Universe
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External Websites
Khan Academy - Introduction to the atom
Space.com - Atoms: What are they and how do they build the elements?
UEN Digital Press with Pressbooks - The Structure of the Atom
Open Oregon Educational Resources - Elements and Atoms: The Building Blocks of Matter
Chemistry LibreTexts - The Atom
Live Science - What Is an Atom? Facts About the Building Blocks of the Universe
Britannica Websites
Articles from Britannica Encyclopedias for elementary and high school students.
atom - Children's Encyclopedia (Ages 8-11)
atom - Student Encyclopedia (Ages 11 and up)
Written by
James Trefil
Clarence J. Robinson Professor of Physics, George Mason University, Fairfax, Virginia. Author of Science Matters: Achieving Scientific Literacy; Other Worlds: The Solar System and Beyond; and Encyclopedia...
James Trefil,
George F. Bertsch
Professor of Physics, University of Washington, Seattle. Author of Oscillations in Finite Quantum Systems.
George F. Bertsch,
Sharon Bertsch McGrayne
Science writer. Author of Nobel Prize Women in Science, Prometheans in the Lab, The Theory That Would Not Die, and others.
Sharon Bertsch McGrayneSee All
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shell atomic model
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Category:
Science & Tech
Key People:
Ernest Rutherford
Niels Bohr
Lev Davidovich Landau
Steven Chu
William D. Phillips
(Show more)
Related Topics:
subatomic particle
radioactivity
isotope
atomism
periodic table
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Open Oregon Educational Resources - Elements and Atoms: The Building Blocks of Matter (Feb. 12, 2024)
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What is an atom?An atom is the basic building block of chemistry. It is the smallest unit into which matter can be divided without the release of electrically charged particles. It also is the smallest unit of matter that has the characteristic properties of a chemical element.Are all atoms the same size?All atoms are roughly the same size, whether they have 3 or 90 electrons. Approximately 50 million atoms of solid matter lined up in a row would measure 1 cm (0.4 inches). A convenient unit of length for measuring atomic sizes is the angstrom, defined as 10−10 meters.What does the mass of an atom consist of?The mass of an atom consists of the mass of the nucleus plus that of the electrons. That means the atomic mass unit is not exactly the same as the mass of the proton or neutron.How is the atomic number of an atom defined?The single most important characteristic of an atom is its atomic number (usually denoted by the letter Z), which is defined as the number of units of positive charge (protons) in the nucleus. For example, if an atom has a Z of 6, it is carbon, while a Z of 92 corresponds to uranium.atomsHow atoms can be seen.(more)See all videos for this articleatom, the basic building block of all matter and chemistry. Atoms can combine with other atoms to form molecules but cannot be divided into smaller parts by ordinary chemical processes.Explore an atom's interior to discover the layout of its nucleus, protons, and electronsSee all videos for this articleMost of the atom is empty space. The rest consists of three basic types of subatomic particles: protons, neutrons, and electrons. The protons and neutrons form the atom’s central nucleus. (The ordinary hydrogen atom is an exception; it contains one proton but no neutrons.) As their names suggest, protons have a positive electrical charge, while neutrons are electrically neutral—they carry no charge; overall, then, the nucleus has a positive charge. Circling the nucleus is a cloud of electrons, which are negatively charged. Like opposite ends of a magnet that attract one another, the negative electrons are attracted to a positive force, which binds them to the nucleus. The nucleus is small and dense compared with the electrons, which are the lightest charged particles in nature. The electrons circle the nucleus in orbital paths called shells, each of which holds only a certain number of electrons.Investigate varying electron configurations in electron shells around an atom's nucleusAtomic model of electron configurations.(more)See all videos for this articleAn ordinary, neutral atom has an equal number of protons (in the nucleus) and electrons (surrounding the nucleus). Thus the positive and negative charges are balanced. Some atoms, however, lose or gain electrons in chemical reactions or in collisions with other particles. Ordinary atoms that either gain or lose electrons are called ions. If a neutral atom loses an electron, it becomes a positive ion. If it gains an electron, it becomes a negative ion. These basic subatomic particles—protons, neutrons, and electrons—are themselves made up of smaller substances, such as quarks and leptons.More than 90 types of atoms exist in nature, and each kind of atom forms a different chemical element. Chemical elements are made up of only one type of atom—gold contains only gold atoms, and neon contains only neon atoms--and they are ranked in order of their atomic number (the total number of protons in its nucleus) in a chart called the periodic table. Accordingly, because an atom of iron has 26 protons in its nucleus, its atomic number is 26 and its ranking on the periodic table of chemical elements is 26. Because an ordinary atom has the same number of electrons as protons, an element’s atomic number also tells how many electrons its atoms have, and it is the number and arrangement of the electrons in their orbiting shells that determines how one atom interacts with another. The key shell is the outermost one, called the valence shell. If this outermost shell is complete, or filled with the maximum number of electrons for that shell, the atom is stable, with little or no tendency to interact with other atoms. But atoms with incomplete outer shells seek to fill or to empty such shells by gaining or losing electrons or by sharing electrons with other atoms. This is the basis of an atom’s chemical activity. Atoms that have the same number of electrons in the outer shell have similar chemical properties.
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This article opens with a broad overview of the fundamental properties of the atom and its constituent particles and forces. Following this overview is a historical survey of the most influential concepts about the atom that have been formulated through the centuries. Atomic model Most matter consists of an agglomeration of molecules, which can be separated relatively easily. Molecules, in turn, are composed of atoms joined by chemical bonds that are more difficult to break. Each individual atom consists of smaller particles—namely, electrons and nuclei. These particles are electrically charged, and the electric forces on the charge are responsible for holding the atom together. Attempts to separate these smaller constituent particles require ever-increasing amounts of energy and result in the creation of new subatomic particles, many of which are charged.
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As noted in the introduction to this article, an atom consists largely of empty space. The nucleus is the positively charged centre of an atom and contains most of its mass. It is composed of protons, which have a positive charge, and neutrons, which have no charge. Protons, neutrons, and the electrons surrounding them are long-lived particles present in all ordinary, naturally occurring atoms. Other subatomic particles may be found in association with these three types of particles. They can be created only with the addition of enormous amounts of energy, however, and are very short-lived. All atoms are roughly the same size, whether they have 3 or 90 electrons. Approximately 50 million atoms of solid matter lined up in a row would measure 1 cm (0.4 inch). A convenient unit of length for measuring atomic sizes is the angstrom (Å), defined as 10−10 metre. The radius of an atom measures 1–2 Å. Compared with the overall size of the atom, the nucleus is even more minute. It is in the same proportion to the atom as a marble is to a football field. In volume the nucleus takes up only 10−14 metres of the space in the atom—i.e., 1 part in 100,000. A convenient unit of length for measuring nuclear sizes is the femtometre (fm), which equals 10−15 metre. The diameter of a nucleus depends on the number of particles it contains and ranges from about 4 fm for a light nucleus such as carbon to 15 fm for a heavy nucleus such as lead. In spite of the small size of the nucleus, virtually all the mass of the atom is concentrated there. The protons are massive, positively charged particles, whereas the neutrons have no charge and are slightly more massive than the protons. The fact that nuclei can have anywhere from 1 to nearly 300 protons and neutrons accounts for their wide variation in mass. The lightest nucleus, that of hydrogen, is 1,836 times more massive than an electron, while heavy nuclei are nearly 500,000 times more massive.
Basic properties Atomic number The single most important characteristic of an atom is its atomic number (usually denoted by the letter Z), which is defined as the number of units of positive charge (protons) in the nucleus. For example, if an atom has a Z of 6, it is carbon, while a Z of 92 corresponds to uranium. A neutral atom has an equal number of protons and electrons so that the positive and negative charges exactly balance. Since it is the electrons that determine how one atom interacts with another, in the end it is the number of protons in the nucleus that determines the chemical properties of an atom.
