The Nucleus: The Center of an Atom - dummies The Nucleus: The Center of an Atom The Nucleus: The Center of an Atom The Nucleus: The Center of an Atom The nucleus, that dense central core of the atom, contains both protons and neutrons. Electrons are outside the nucleus in energy levels. Protons have a positive charge, neutrons have no charge, and electrons have a negative charge. A neutral atom contains equal numbers of protons and electrons. But the number of neutrons within an atom of a particular element can vary. Atoms of the same element that have differing numbers of neutrons are called isotopes. The following diagram shows the symbolization chemists use to represent a specific isotope of an element. In this diagram: X represents the chemical symbol of the element found on the periodic table. Z represents the atomic number. A represents the mass number (also called the atomic weight). Suppose you want to represent uranium. You can refer to a periodic table or a list of elements, and find that the symbol for uranium is U, its atomic number is 92, and its mass number is 238.

So, you can represent uranium as shown here: You know that uranium has an atomic number of 92 (number of protons) and mass number of 238 (protons plus neutrons). So if you want to know the number of neutrons in uranium, all you have to do is subtract the atomic number (92 protons) from the mass number (238 protons plus neutrons). The resulting number shows that uranium has 146 neutrons. But how many electrons does uranium have? Because the atom is neutral (it has no electrical charge), there must be equal numbers of positive and negative charges inside it, or equal numbers of protons and electrons. So there are 92 electrons in each uranium atom. The nucleus is very, very small and very, very dense when compared to the rest of the atom. Not only is the nucleus very small, but it also contains most of the mass of the atom. In fact, for all practical purposes, the mass of the atom is the sum of the masses of the protons and neutrons. The protons of an atom are all crammed together inside the nucleus. Each proton carries a positive charge, and like charges repel each other.

However, forces in the nucleus counteract this repulsion and hold the nucleus together. (Physicists call these forces nuclear glue. But sometimes this “glue” isn’t strong enough, and the nucleus does break apart. This process is called radioactivity.) What is the center of an atom called? | Reference.com What is the center of an atom called? A: Quick Answer The center of an atom is called the atom's nucleus. This structure is usually composed of protons and neutrons though some atoms of hydrogen have only protons. Full Answer The other main part of an atom is the electron cloud that hovers around the nucleus. Although the nucleus only takes up around a trillionth of an atom's space, it accounts for 99.9 percent of the atom's mass. The protons and neutrons in an atom's nucleus are held together by the residual strong force, which is also called the nuclear force. This force is more than 1000 times stronger than gravity, but it operates only within the nucleus of the atom.

High School Chemistry/Further Understanding of the Atom - Wikibooks, open books for an open world High School Chemistry/Further Understanding of the Atom From Wikibooks, open books for an open world 9 Vocabulary In the last lesson, you learned about the atom, and the early experiments that led to the development of Dalton's Atomic Theory. But Dalton's Atomic Theory isn't the end of the story. Do you remember the scientific method introduced in early on in the book? Chemists using the scientific method make careful observations and measurements and then use these measurements to propose theories. That’s exactly what Dalton did. Dalton used the following observations: Mass is neither created nor destroyed during a chemical reaction. Elements always combine in the same proportions by mass when they form a given compound. When elements form more than one compound, the different masses of one element that are combined with the same mass of the other element are in a ratio of small whole numbers. With these observations (which came from careful measurement), Dalton proposed his Atomic Theory – a model which suggested how the underlying structure of matter might lead to the three observations above. The scientific method, though, doesn't stop once a theory has been proposed.

Instead, the theory should suggest new experiments that can be performed to test whether or not the original theory is accurate and complete. Dalton's Atomic Theory held up well to a lot of the different chemical experiments that scientists performed to test it. In fact, for almost 100 years, it seemed as if Dalton's Atomic Theory was the whole truth. However, in 1897, a scientist named J. J. Thompson conducted some research which suggested that Atomic Theory wasn’t the entire story. As it turns out, Dalton had a lot right. He was right in saying matter is made up of atoms; he was right in saying there are different kinds of atoms with different mass and other properties; he was "almost" right in saying atoms of a given element are identical; he was right in saying during a chemical reaction, atoms are merely rearranged; he was right in saying a given compound always has atoms present in the same relative numbers. But he was wrong in saying atoms were indivisible or indestructible. As it turns out, atoms are divisible. In fact, atoms are composed of smaller subatomic particles. Explain the experiment that led to Thomson's discovery of the electron.

Describe Thomson's "plum pudding" model of the atom. Describe Rutherford's Gold Foil experiment, and explain how this experiment proved that the "plum pudding" model of the atom was incorrect. Thomson Discovered Electrons Were Part of the Atom[ edit ] In the mid-1800s, scientists were beginning to realize that the study of chemistry and the study of electricity were actually related. First, a man named Michael Faraday showed how passing electricity through mixtures of different chemicals could cause chemical reactions. Shortly after that, scientists found that by forcing electricity through a tube filled with gas, the electricity made the gas glow! Scientists didn't, however, understand the relationship between chemicals and electricity until a British physicist named J. J. Thomson (Figure 4.7) began experimenting with what is known as a cathode ray tube. Figure 4.7: A portrait of J. J. Thomson. The below figure shows a basic diagram of a cathode ray tube like the one J. J. Thomson would have used.