杜比atmos与杜比7.1或者5.1的区别？ - 知乎
杜比atmos与杜比7.1或者5.1的区别？ - 知乎首页知乎知学堂发现等你来答切换模式登录/注册杜比全景声杜比atmos与杜比7.1或者5.1的区别？Q1：杜比atmos是不是不用考虑扬声器的数量，哪是就算扬声器的数量很少也能听到全景声？ Q2：atoms是不是相对于7.1或5.1在音频处理上做了优…显示全部 关注者30被浏览91,460关注问题写回答邀请回答好问题 4添加评论分享7 个回答默认排序SaerXZ您说得对 关注最近正好针对这种技术，包括DTS:X和Auro-3D这两个类似的系统查了很多东西，这里总结一下，相信能够比较好地回答清楚这个问题。Q1: 这是Atmos与传统5.1和7.1的一个重要区别：它的扬声器配置是非常灵活的，因为在最终输出之前，在AVR(家用)或者DSP(商用)内部会针对当前的配置进行不一样的输出。理论上来说只要你的系统在5.1.2以上都是OK的。当然了，扬声器越多效果越好，最大应该是有9.2.6。Q2: 当然是有很大区别的，但是它是针对传统5.1和7.1的扩充，软件和硬件上都是的。Dolby Atmos，DTS:X，Auro-3D，它们三个有一个共同的名字，叫做Object-based Audio。传统的5.1，7.1，包括现在正在研发中的22.2，都是Channel-based Audio。什么意思呢？Channel-based，顾名思义，是基于每一个声道进行处理的技术。从5.1时代开始，要么就是录制的时候使用多组麦克风来录制，要么就是在后期制作中将部分效果音和环境音做一些环绕效果。比如说像Nuendo这种软件里面会有Surround Panner，你可以对一个环境音指定在平面上的位置，比如在前方占25%，在后方75%，从左到右做一个移动这样的指令，然后软件就会进行相应的混音处理。这样的弊端是显而易见的，它的实际效果很大程度上受回放设备的制约，制作的时候也无法把定位效果做得非常精确，如果要达到很好的效果还是要实际收音的。所以传统的5.1和7.1音轨实际听起来大多是提供一个“环绕效果”，比如“后面发生了爆炸”“右后方飞过来一架飞机”，很少会提供一个精准的结像。现在最新的22.2技术，NHK专门做了一个球状的设备，上面捆了22个麦克风来收音，这样做的DEMO效果还可以，但是说实话怎么看怎么蠢对吧……更何况现在的很多电影大部分都是后期制作，上哪去收音呢？那么Object-based呢，其实也有5.1和7.1的东西在里面。首先针对氛围和临场感，使用传统的5.1和7.1的音轨，具体的定位效果则是通过指定对象实现的，比如Atmos没记错的话同时最大可以指定118个对象。在制作的时候，是将效果音绑定在对象上，然后指定其三维坐标，将这些数据（而不是混音之后的结果）藏在7.1的音轨里（所以不支持Atmos的设备播放Atmos音轨的时候只能解码7.1TrueHD），如果设备支持Atmos就读取这些数据进行渲染（家用是AVR，商用一个是制作的时候用Dolby的RMU，相当于一个专用渲染服务器，还有一个是电影院会配Dolby的DSP，官网上现在用的型号是CP850），渲染之前只要在设备里指定现在的扬声器配置就OK了。这样的实时处理就可以保证实际输出的时候是根据你的扬声器配置来的，一切计算全部交给回放设备，最大程度地减小扬声器配置对实际效果的影响，从而实现精确的空间定位。这个也决定了普通的电脑软件没有Dolby授权是做不了Atmos解码的，因为你必须知道它对对象数据的定义和具体处理算法才能写出解码器。反之，只要你能原原本本地输出源码音频，不管你的数字播放设备是什么，解码接收到的信号里面包括这些对象信息就可以作为Atmos处理。Object-based还有一个好处，就是可以通过后期追加对象信息，将以前采用传统方式制作的电影，配合4K重制技术发行新的版本。使用当时制作电影时留下的音频素材，就可以在重制的时候追加对象信息，做出Atmos音轨了。这也是为什么演唱会音乐会大多没有Atmos版，因为不需要做这样的效果，在现场收音的时候使用7.1或者5.1系统收音就可以了。所以像敦刻尔克这样的电影也没有必要做Atmos版（实际上敦刻尔克的UHD BD确实只有7.1音轨），科幻片动作片则是重制了不少Atmos版本。发布于 2018-05-25 11:47赞同 328 条评论分享收藏喜欢收起飞龙在天音频工程师 关注Q1:实际上是要考虑扬声器的数量的，要听全景声，至少5.1.2个声道，有厂家把几个声道用反射技术做成一个或几个扬声器，但是每个声道至少要一个喇叭发出声音。在制作atmos的时候也需要考虑扬声器数量，对于氛围和临场感的声场，杜比把它称为”sound bed“目前是用的5.1.2或者7.1.2的格式来制作的。而object则是在这个格式里去定义它的位置及移动速度等等，再通过渲染器去渲染成其它的格式比如电影院里的22.2,9.1.6,5.1.4,7.1.4等等。Q2：目前所有的三维声都是基于声道的，因为最终需要扬声器矩阵来重放，每个扬声器重放一个声道，多个扬声器实现半球形的声场。只是在制作的时候用object这种方式可以高效的做成不同的声道格式目前，网上能找到的全景声的蓝光高清的影片基本上都是5.1.2（也就是标的atmos 7.1）格式的，所以家庭用最好的重放方式是5.1.2的扬声器布局编辑于 2018-12-29 20:38赞同 72 条评论分享收藏喜欢
什么是杜比全景声（Dolby Atmos） - 知乎
什么是杜比全景声（Dolby Atmos） - 知乎首发于音视频系统全形态解决方案切换模式写文章登录/注册什么是杜比全景声（Dolby Atmos）涡轮猫设计师 杜比全景声（Dolby Atmos）是杜比实验室于2012年推出的高级环绕声标准，用于电影院，通过将前置、侧置、后置和天空扬声器加上复杂的音频处理和算法相结合，提供高达最高64声道的环绕声，增加空间沉浸感。杜比全景声（Dolby Atmos）的目的是在商业电影环境中提供完整的声音沉浸体验。继电影院（2012-2014）取得初步成功之后，杜比与多家AV功放和扬声器制造商合作，将杜比全景声（Dolby Atmos）体验融入到家庭影院场景中。当然，只有具有一定消费能力或非常钟爱于音视频系统的家庭可以负担得起安装在商业环境中使用的相同类型的杜比全景声（Dolby Atmos）系统所需的功能，因此杜比实验室为制造商提供了更合适的物理缩小版本（并且价格合理） ）对消费者进行必要的升级以在家中享受杜比全景声（Dolby Atmos）体验。那么，如何在不受影响的情况下拥有纯正杜比全景声（Dolby Atmos）呢？杜比全景声基础知例如DENON 6400杜比全景声家庭影院功放。7.2.4全景声功放、DTS-X Auro3D 11.2声道具备Denon顶级AV机型的技术11个声道俱各提供210瓦的功率，您可以添加更广泛的前置声场，而Audyssey DSX可以深度调整至最佳声场 -当一些特定声场时，你可能不会遇到连续的环绕音效。但是，杜比全景声（Dolby Atmos）可以填补这些环绕声音效。空间编码：杜比全景声技术的核心是空间编码（不要与MPEG空间音频编码混淆），声音信号被分配到空间中的位置而不是特定的通道或扬声器。在播放影片时，包含在内容中的比特流编码的元数据（例如蓝光光盘电影）由家庭影院功放或前级AV处理器中的杜比全景声处理芯片在运行中解码，这使得声音信号空间分配基于在播放设备的频道/设置上（称为播放渲染器 ）。设置：要为您的家庭影院设置最佳的Dolby Atmos聆听选项（假设您使用的是支持Dolby Atmos的家庭影院功放或前级AV处理器/合并机），菜单系统将询问您以下问题：有多少扬声器你有？你的影视厅有多大？你的扬声器在哪里？均衡器和室内校正系统：到目前为止，杜比全景声（Dolby Atmos）与现有的自动扬声器设置/均衡/室内校正系统兼容，如Audyssey，MCACC，YPAO等......体验天空声：天空声通道是杜比全景声（Dolby Atmos）体验中不可或缺的一部分。要体验天空声通道，您可以在天花板上安装扬声器。所有扬声器连接复杂性的最终解决方案可能只是有源无线扬声器，但是这个方案只能在以后能解决，因为在这之前，并没有无线支持Dolby Atmos的扬声器可用。新的声轨配置：过往我们熟悉的描述声轨配置的方法，诸如5.1、7.1、9.1等.....而现在你会看到5.1.2、7.1.2、7.1.4、9.1.4等等的描述......扬声器放在一个水平面上（左/右前面和环绕声）是第一个数字，超低音扬声器（低音炮）是第二个数字（可能是.1或.2），天花板安装代表最后一个数字（通常为.2或.4）硬件和内容可用性： 蓝光光盘上的杜比全景声（Dolby Atmos）编码内容可用。杜比全景声（Dolby Atmos）的播放器兼容当前的蓝光和超高清蓝光光盘格式标准。可以向后兼容几乎所有蓝光光盘播放器。但是，要体验Dolby Atmos音轨，蓝光播放器必须具有HDMI 1.3（或更新） 输出，并且必须关闭播放器的辅助音频输出设置（辅助音频通常是导演评论之类的内容）。当然，必须使用支持杜比全景声（Dolby Atmos）的家庭影院功放或前级AV处理器作为解码的一部分。Dolby TrueHD和Dolby Digital Plus： Dolby Atmos标准适用于Dolby TrueHD和Dolby Digital Plus格式。有意思是，由于杜比全景声（Dolby Atmos）可以嵌入杜比数字+（Dolby Digital Plus）结构中，因此您可能会看到杜比全景声（Dolby Atmos）在流媒体（爱奇艺客户端等APP）和智能移动设备（三星 Galaxy S9手机）中的应用。对消费者的价值： 超越此前所有技术标准，从我一直使用杜比全景声（Dolby Atmos）的经验来看，它是家庭影院音频的颠覆者。从录音和混音开始，到最终的聆听体验，杜比全景声（Dolby Atmos）虽然仍然需要扬声器和功放来重现声音，但是从各扬声器中发出的声音，这种沉浸式的环绕声体验式史无前例的！从飞越头顶的鸟类或直升机，到从上方落下的雨水，到任何方向的雷声，杜比全景声（Dolby Atmos）能给你带来高度准确的沉浸式聆听体验。发布于 2018-11-03 14:23杜比环绕声杜比全景声赞同 3611 条评论分享喜欢收藏申请转载文章被以下专栏收录音视频系统全形态解决方案这里的内容也许可以帮你提升一定的生活品质智趣科技数码测评智能有趣的科技数码产
Atoms - What are they? What's inside them? - Explain that Stuff
Atoms - What are they? What's inside them? - Explain that Stuff
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Atoms
Atoms
by Chris Woodford. Last updated: January 24, 2024.
Suppose you had to
build yourself a world exactly like the one we live in. Where would
you start? You'd need people... cars... houses... animals... trees...
and billions of other things. But if you had a few dozen different
types of atom, you could build all these things and more: you'd just
join the atoms together in different ways. Atoms are the tiny
building blocks from which everything around us is constructed. It's
amazing to think you can make anything out of atoms, from a snake to
an ocean liner—but it's absolutely true! Let's take a closer
look.
Artwork: From the hair on your head to the t-shirt on your back, everything in the world is made of atoms.
I've greatly exaggerated their size in this illustration. On my screen, each of the atomic red dots
is about 10 million times bigger than a typical atom.
(Your screen may be bigger or smaller than mine, or scaled differently, so
take that as a very rough approximation.)
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Contents
What is an atom?
What are the parts of an atom?
What is the Periodic Table?
How do atoms make molecules and compounds?
What are isotopes?
How do atoms make ions?
How many atoms are there in something?
How do we know atoms exist?
A brief history of atoms
Find out more
What is an atom?
Take anything apart and
you'll find something smaller inside. There are engines inside cars,
pips inside apples, hearts and lungs inside people, and stuffing
inside teddy bears. But what happens if you keep going? If you keep
taking things apart, you'll eventually, find that all matter
(all the "stuff" that surrounds us) is made from
different types
of atoms. Living things, for example, are mostly made from the atoms
carbon, hydrogen, and oxygen. These are just three of over 100
chemical elements that scientists have
discovered. Other
elements include metals such as copper, tin, iron and
gold, and gases
like hydrogen and helium. You can make virtually anything you can
think of by joining atoms of different elements together like tiny
LEGO®
blocks.
Photo: What does an atom look like? You can see one if you have the
right kind of microscope or camera! This photo shows strontium atoms
"flying" in a cube while being stimulated with precision laser light.
By courtesy of National Institute of Standards and Technology (NIST).
An atom is the smallest
possible amount of a chemical element—so an atom of gold is the
smallest amount of gold you can possibly have. By small, I really do
mean absolutely, nanoscopically
tiny: a single atom is
hundreds of thousands of times thinner than a human hair, so you have absolutely no
chance of ever seeing one unless you have an incredibly powerful
electron microscope. In ancient
times, people thought atoms
were the smallest possible things in the world. In fact, the word
atom comes from a Greek word meaning something that cannot be split
up any further. Today, we know this isn't true. In theory, if you had a knife
small and sharp enough, you could chop an atom of gold into bits and you'd
find smaller things inside. But then you'd no longer have the gold:
you'd just have the bits. All atoms are made from the same bits,
which are called subatomic particles ("sub"
means smaller than and these are particles smaller than atoms). So if you chopped
up an atom of iron, and put the bits into a pile, and then chopped up
an atom of gold, and put those bits into a second pile, you'd have
two piles of very similar bits—but there'd be no iron or gold
left.
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What are the parts of an atom?
Most atoms have three
different subatomic particles inside them: protons,
neutrons,
and electrons. The protons and neutrons are
packed together
into the center of the atom (which is called the nucleus)
and the electrons, which are very much smaller, whizz around the
outside. When people draw pictures of atoms, they show the electrons
like satellites spinning round the Earth in orbits. In fact,
electrons move so quickly that we never know exactly where they are
from one moment to the next. Imagine them as super-fast racing cars
moving so incredibly quickly that they turn into blurry
clouds—they
almost seem to be everywhere at once. That's why you'll see some
books drawing electrons inside fuzzy areas called orbitals.
Artwork: Atoms contain protons and neutrons packed into the central area called the nucleus, while
electrons occupy the space around it. In simple descriptions of the atom, we often talk about electrons "orbiting" the nucleus like
planets going around the Sun or satellites whizzing around Earth, although that's a
huge oversimplification.
Note also that this picture isn't drawn to scale! Most of an atom is empty space. If an atom were about as big as a baseball stadium, the nucleus would be the size of a pea in the very center and the electrons would be somewhere on the outside edge.
What makes an atom of gold different from an atom of iron is the number of protons,
neutrons, and electrons inside it. Cut apart a single atom of iron
and you will find 26 protons and 30 neutrons clumped together in the
nucleus and 26 electrons whizzing around the outside. An atom of gold
is bigger and heavier. Split it open and you'll find 79 protons and
118 neutrons in the nucleus and 79 electrons spinning round the edge.
The protons, neutrons, and electrons in the atoms of iron and gold are
identical—there are just different numbers of them. In theory,
you could turn iron into gold by taking iron atoms and adding 53 protons,
88 neutrons, and 53 electrons to each one. But if that were as easy as
it sounds, you can bet all the world's chemists would be very rich
indeed!
But let's suppose you
could turn atoms into other atoms very simply. How would you make the
first few chemical elements? You'd start with the simplest atom of all,
hydrogen (symbol H), which has one proton and one electron, but no
neutrons. If
you add another proton, another electron, and two neutrons, you get
an atom of helium (symbol He). Add a further proton, another electron,
and two
more neutrons, and you'll have an atom of the metal lithium (symbol
Li). Add one proton, one neutron, and one electron and you get an atom
of beryllium (symbol Be).
See how
it works? In all atoms, the number of protons and the number of
electrons is always the same. So nitrogen has 7 protons and 7 electrons,
calcium has 20 protons and 20 electrons, and tin has 50 protons and
50 electrons.
The number of neutrons is very roughly the
same as the number of protons, but sometimes it's rather more.
So bromine has 35 protons and 35 electrons, but 45 neutrons.
Platinum has 78 protons, 78 electrons, and 117 neutrons.
The number of protons in an atom is called the
atomic number and it tells you what type of atom you have. An atomic number of 1
means the atom is hydrogen, atomic number 2 means helium, 3 means
lithium, 4 is beryllium, and so on. The total number of protons and
neutrons added together is called the relative atomic mass.
Hydrogen has a relative atomic mass of 1, while helium's relative
atomic mass is 4 (because there are two protons and two neutrons
inside). In other words, an atom of helium is four times heavier than
an atom of hydrogen, while an atom of beryllium is nine times heavier.
What is the Periodic Table?
Suppose you make a list of the chemical elements in order of their atomic number (how many protons they have), starting with hydrogen (H). You'll find that elements with similar chemical properties (how they react with things) and physical properties (whether they're metals or non-metals, how they conduct heat and electricity, and so on) occur at regular intervals—periodically, in other words. If you rearrange your list into a table so similar atoms fall underneath one another, you get a diagram like this, which is called the Periodic Table. The columns are called groups and the rows are called periods.
Artwork: The Periodic Table of the elements.
So what? Atoms in a certain group (column) tend to have similar properties. So, for example, the red column on the right contains the Noble Gases (helium, neon, argon, krypton, and so on), which are relatively unreactive. The pink column on the left contains the alkali metals (lithium, sodium, potassium, and so on), which are relatively reactive metals (you probably know that some of them react violently with water, for example, to produce explosive hydrogen gas). If you know where a certain element sits in the table, and you know a little bit about the properties of the elements above, below, and either side, you can often figure out what the properties of that element will be.
How do atoms make molecules and compounds?
Atoms are a bit like
people: they usually prefer company to being alone. A lot of atoms
prefer to join up with other atoms because they're more stable that
way. So hydrogen atoms don't exist by themselves: instead, they pair
up to make what is called a molecule of
hydrogen. A molecule
is the smallest amount of a compound: a
substance made from two or more atoms.
Some people find molecules and compounds confusing. Here's how to
remember the difference. If you join two
different chemical elements together, you can often make a completely
new substance. Glue two atoms of hydrogen to
an atom of oxygen and you'll make a single molecule of water.
Water is a compound (because it's two different chemical elements joined
together), but it's also a molecule because it's made by combining
atoms. The way to remember it is like this: compounds are elements
joined together and molecules are atoms joined together.
Not all molecules are as small and simple as water. Molecules of
plastics, for example, can be made of hundreds or even thousands of individual
atoms joined together in incredibly long chains called polymers.
Polythene (also called polyethene or polyethylene) is a very simple example of this.
It's a polymer made by repeating a basic unit called a monomer
over and over again—just like a coal train made by coupling together any number of identical trucks,
one after another:
What are isotopes?
To complicate things a
bit more, we sometimes find atoms of a chemical element that are a
bit different to what we expect. Take carbon, for example. The
ordinary carbon we find in the world around us is sometimes called
carbon-12. It has six protons, six electrons, and six neutrons, so
its atomic number is 6 and its relative atomic mass is 12. But
there's also another form of carbon called carbon-14, with six
protons, six electrons, and eight neutrons. It still has an atomic
number of six, but its relative atomic mass is 14. Carbon-14 is more
unstable than carbon-12, so it's radioactive:
it naturally
disintegrates, giving off subatomic particles in the process, to turn
itself into nitrogen. Carbon-12 and carbon-14 are called
isotopes of carbon. An isotope is simply an atom with a different number of
neutrons that we'd normally expect to find.
Artwork: Carbon-12 and carbon-14 are both isotopes of carbon: different
variations that have different numbers of neutrons (blue). Carbon-14 has two more neutrons (yellow) than carbon-12, but both have six protons (red) and six electrons (green).
How do atoms make ions?
Atoms aren't just packets of matter: they contain electrical energy too. Each proton in
the nucleus of an atom has a tiny positive charge (electricity that stays in
one place).
We say it has a charge of +1 to make everything simple
(in reality, a proton's charge is a long and complex number: +0.00000000000000000016021892 C, to be
exact!). Neutrons have no charge at all.
That means the nucleus of an atom is effectively a big clump of
positive charge.
An electron is tiny compared to a proton, but it has exactly the same
amount of charge. In fact, electrons have an opposite charge to
protons (a charge of −1 or −0.00000000000000000016021892 C, to be
absolutely exact). So protons and electrons are a bit like the
two different ends of a battery: they have equal and opposite
electric charges. Since an atom contains equal number of protons and
electrons, it has no overall charge: the positive charges on all the
protons are exactly balanced by the negative charges on all the
electrons. But sometimes an atom can gain or lose an electron to
become what's called an ion. If it gains an
electron, it has
slightly too much negative charge and we call it a negative ion; it
it loses an electron, it becomes a positive ion.
Artwork: A lithium atom (Li) forms a positive ion (Li +) by "losing" an electron. A fluorine atom (F) forms a negative ion (F −) by gaining an electron.
What's so good about
ions? They're very important in many chemical reactions. For
example, ordinary table salt (which has the chemical name sodium
chloride) is made when ions of sodium join together with ions made
from chlorine (which are called chloride ions). A sodium ion is made
when a sodium atom loses an
electron and becomes positively charged. A chloride ion forms in the
opposite way when a chlorine atom gains an electron to become
negatively charged. Just like two opposite magnet poles, positive and
negative charges attract one another. So each positively charged
sodium ion snaps onto a negatively charged chloride ion to form a
single molecule of sodium chloride. When compounds form through two
or more ions joining together, we call it
ionic bonding. Most metals form their compounds in this way.
The electrical charge that ions have can be useful in all sorts of ways. Ions (as well as
electrons) help to carry the electricity through
batteries when you connect them into a circuit.
How many atoms are there in something?
If atoms are so tiny, there must be zillions and zillions of them in all the things around
us... but how many are there, exactly?
Chemists have a handy way of talking amount these vast numbers of atoms—by using the
rather unusual word mole.
A mole of something (anything) has exactly 6.022 × 1023 particles in it,
which is a short way of saying 602,200,000,000,000,000,000,000 or 602 billion trillion.
This strange amount is called Avogadro's number (or Avogadro's constant)
after Italian chemist Amedeo Avogadro (1776–1856), who thought up the idea.
Avogadro's original hypothesis was that a certain volume of any gas will contain the same number of molecules
as the same volume of any other gas providing both gases are at the same temperature and pressure.
So how much is a mole? When we're talking about atoms, a mole is
the relative atomic mass in grams. So a mole of carbon is 12g, because carbon's
relative atomic mass is 12, and it contains 620 billion trillion atoms.
A mole of aluminum is 27g, because aluminum's relative atomic mass is 27.
A mole of aluminum also contains 620 billion trillion atoms.
We can also use moles to talk about molecules. A mole of a compound
contains 602 billion trillion molecules. A molecule of water has a relative molecular mass of 18 (that's
16 for the oxygen atom, plus two hydrogens, making 18).
A mole of water weighs 18g and contains 620 billion trillion molecules.
Photo: A mole of any substance contains the same number of elementary
particles (atoms, molecules, ions, electrons, or anything else). Here you can see 18g of water,
12g of carbon, 63g of copper, and 27g of aluminum. Each of these is a mole and contains 602 billion
trillion atoms (or molecules, in the case of water). Photo courtesy of
National Institute of Standards and Technology Digital Collections, Gaithersburg, MD 20899.
How do we know atoms exist?
Artwork: Molecules are built from atoms: In the early 19th century, English chemist John Dalton (1766–1844) realized that atoms join together in simple
ratios. Water forms when two hydrogens snap onto one oxygen. Chemical reactions like this
make sense if the elements exist as simple building blocks: atoms, in other words.
If we can't see atoms, how do we know they're there? That's a very good question!
Science is all about evidence, so what evidence do we have that atoms really exist?
It comes in a variety of different forms:
Chemists have long known that when we combine different elements in chemical reactions,
the ingredients join in simple ratios. So, for example, in water we know that there
are twice as many hydrogen atoms as oxygen atoms (H2O), making
a ratio of 2:1. In salt (sodium chloride) there are equal numbers of sodium and chlorine atoms (NaCl),
so the ratio is 1:1. We can easily explain this if chemical elements really exist as
simple particles (atoms, in other words), which snap together like building blocks.
Some substances are radioactive: they naturally split into simpler substances and give off tiny
particles or energy in the process. Again, this makes sense if atoms exist and they're built
from smaller particles (protons, neutrons, and electrons).
Scientists can split big atoms into smaller ones. In one very
famous series of experiments in the early 20th century, a team led by
Ernest Rutherford (a New-Zealand-born physicist) fired particles at atoms and watched what happened. This showed how the bits were arranged inside a typical atom (with the nucleus at the center).
We have plenty of evidence for tiny particles called electrons: they
power things like electricity and magnetism.
An English physicist named J.J. Thomson
discovered electrons in 1897. This
discovery helped scientists to realize that atoms are made of even smaller bits.
Unlike these earlier scientists, we can actually see atoms; just look at the photo of sulfur atoms up above!
Seeing that picture would have delighted Rutherford, Thomson, and the other pioneers of atomic science.
Now, scientists are even starting to see inside atoms. Thanks to the development of really powerful
electron microscopes, we can peer deep inside things at
their internal atomic structure. In 2013, for example, scientists used a quantum
microscope to produce the first picture of the inside of a hydrogen atom. Amazing!
There's plenty more evidence where that came from, but this will do for starters. It shows us that our theory of what atoms
are and how they are built is a very good one: the theory agrees with the things we see around us in the world and it's
confirmed by many different kinds of evidence. It's not a complete theory, however: we still have an enormous amount to learn
about atoms and the bits and pieces lurking inside them!
A brief history of atoms
Who discovered the atom, how, and when? Let's quickly nip back through history...
450 BCE: Ancient Greek philosophers Leucippus and Democritus became the first people to propose that matter is made of atoms.
1661: Anglo-Irish chemist Robert Boyle (1627–1691) suggested that chemical elements were the simplest forms of matter.
1789: Frenchman Antoine Lavoisier (1743–1794), widely known as the "father of modern chemistry," set out a list of chemical elements (which he defined as substances that can't be broken down through a chemical reaction). This was an important stepping stone on the way to the full Periodic Table.
1803: English scientist John Dalton (1766–1844) published the atomic theory of matter. He realized each chemical element was made up of atoms.
1815: English physician William Prout (1785–1850) suggested the weights of different elements are simple multiples of the weight of a hydrogen atom—not quite true, but another important clue to understanding
how atoms are made.
1869: Building on the insights of Lavoisier, Dalton, Prout and others, a Russian chemist called Dmitri Mendeleyev (1834–1907) found a logical way of organizing the chemical elements with a neat structure called the Periodic Table.
1896: French physicist Henri Becquerel (1852–1908) accidentally discovered radioactivity.
1917: New Zealand-born English physicist Ernest Rutherford (1871–1937) "split" the atom: he proved that atoms are made of smaller particles, eventually concluding they had a heavy, positively charged nucleus and a largely empty area around them.
1919: British physicist Francis Aston (1852–1908) discovered a large number of
atomic isotopes using mass spectrometry.
1938: German physicists Otto Hahn (1879–1978)
and Fritz Strassmann (1902–1980) achieved the first nuclear fission
(splitting up of heavy atoms to make lighter ones).
1945: The United States dropped atomic bombs on the Japanese cities of Hiroshima and Nagasaki.
1960s–1970s: Particle physicists figured out how several fundamental forces hold small, "subatomic" particles together
to make atoms. Their ideas gradually became known as the Standard Model.
2013: Scientists used a quantum microscope to take the first pictures inside a hydrogen atom.
Sponsored links
Find out more
On this website
Electron microscopes
Materials
Nanotechnology
Solids, liquids, and gases
On other sites
The Particle Adventure: One of the best simple websites explaining atoms and the world inside them.
Structure of Matter: This very good interactive slideshow from the Nobel Prize website explains, in 22 slides, all about atoms and the other particles inside them. [Archived via the Wayback Machine.]
Dark matter and dark energy: Most of the "stuff" in the universe isn't conventional matter or energy, as we've always conceived it: it's actually "dark matter" and "dark energy." This NASA website explains what these things are and how they relate to conventional matter and energy.
Articles
Ultrasensitive Microscope Reveals How Charging Changes Molecular Structures by Dexter Johnson, IEEE Spectrum, July 11, 2019. What happens to the structure of molecules when they gain or lose electric charges?
Scientists Took an M.R.I. Scan of an Atom by Knvul Sheikh, The New York Times, July 1, 2019. Scientists from IBM Almaden and the Institute for Basic Sciences in Seoul discover what happens when you look at atoms in a body scanner.
Do Not Adjust Focus. Those Blobs Are Atoms by Kenneth Chang, The New York Times, October 5, 2004. The quest to take pictures of an atom continues!
Books for younger readers
Can you feel the force? by Richard Hammond. Dorling Kindersley, 2015. Includes a short introduction to atoms, quantum theory, and particle physics.
The Periodic Table by Adrian Dingle.
Oxford University Press, 2014.
Atoms and Molecules by Chris Woodford and Martin Clowes. Rosen, 2012. (Previously published by Blackbirch.) One of my own books, this charts the history of atomic theory from ancient times to modern.
Splitting the Atom by Alan Morton. Evans, 2005.A brief history of atom theory.
How to split the atom by Hazel Richardson. Oxford University Press, 1999. A zany, fun guide that will appeal to lovers of the Horrible Science series.
Eyewitness: Matter by Christopher Cooper.
Dorling Kindersley, 1992. A drier, but solid introduction; good for school projects.
Books for older readers
Atom by Piers Bizony. Icon, 2017. The story of how scientists came to understand atoms.
The Elements: A Visual Exploration of Every Known Atom in the Universe by Theodore Gray. Black Dog & Leventhal, 2012. An entertaining trip through the Periodic Table.
Mr. Tompkins in Paperback by George Gamov. Cambridge, 2012. A very vivid introduction to the world inside atoms from one of the 20th-century's most creative physicists. Suitable for older teens and above.
The Fly in the Cathedral by Brian Cathcart. Farrar, Straus and Giroux, 2005. Excellent, easy-to-understand account of how Ernest Rutherford and his team figured out the structure of atoms. Also published in paperback
by Penguin.
Six Easy Pieces by Richard Feynman. Penguin, 1998. This book is by no means as "easy" as its title suggests, but the final chapter does contain a pithy explanation of quantum theory and its various puzzles that people with a basic grounding in physics can hope to understand.
Videos
What is a Higgs boson?: Don Lincoln, a scientist at Fermilab, explains the hottest question in subatomic science—in terms most of us can understand!
What is antimatter?: Another good simple explanation from Don Lincoln.
How J.J. Thomson discovered the electron: This is a great little video that explains how scientists such as Thomson came to the conclusion that electrons must be charged particles inside atoms.
Please do NOT copy our articles onto blogs and other websites
Articles from this website are registered at the US Copyright Office. Copying or otherwise using registered works without permission, removing this or other copyright notices, and/or infringing related rights could make you liable to severe civil or criminal penalties.
Text copyright © Chris Woodford 2007, 2021. All rights reserved. Full copyright notice and terms of use.
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atoms是什么意思_atoms的翻译_音标_读音_用法_例句_爱词霸在线词典
s是什么意思_atoms的翻译_音标_读音_用法_例句_爱词霸在线词典首页翻译背单词写作校对词霸下载用户反馈专栏平台登录atoms是什么意思_atoms用英语怎么说_atoms的翻译_atoms翻译成_atoms的中文意思_atoms怎么读,atoms的读音,atoms的用法,atoms的例句翻译人工翻译试试人工翻译翻译全文简明柯林斯牛津atoms高中英 ['ætəm]美 ['ætəm]释义n.原子( atom的名词复数 ); 原子能; 微粒; 微量点击 人工翻译，了解更多 人工释义实用场景例句全部In graphite sheets, carbon atoms bond together in rings.石墨层中的碳原子相互连接形成碳环。柯林斯例句Atoms within the fluid interact with the minerals that form the grains.液体中的原子与形成颗粒的矿物质相互作用。柯林斯例句A nuclear reactor is the apparatus in which atoms are split.核反应堆是分裂原子的装置.《简明英汉词典》Water is made up of atoms of hydrogen and oxygen.水由氢和氧的原子构成.《简明英汉词典》Now with this particular piece of instrumentation, you can actually spot individual carbon atoms.现在利用这件特定的仪器，就可以真正观察到单个碳原子了。柯林斯例句pH is a measure of the concentration of free hydrogen atoms in a solution.pH值是测试溶液中自由氢原子浓度的单位。柯林斯例句All substances, whether they are gaseous, liquid or solid, are made of atoms.一切物质, 不论它们是气体 、 液体还是固体, 都是由原子构成的.《现代汉英综合大词典》Atoms of iron in the nail combine with atoms of oxygen from the air to form molecules of iron oxide, or rust.钉子里的铁原子与空气中的氧原子结合后形成氧化铁分子，也就是锈。柯林斯例句The carbon 14 atoms oxidise to carbon dioxide which gets blown about and mixed up with lower atmosphere.碳14原子氧化生成二氧化碳,向四周散去并与低空的大气混合.《简明英汉词典》Only 7 uranium atoms of every 1,000 are U - 235.在每1000个铀原子当中,只有七个是铀235.英汉非文学 - 科技The atoms of the various elements have different numbers of electrons.各种不同元素的原子中包含有不同数目的电子.英汉非文学 - 科技The carbon14 atoms oxidize to carbon dioxide which gets blown about and mixed up with lower atmosphere.碳14原子氧化生成二氧化碳，向四周散去并与低空的大气混合。辞典例句Polymers consist of long molecular chains of covalently bonded atoms.高聚物都是由共价链联接原子而形成的长链分子所组成.辞典例句The particles may be aggregates of atoms, molecules, or mixed materials.这些微粒可以由原子, 分子或混合物质聚集而成.辞典例句A chemical group is a submolecular group of atoms.化学基因是亚分子的原子集团.辞典例句收起实用场景例句真题例句全部六级高考Most hydrogen and oxygen atoms in water are stable, but traces of both elements are also present as heavier isotopes.2015年12月六级真题（第二套）听力 Section COn september 11, 1933, famous physicist Ernest Rutherford stated, with confidence, "anyone who expects a source of power in the transformation of these atoms is talking moonshine."2017年高考英语北京卷 阅读理解 阅读D 原文收起真题例句释义实用场景例句真Atoms & Molecules - Atom Definition, History, Structure of Atom & Molecules with Videos & Examples of Atoms and Molecules
Atoms & Molecules - Atom Definition, History, Structure of Atom & Molecules with Videos & Examples of Atoms and Molecules
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ChemistryAtoms and Molecules
Atoms and Molecules
What is an Atom? (Atom Definition)
Atoms are defined as “the basic building blocks of matter”.
Atom is the basic of all matter. They are very small and consist of even tinier particles. Neutrons, Protons, and Electrons are the basic particles making up the atom. They join together with other atoms and create matter. It takes many atoms to create anything.
It is the smallest constituent unit of matter that possess the properties of the chemical element. Atoms don’t exist independently, instead, they form ions and molecules which further combine in large numbers to form matter that we see, feel and touch.
What is a Molecule? (Molecule Definition)
A group of two or more atoms is linked together by sharing electrons in a chemical bond.
A molecule is a collection of two or more atoms that are securely bound together by attractive forces or by chemical bonds. The term “atom” refers to the tiniest unit of matter that can be separated. The term “valency” refers to an element’s capacity for combination.
Table of Content
Atoms and Molecules Definition
Recommended Videos
Atom Definition Chemistry
What is the Size of an Atom?
Relative Sizes
What are Atoms made of?
What is Atomic Mass?
Salient features of Dalton’s Atomic Theory
What is a Molecule?
Examples of Molecules
Forces between Atoms and Molecules
Frequently Asked Questions – FAQs
Atoms and Molecules Definition
Atoms are much too small to be seen; hence experiments to find out their structure and behavior have to be conducted with large numbers of them. From the results of these experiments, we may attempt to construct a hypothetical model of an atom that behaves like the true atom.
Molecules consist of one or more atoms bound together by covalent (chemical) bonds. Atoms may be depicted by circle shapes, each of which has a nucleus at the center (containing protons and neutrons), surrounded by one or more concentric circles representing the ‘shells’ or ‘levels’ in which the electrons surrounding the nucleus of the atom are located and markings indicating the electron.at each level. A molecule is the smallest thing a substance can be divided into while remaining the same substance. It is made up of two or more atoms that are bound together by chemical bonding.
Atoms and Molecules
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Atom Definition Chemistry
The smallest particle of an element, which may or may not have an independent existence but always takes place in a chemical reaction is called an atom. An atom is defined as the smallest unit that retains the properties of an element. An atom is composed of sub-atomic particles and these cannot be made or destroyed. All atoms of the same element are identical and different elements have different types of atoms. Chemical reactions occur when atoms are rearranged.
Atoms consist of three fundamental types of particles, protons, electrons and neutrons. Neutrons and protons have approximately the same mass and in contrast to this the mass of an electron is negligible. A proton carries a positive charge, a neutron has no charge and an electron is negatively charged. An atom contains equal numbers of protons and electrons and therefore overall an atom has no charge. The nucleus of an atom contains protons and neutrons only, and therefore is positively charged. The electrons occupy the region of space around the nucleus. Therefore, most of the mass is concentrated within the nucleus.
The center of the atom is called the nucleus. The nucleus contains neutrons and protons that give an atom its weight and positive charges. A neutron carries no charge and has a mass of one unit. A proton carries a single positive charge and also has a mass of one unit, The atomic number of an element is equal to the number of protons or positive charges in the nucleus. The atomic weight of an element is determined by combining the total number of protons and neutrons in the nucleus. An electron carries a single negative charge. If an atom of an element is to have zero charge, it must have the same number of electrons as protons. These electrons are arranged in orbits around the nucleus of the atom like the layers of an anion.
What is the Size of an Atom?
The size of an atom is extremely small, much smaller than our imagination. A layer of an atom as thick as a thin sheet of paper is formed when more than millions of atoms are stacked together. It is impossible to measure the size of an isolated atom because it’s difficult to locate the positions of electrons surrounding the nucleus.
However, the size of an atom can be estimated by assuming that the distance between adjacent atoms is equal to half the radius of an atom. Atomic radius is generally measured in nanometres.
\(\begin{array}{l}1 m = 10^{9}nm\end{array} \)
Relative Sizes
Examples
Radii (m)
Atom of Hydrogen
\(\begin{array}{l}10^{-10}m\end{array} \)
Molecule of water
\(\begin{array}{l}10^{-9}m\end{array} \)
Molecule of hemoglobin
\(\begin{array}{l}10^{-8}m\end{array} \)
Grain of Sand
\(\begin{array}{l}10^{-4}m\end{array} \)
What are Atoms made of?
An atom is composed of three particles, namely, neutrons, protons and electrons with hydrogen as an exception without neutrons.
Every atom has a nucleus that bounds one or more electrons around it.
The nucleus has typically a similar number of protons and neutrons which are together known as nucleons.
The protons are positively charged, electrons are negatively charged and neutrons are neutral.
What is Atomic Mass?
It is the mass of an atom in a chemical element. It is roughly equivalent to the total neutrons and protons present in the atom. It is expressed in atomic mass units (denoted by u). 1amu is equal to the exactly one-twelfth of the mass of 1 atom of C-12 and the relative atomic masses of elements is determined with respect to-12 atom.
Atomic masses of Some Elements
Elements
Atomic Mass (u)
Hydrogen
1
Carbon
12
Nitrogen
14
Oxygen
16
Sodium
23
Magnesium
24
Sulfur
32
Chlorine
35.5
Calcium
40
Salient features of Dalton’s Atomic Theory
The matter is composed of minute particles known as atoms.
Atoms are indivisible particles that can’t be destroyed or created through chemical reactions.
All atoms of an element have identical chemical properties and mass whereas, atoms of different elements have different chemical properties and masses.
Atoms combine in a ratio of small whole numbers to form compounds.
The matter is anything and everything in our surrounding. It has basic structural and fundamental units. Let us examine the concept of matter with an example. Taking a storybook into consideration and dividing its structure. The book contains many pages, each page consists of paragraphs, and each paragraph has many sentences.
Each sentence will further have many words and each word will have characters. Therefore we have divided a storybook into characters. This is exactly the same case when we take the matter into account. The matter is made up of substances which contain molecules. The molecules, in turn, are made up of groups of atoms.
Atoms in simple terms are defined as the smallest unit of matter. In ancient times scientists wondered whether the matter could be further divided or not. Around 500 BC the idea of divisibility of matter evolved in India. A scientist named Maharishi Kanad stated that matter can be divided into smaller and smaller units. The smallest unit of matter after which further division was not possible was known as parmanu.
What is a Molecule?
Molecule Definition
A molecule is defined as the smallest unit of a compound that contains the chemical properties of the compound.
Molecules are made up of groups of atoms. Describing the structure of an atom, an atom is also sub-divided into smaller units. Protons, electrons, and neutrons are sub-particles of an atom. The protons and neutrons are contained inside the nucleus of the atom and electrons revolve around the nucleus.
Protons are positively charged particles whereas electrons are negatively charged particles. Neutrons do not carry any charge. So we can say that the nucleus is positively charged due to the presence of protons. The nucleus is a bulk mass at the centre of an atom. Atoms are largely vacant.
Every element has a certain atomic number. The atomic number of an element is defined as the number of protons present in its nucleus. It is denoted by Z.
When we talk about the mass of atoms, the mass of their particles is taken into consideration. Electrons have negligible mass. Hence the mass of an atom is the sum of the mass of protons and neutrons. The mass number is denoted by A.
A molecule is the smallest unit (particle) of a compound having the physical and chemical properties of that compound. This does not mean that molecules can not be broken down into smaller parts, e.g. the atoms from which they are formed or the fragments of the molecule, each consisting of several atoms or parts of atoms.
A molecule is defined as the smallest unit of a compound that contains the chemical properties of the compound. Molecules are made up of groups of atoms. Describing the structure of an atom, an atom is also sub-divided into smaller units. Proton, electrons, and neutrons are sub-particles of an atom. The protons and neutrons are contained inside the nucleus of the atom and electrons revolve around the nucleus.
Examples of Molecules
A molecule is a collection of two or more atoms that make up the smallest recognisable unit into which a pure material may be split while maintaining its makeup and chemical characteristics. Some examples of molecules are
H2O (water)
N2 (nitrogen)
O3 (ozone)
CaO (calcium oxide)
C6H12O6 (glucose, a type of sugar)
NaCl (table salt)
Forces between Atoms and Molecules
The simplest forces between atoms are those which arise as a result of electron transfer. A simple example is that of say sodium fluoride. The sodium atom has a nuclear charge of +11, with 2 electrons in the K shell, 8 in the L shell and 1 in the M shell. The fluorine atom has a nuclear charge of 9 with 2 electrons in the K shell and 7 in the L shell.
The outermost electron in the sodium atom may transfer readily to the fluorine atom; both atoms then have a complete shell but the sodium now has a net charge of +1 and the fluorine a net charge of -1. These ions, therefore, attract one another by direct coulombic interaction. The force between them is strong it varies as x-2, where x is the distance between the ions, and it acts in the direction of the line joining the ions.
Frequently Asked Questions – FAQsQ1 How do atoms become molecules?
As atoms come together to form molecules, chemical bonds bind them together. As a consequence of sharing or exchanging electrons between the atoms, these bonds form. It is only the electrons that are ever active in bonding in the outermost shell.
Q2 What is a simple molecule?
Water is known to be a basic molecule consisting of a few atoms. Basic molecular substances are molecules in which strong covalent bonds bind the atoms. Nevertheless, weak forces bind the molecules together so that they have high melting and boiling points.
Q3 Is ozone a molecule?
Ozone is a molecule made up of three atoms of oxygen. The chemical ozone symbol is O3 as the oxygen atom symbol is O. Most of the ozone present in our atmosphere is produced by a sun-emitted association of oxygen molecules with ultraviolet radiation.
Q4 Can a molecule have one atom?
An electrically neutral group of two or more atoms held together by chemical bonds is the most basic definition of molecule. In that sense, no, by nature, a molecule can not be formed from a single atom.
Q5 What is the structure of an atom?
Atoms are composed of three elementary particles: protons, electrons , and neutrons. The atom’s nucleus (center) contains the protons (positively charged) and neutrons (without charge). The atom’s outermost regions are called electron shells, which contain (negative charged) electrons.
Q6 Is Salt a molecule?
Molecules are subject to molecular bonds. Something like table salt ( NaCl) is a compound because it is made of more than one type of element (sodium and chlorine), but it is not a molecule because it is an ionic bond that holds NaCl together. We can say sodium chloride is an ionic compound.
Q7 What is Atom and example?
Many atoms consist of a positively charged nucleus consisting of protons and neutrons surrounded by a cloud of electrons charged negatively. An atom is any particle of matter at its most basic level which contains at least one proton. Here are some examples of the atoms: hydrogen (H) and neon (Ne).
Q8 What is the work of an atom?
The protons and neutrons are packed together into the center of the atom (which is called the nucleus) and the much smaller electrons, whizzing around the outside. When people draw images of atoms they show the electrons like satellites spinning in orbits around the Earth.
Q9 What is the difference between atoms and molecules?
A tiny particle of a chemical element is called an atom, which may or may not exist independently. Molecules refer to the group of atoms that the bond binds together, representing the smallest unit in a compound. Two or more identical or distinct atoms are chemically bonded.
Q10 Is oxygen a molecule?Oxygen is a molecule made up of two atoms of oxygen bound by a covalent double bond to form dioxygen or O2
We have briefly seen the properties of atoms and molecules. Stay tuned with BYJU’S for more information on Atoms and Molecules.
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Post My Comment
Aman Yadav
July 15, 2020 at 7:35 pm
It’s really very good way for study
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Adnan
August 11, 2020 at 8:02 pm
Sir please explain me sublimation process
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Mentor
August 12, 2020 at 10:20 am
Sublimation is the conversion between the solid and the gaseous phases of matter, with no intermediate liquid stage. For those of us interested in the water cycle, sublimation is most often used to describe the process of snow and ice changing into water vapour in the air without first melting into water.
Click here to learn more about Sublimation.
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TGMAIL
January 3, 2021 at 3:11 pm
What is the structure of an atom?
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Mentor
January 4, 2021 at 9:59 am
Three fundamental particles are composed of atoms: protons, electrons, and neutrons. Protons (positively charged) and neutrons are in the nucleus (centre) of the atom (no charge). Electron shells are considered the outermost regions of the atom which contain electrons (negatively charged).
Reply
RITHICK
February 28, 2021 at 9:12 pm
Sir, what are elements?
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Mentor
March 1, 2021 at 10:10 am
An element is a substance that cannot be broken down into any other substance. In chemistry, an element is a pure substance consisting only of atoms that all have the same numbers of protons in their atomic nuclei.
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a rai
March 2, 2021 at 6:25 pm
why do they take c12 to find mass of other atoms in earlier days
Reply
Mentor
March 3, 2021 at 10:21 am
Atomic mass is based on a relative scale and the mass of 12C (carbon twelve) is defined as 12amu; so, this is an exact number. Each carbon atom has the same number of protons and electrons, 6. 12C has 6 neutrons, 13C has 7 neutrons, and 14C has 8 neutrons and so on. So, we must specify which C atom defines the scale.
Reply
banuja
July 24, 2021 at 11:43 pm
how C6H12O6 is a molecule?. it consists of different elements. then, how it is a molecule
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Mentor
July 26, 2021 at 10:20 am
Sugar is a glucose molecule which consists of 6 carbon atoms bonded together as a chain with additional atoms of oxygen and hydrogen.
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Kaushik singh
September 2, 2021 at 12:14 am
how H20 is a molecule but NaCl is a compound??
Reply
Mentor
September 2, 2021 at 11:13 am
Because it has molecular bonds, water is a molecule. Water is a compound because it is made up of several different elements (oxygen and hydrogen). Water can be considered a molecular substance.
Table salt (NaCl) is a compound since it contains two different elements (sodium and chlorine), but it is not a molecule because the bond that binds it together is an ionic bond. It’s possible to classify sodium chloride as an ionic substance.
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Sayeedur Rahman
December 13, 2021 at 7:07 pm
Sir, what is an Atom?
Please reply???
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Mentor
December 14, 2021 at 11:10 am
Atom, smallest unit into which matter can be divided without the release of electrically charged particles. It also is the smallest unit of matter that has the characteristic properties of a chemical element. As such, the atom is the basic building block of chemistry. Click here to learn more about Atoms.
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Kishor
November 4, 2022 at 7:14 am
What is sub shell? Sir
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Mentor
November 4, 2022 at 4:41 pm
A subshell is a subdivision of electron shells separated by electron orbitals. Subshells are labelled s, p, d, and f in an electron configuration.
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Kishor
November 4, 2022 at 7:16 am
What is valency
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Mentor
November 4, 2022 at 4:42 pm
Valency is the combining power of an element. Elements in the same group of the periodic table have the same valency. The valency of an element is related to how many electrons are in the outer shell.
Read more: Valency
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Atomic Model (Atomic Theory) - Definition, Theory, Structure, number, Mass and Atomic species with examples and FAQs
Atomic Model (Atomic Theory) - Definition, Theory, Structure, number, Mass and Atomic species with examples and FAQs
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ChemistryAtoms and MoleculesAtomic
Atomic Model (Atomic Chemistry)
What is Atomic Chemistry?
An atom is the smallest unit of ordinary matter that forms a chemical element.
Atoms are made of fundamental particles called protons, neutrons, and electrons. Protons and neutrons clump together to form a central nucleus. The electrons move in a cloud-like region around the nucleus. Most atoms are stable. Their protons, neutrons, and electrons balance.
The electrons of an atom are attracted to the protons in an atomic nucleus by the electromagnetic force. The protons and neutrons in the nucleus are attracted to each other by the nuclear force.
Some atoms have too many neutrons in the nucleus, which makes them unstable. They’re radioactive, giving off particles until they become stable. Atoms with extra or missing electrons are called ions. They have a positive or negative electric charge and are responsible for many chemical reactions.
Table of Contents
Atomic Theory
Atomic Structure
Atomic symbol
Atomic number
Atomic mass
Different atomic species
FAQs
Atomic Theory
Dalton’s Atomic Theory
According to the postulates proposed by Dalton, the atomic structure comprised atoms, the smallest particle responsible for the chemical reactions to occur.
Postulates of Dalton’s Atomic Theory
The following are the postulates of his theory:
Every matter is made up of atoms.
Atoms are indivisible.
Specific elements have only one type of atom in them.
Each atom has its own constant mass that varies from element to element..
Atoms can neither be created nor be destroyed but can be transformed from one form to another.
Dalton’s atomic theory successfully explained the Laws of chemical reactions, namely, the Law of conservation of mass, Law of constant properties, Law of multiple proportions, and Law of reciprocal proportions.
Discovery of subatomic particles electrons, protons, and neutrons discarded the indivisible nature of the atom proposed by John Dalton.
Atomic Structure
From the several experiments scientists proved that an atom was not the smallest indivisible particle but had a complex structure of its own and is made up of smaller particles like electrons, protons, and neutrons, etc. These particles are termed as subatomic particles.
Subatomic particle
Charge of subatomic particle
Discovered
Electron
Negative (e)
J.J Thomson
Proton
Positive (p)
Ernest Rutherford
Neutron
No charge (n)
James Chadwick
To explain the distribution of various subatomic particles inside the atom several models were proposed. These were called atomic models.
Thomson Model of Atom
It was proposed by JJ Thomson, in 1898. According to this model, an atom possesses a spherical shape in which the positive charge is uniformly distributed.
This model can be visualized as a pudding with plums or watermelon of positive charge with seeds (electrons) embedded into it. Hence, it is also called plum pudding, raisin pudding, or watermelon model.
Limitations of Thomson Model
Although this model was able to explain the overall neutrality of the atom, it was not consistent with the results of later experiments, like the α-ray scattering experiment.
Rutherford Model of Atom
The positively charged particles and most of the mass of an atom were concentrated in an extremely small volume called the nucleus. Nucleus is made up of nucleons.( neutrons + protons)
There is an empty space around the nucleus called the extranuclear part, in this part electrons are present. Electrons revolve around the nucleus in closed orbits with high speed. The centrifugal force acting on the revolving electrons is being counterbalanced by the force of attraction between the electrons and the nucleus.
Limitations of Rutherford Model
According to classical electromagnetic theory, accelerated charged particles emit electromagnetic radiation and hence an electron revolving around the nucleus should emit electromagnetic radiation. This radiation would carry energy from the motion of the electron which would come at the cost of shrinking of orbits. Ultimately the electrons would collapse in the nucleus. So Rutherford model was not in accordance with classical electromagnetic and could not explain the stability of an atom.
Bohr’s Model of Atom
Postulates of Bohr’s model are:
Electrons revolve around the nucleus in a specific circular path known as orbital, energy of each orbital is constant.
Energy absorbed or emitted during the transition is given by ΔE = hν
The angular momentum of an electron present in any orbital must be an integral multiple of h/2π
Limitations of Bohr’s Model
Bohr’s model was not able to explain the Heisenberg uncertainty principle.
It failed to explain the Stark effect (effect of electric field on the spectra of atoms).
It is also failed to explain the Zeeman Effect (effect of magnetic field on the spectra of atoms)
Recommended Video
Atomic Models – Structure of Atom
Atomic Symbol
Atom of an element is represented in the form of an atomic symbol.
Element
Atomic symbol
Hydrogen
H
Helium
He
Lithium
Li
Beryllium
Be
Boron
B
To know the atomic symbol of 118 element you may visit ➡ Atomic symbol
Atomic Number (z)
The number of protons present in the nucleus of an atom is equal to its atomic number (Z).
Thus Atomic number (Z) = number of protons in the nucleus of an atom
Example Atomic number of Carbon(C) = 6 = number of protons
To know the atomic number of 118 elements you may visit ➡ Atomic number
Atomic Mass (A)
Atomic mass is equal to the sum of protons and neutrons present in the nucleus of the atom.
Thus Atomic mass = number of protons + number of neutrons
For Example Atomic mass of carbon = 12
To know the atomic mass of element you may visit ➡ Atomic mass
Different Atomic Species
The types of atomic species are:
Isotopes
Atoms of the same element which have the same atomic number (or number of protons) but have different mass numbers (or number of neutrons) are called isotopes.
To learn more about its properties you may visit Isotopes of elements
Isobars
Atoms of different elements that have the same mass number but different atomic numbers are called Isobars.
To learn more about the difference between isotopes and isobars visit Isotopes and isobar
Frequently Asked Questions on AtomicQ1 Who discovered atoms?
The idea that everything is made of atoms was pioneered by John Dalton.
Q2 What is an atom made of?
Atoms are made of fundamental particles called protons, neutrons, and electrons. Protons and neutrons clump together to form a central nucleus. The electrons move in a cloud-like region around the nucleus.
Q3 Are atoms particles or waves?
All matter, which appears to be particulate, can also behave like waves. Atoms are both particles or waves.
Q4 Can an element be one atom?
The simplest structural unit of an element is an atom. An element is a substance that is made entirely from one type of atom.
Q5 What are atomic mass and atomic number?
Atomic mass is equal to the sum of protons and neutrons present in the nucleus of the atom. The number of protons present in the nucleus of an atom is equal to its atomic number.
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Important Chemistry Topics
Periodic Table of Elements
Aufbau Principle
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2.2: Atomic Structure - Chemistry LibreTexts
2.2: Atomic Structure - Chemistry LibreTexts
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CHE 183: Principles of Chemistry I
2: Atoms and Molecules
2.2: Atomic Structure
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2.2: Atomic Structure
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A Short History of the Atomic StructureKey TakeawaysCitations and attributions
Learning Objectives
State the modern atomic theory.
Learn how atoms are constructed.
The smallest piece of an element that maintains the identity of that element is called an atom. Individual atoms are extremely small. It would take about fifty million atoms in a row to make a line that is 1 cm long. The period at the end of a printed sentence has several million atoms in it. Atoms are so small that it is difficult to believe that all matter is made from atoms—but it is.
The concept that atoms play a fundamental role in chemistry is formalized by the modern atomic theory, first stated by John Dalton, an English scientist, in 1808. It consists of three parts:
All matter is composed of atoms.
Atoms of the same element are the same; atoms of different elements are different.
Atoms combine in whole-number ratios to form compounds.
These concepts form the basis of chemistry. Although the word atom comes from a Greek word that means "indivisible," we understand now that atoms themselves are composed of smaller parts called subatomic particles. The first part to be discovered was the electron, a tiny subatomic particle with a negative charge. It is often represented as e−, with the right superscript showing the negative charge. Later, two larger particles were discovered. The proton is a more massive (but still tiny) subatomic particle with a positive charge, represented as p+. The neutron is a subatomic particle with about the same mass as a proton, but no charge. It is represented as either n or n0. We now know that all atoms of all elements are composed of electrons, protons, and (with one exception) neutrons. Table \(\PageIndex{1}\) summarizes the properties of these three subatomic particles.
Table \(\PageIndex{1}\): Properties of the Three Subatomic Particles
Name
Symbol
Mass (approx.; kg)
Charge
Proton
p+
1.6 × 10−27
1+
Neutron
n, n0
1.6 × 10−27
none
Electron
e−
9.1 × 10−31
1−
How are these particles arranged in atoms? They are not arranged at random. Experiments by Ernest Rutherford in England in the 1910s pointed to a nuclear model with atoms that has the protons and neutrons in a central nucleus with the electrons in orbit about the nucleus. The relatively massive protons and neutrons are collected in the center of an atom, in a region called the nucleus of the atom (plural nuclei). The electrons are outside the nucleus and spend their time orbiting in space about the nucleus. (Figure \(\PageIndex{1}\)).
Figure \(\PageIndex{1}\): The Structure of the Atom. Atoms have protons and neutrons in the center, making the nucleus, while the electrons orbit the nucleus.
The modern atomic theory states that atoms of one element are the same, while atoms of different elements are different. What makes atoms of different elements different? The fundamental characteristic that all atoms of the same element share is the number of protons. All atoms of hydrogen have one and only one proton in the nucleus; all atoms of iron have 26 protons in the nucleus. This number of protons is so important to the identity of an atom that it is called the atomic number. The number of protons in an atom is the atomic number of the element. Thus, hydrogen has an atomic number of 1, while iron has an atomic number of 26. Each element has its own characteristic atomic number.
Atoms of the same element can have different numbers of neutrons, however. Atoms of the same element (i.e., atoms with the same number of protons) with different numbers of neutrons are called isotopes. Most naturally occurring elements exist as isotopes. For example, most hydrogen atoms have a single proton in their nucleus. However, a small number (about one in a million) of hydrogen atoms have a proton and a neutron in their nuclei. This particular isotope of hydrogen is called deuterium. A very rare form of hydrogen has one proton and two neutrons in the nucleus; this isotope of hydrogen is called tritium. The sum of the number of protons and neutrons in the nucleus is called the mass number of the isotope.
Neutral atoms have the same number of electrons as they have protons, so their overall charge is zero. However, as we shall see later, this will not always be the case.
Example \(\PageIndex{1}\):
The most common carbon atoms have six protons and six neutrons in their nuclei. What are the atomic number and the mass number of these carbon atoms?
An isotope of uranium has an atomic number of 92 and a mass number of 235. What are the number of protons and neutrons in the nucleus of this atom?
Solution
If a carbon atom has six protons in its nucleus, its atomic number is 6. If it also has six neutrons in the nucleus, then the mass number is 6 + 6, or 12.
If the atomic number of uranium is 92, then that is the number of protons in the nucleus. Because the mass number is 235, then the number of neutrons in the nucleus is 235 − 92, or 143.
Exercise \(\PageIndex{1}\)
The number of protons in the nucleus of a tin atom is 50, while the number of neutrons in the nucleus is 68. What are the atomic number and the mass number of this isotope?
Answer
Atomic number = 50, mass number = 118
When referring to an atom, we simply use the element's name: the term sodium refers to the element as well as an atom of sodium. But it can be unwieldy to use the name of elements all the time. Instead, chemistry defines a symbol for each element. The atomic symbol is a one- or two-letter representation of the name of an element. By convention, the first letter of an element's symbol is always capitalized, while the second letter (if present) is lowercase. Thus, the symbol for hydrogen is H, the symbol for sodium is Na, and the symbol for nickel is Ni. Most symbols come from the English name of the element, although some symbols come from an element's Latin name. (The symbol for sodium, Na, comes from its Latin name, natrium.) Table \(\PageIndex{2}\) lists some common elements and their symbols. You should memorize the symbols in Table \(\PageIndex{2}\), as this is how we will be representing elements throughout chemistry.
Table \(\PageIndex{2}\): Names and Symbols of Common Elements
Element Name
Symbol
Element Name
Symbol
Aluminum
Al
Mercury
Hg
Argon
Ar
Molybdenum
Mo
Arsenic
As
Neon
Ne
Barium
Ba
Nickel
Ni
Beryllium
Be
Nitrogen
N
Bismuth
Bi
Oxygen
O
Boron
B
Palladium
Pd
Bromine
Br
Phosphorus
P
Calcium
Ca
Platinum
Pt
Carbon
C
Potassium
K
Chlorine
Cl
Radium
Ra
Chromium
Cr
Radon
Rn
Cobalt
Co
Rubidium
Rb
Copper
Cu
Scandium
Sc
Fluorine
F
Selenium
Se
Gallium
Ga
Silicon
Si
Germanium
Ge
Silver
Ag
Gold
Au
Sodium
Na
Helium
He
Strontium
Sr
Hydrogen
H
Sulfur
S
Iodine
I
Tantalum
Ta
Iridium
Ir
Tin
Sn
Iron
Fe
Titanium
Ti
Krypton
Kr
Tungsten
W
Lead
Pb
Uranium
U
Lithium
Li
Xenon
Xe
Magnesium
Mg
Zinc
Zn
Manganese
Mn
Zirconium
Zr
The elements are grouped together in a special chart called the periodic table of all the elements. A simple periodic table is shown in Figure \(\PageIndex{2}\), while one may view a more extensive periodic table from another source. The elements on the periodic table are listed in order of ascending atomic number. The periodic table has a special shape that will become important to us when we consider the organization of electrons in atoms (Chapter 8). One immediate use of the periodic table helps us identify metals and nonmetals. Nonmetals are in the upper right-hand corner of the periodic table, on one side of the heavy line splitting the right-side part of the chart. All other elements are metals.
Figure \(\PageIndex{1}\): A Simple Periodic Table
There is an easy way to represent isotopes using the atomic symbols. We use the construction:
\[\ce{_{Z}^{A}X}\nonumber \]
where \(X\) is the symbol of the element, \(A\) is the mass number, and \(Z\) is the atomic number. Thus, for the isotope of carbon that has 6 protons and 6 neutrons, the symbol is:
\[\ce{_{6}^{12}C}\nonumber \]
where \(C\) is the symbol for the element, 6 represents the atomic number, and 12 represents the mass number.
Example \(\PageIndex{2}\):
What is the symbol for an isotope of uranium that has an atomic number of 92 and a mass number of 235?
How many protons and neutrons are in \(\ce{_{26}^{56}Fe}\)
Solution
The symbol for this isotope is \(\ce{_{92}^{235}U}\)
This iron atom has 26 protons and 56 − 26 = 30 neutrons.
Exercise \(\PageIndex{2}\)
How many protons are in \(\ce{_{11}^{23} Na}\)
Answer
11 protons
It is also common to state the mass number after the name of an element to indicate a particular isotope. Carbon-12 represents an isotope of carbon with 6 protons and 6 neutrons, while uranium-238 is an isotope of uranium that has 146 neutrons.
A Short History of the Atomic Structure
The basic idea that matter is made up of tiny indivisible particles is very old, appearing in many ancient cultures such as Greece and India. The word atom is derived from the ancient Greek word atomos, which means "indivisible". This ancient idea was based on philosophical reasoning rather than scientific reasoning, and modern atomic theory was developed throughout a few centuries of research and experimentation.
The first atomic theory based on experimentation was stated by John Dalton, an English scientist, in 1808. By studying the chemical composition of different oxides, Dalton noticed that elements combined in very specific patterns given by small whole numbers. This observation prompted him to support that all matter is made of atoms, although Dalton had no idea about the actual structure of the atoms.
In 1897, J. J. Thomson discovered that the existence of the first subatomic particle. He renamed these new negatively charged particles as electrons. To explain the overall neutral charge of the atom, Thomson concluded that these electrons must be embedded in an uniform sea of positive charge. In this "plum pudding atomic model", the electrons were seen as embedded in the positive charge like raisins in a plum pudding.
Between 1908 and 1913, Ernest Rutherford and his colleagues Hans Geiger and Ernest Marsden came to have doubts about the Thomson model. Rutheford performed a series of experiments in which they bombarded thin foils of metal with positively charged alpha particles. They spotted alpha particles being deflected by angles greater than 90°. To explain this, Rutherford proposed that the positive charge of the atom is not distributed throughout the atom's volume as Thomson believed, but is concentrated in a tiny nucleus at the center. Rutherford's atomic model introduced the existence of the positively charged nucleus surrounded by the negatively charged electrons.
In 1913, after studying atomic spectra produced by elements. the physicist Niels Bohr proposed a model in which the electrons of an atom were assumed to orbit the nucleus but could only do so in a finite set of orbits, and could jump between these orbits only in discrete changes of energy corresponding to absorption or radiation of a photon. This quantized atomic model, also known as the planetary model of the atom, was used to explain why the electrons' orbits are stable and why elements absorb and emit electromagnetic radiation in discrete lines. The Bohr model of the atom was the first complete physical model of the atom. It described the overall structure of the atom and how atoms bond to each other. Bohr's planetary atomi model was not perfect and was soon superseded by the more accurate Schrödinger model, but it is sufficient to understand most chemical and physical properties discussed in this course.
In 1924, Louis de Broglie had proposed that all particles behave like waves to some extent, including the electron. In 1926 Erwin Schrödinger used this idea to develop the Schrödinger model of the atom. In this model, electrons are considered electromagnetic waves mechanics rather than particles. According to this model, it is mathematically impossible to obtain precise values for both the position and the energy (momentum) of an electron at a given point in time. This idea became the uncertainty principle, formulated by Werner Heisenberg in 1927. Because it is impossible to determine the position and the energy of an electron in an atom, Schrödinger's atomic model is based on the "probability" of finding an electron in a certain region around the nucleus. Thus, the orbits in the planetary model of the atom were discarded in favor of atomic orbitals, which are zones around the nucleus where a given electron is most likely to be observed.
Figure \(\PageIndex{2}\):A summary of atomic models. Image by Compound Interest (2016) https://www.compoundchem.com/2016/10/13/atomicmodels/. Shared under CC BY-NC-ND 4.0 license
Key Takeaways
Chemistry is based on the modern atomic theory, which states that all matter is composed of atoms.
Atoms themselves are composed of protons, neutrons, and electrons.
Each element has its own atomic number, which is equal to the number of protons in its nucleus.
Isotopes of an element contain different numbers of neutrons.
Elements are represented by an atomic symbol.
The periodic table is a chart that organizes all the elements.
Citations and attributions
" Atomic Theory" by LibreTexts is licensed under CC BY-NC-SA .
Wikipedia contributors. (2021, May 6). Atom. In Wikipedia, The Free Encyclopedia. Retrieved 15:20, May 18, 2021, from https://en.wikipedia.org/w/index.php?title=Atom&oldid=1021695004
Wikipedia contributors. (2021, May 8). J. J. Thomson. In Wikipedia, The Free Encyclopedia. Retrieved 15:21, May 18, 2021, from https://en.wikipedia.org/w/index.php?title=J._J._Thomson&oldid=1022092604
2.2: Atomic Structure is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by LibreTexts.
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