A cathode ray tube is a small glass tube with a cathode (a negatively charged metal plate) and an anode (a positively charged metal plate) at opposite ends. By separating the cathode and anode by a short distance, the cathode ray tube can generate what are known as "cathode rays" – rays of electricity that flowed from the cathode to the anode, J. J. Thomson wanted to know what cathode rays were, where cathode rays came from and whether cathode rays had any mass or charge. The techniques that J. J. Thomson used to answer these questions were very clever and earned him a Nobel Prize in physics. First, by cutting a small hole in the anode J. J. Thomson found that he could get some of the cathode rays to flow through the hole in the anode and into the other end of the glass cathode ray tube. Next, J. J. Thomson figured out that if he painted a substance known as "phosphor" onto the far end of the cathode ray tube, he could see exactly where the cathode rays hit because the cathode rays made the phosphor glow. A cathode ray tube. J.

J. Thomson must have suspected that cathode rays were charged, because his next step was to place a positively charged metal plate on one side of the cathode ray tube and a negatively charged metal plate on the other side of the cathode ray tube, as shown in the below figure. The metal plates didn't actually touch the cathode ray tube, but they were close enough that a remarkable thing happened! The flow of the cathode rays passing through the hole in the anode was bent upwards towards the positive metal plate and away from the negative metal plate. A cathode ray was attracted to the positively charged metal plate placed above the tube, and repelled from negatively charged metal plate placed below the tube. In other words, instead of the phosphor glowing directly across from the hole in the anode (as in the first figure), the phosphor now glowed at a spot quite a bit higher in the tube (as in the second figure). J. J. Thomson thought about his results for a long time. It was almost as if the cathode rays were attracted to the positively charged metal plate above the cathode ray tube, and repelled from the negatively charged metal plate below the cathode ray tube. J. J.

Thomson knew that charged objects are attracted to and repelled from other charged objects according to the rule: opposites attract, likes repel. This means that a positive charge is attracted to a negative charge, but repelled from another positive charge. Similarly, a negative charge is attracted to a positive charge, but repelled from another negative charge. Using the "opposites attract, likes repel" rule, J. J. Thomson argued that if the cathode rays were attracted to the positively charged metal plate and repelled from the negatively charged metal plate, they themselves must have a negative charge! J. J. Thomson then did some rather complex experiments with magnets, and used his results to prove that cathode rays were not only negatively charged, but also had mass. Remember that anything with mass is part of what we call matter. In other words, these cathode rays must be the result of negatively charged "matter" flowing from the cathode to the anode. But there was a problem. According to J. J. Thomson's measurements, either these cathode rays had a ridiculously high charge, or else had very, very little mass – much less mass than the smallest known atom. How was this possible?

How could the matter making up cathode rays be smaller than an atom if atoms were indivisible? J. J. Thomson made a radical proposal: maybe atoms are divisible. J. J. Thomson suggested that the small, negatively charged particles making up the cathode ray were actually pieces of atoms. He called these pieces "corpuscles", although today we know them as "electrons". Thanks to his clever experiments and careful reasoning J. J. Thomson is credited with the discovery of the electron. Protons Were Thought to Exist but Discovered Much Later[ edit ] In the last section, we learned that atoms are, in fact, divisible, and that one of the subatomic particles making up an atom is a small, negatively charged entity called an "electron". Now imagine what would happen if atoms were made entirely of electrons. First of all, electrons are very, very small; in fact, electrons are about 2000 times smaller than the smallest known atom, so every atom would have to contain a whole lot of electrons. But there's another, even bigger problem: electrons are negatively charged.

Therefore, if atoms were made entirely out of electrons, atoms would be negatively charged themselves… and that would mean all matter was negatively charged as well. Of course, matter isn't negatively charged. In fact, most matter is what we call neutral – it has no charge at all. If matter is composed of atoms, and atoms are composed of negative electrons, how can matter be neutral? The only possible explanation is that atoms consist of more than just electrons. Atoms must also contain some type of positively charged material which balances the negative charge on the electrons. Negative and positive charges of equal size cancel each other out, just like negative and positive numbers of equal size. What do you get if you add +1 and −1? You get 0, or nothing. That's true of numbers, and that's also true of charges. If an atom contains an electron with a −1 charge, but also some form of material with a +1 charge, overall the atom must have a (+1) + (−1) = 0 charge – in other words, the atom must be neutral, or have no charge at all. Based on the fact that atoms are neutral, and based on J. J.

Thomson's discovery that atoms contain negative subatomic particles called "electrons", scientists assumed that atoms must also contain a positive substance. It turned out that this positive substance was another kind of subatomic particle, known as the "proton". Although scientists knew that atoms had to contain positive material, protons weren't actually discovered, or understood, until quite a bit later. Thomson's Model of the Atom[ edit ] Figure 4.8: Thomson's "plum-pudding" model for the atom. Notice how the "plums" are the negatively charged electrons, while the positive charge is spread throughout the entire pudding batter. When Thomson discovered the negative electron, he realized that atoms had to contain positive material as well – otherwise they wouldn't be neutral overall. As a result, Thomson formulated what's known as the "plum pudding" model for the atom. According to the "plum pudding" model, the negative electrons were like pieces of fruit and the positive material was like the batter or the pudding. This made a lot of sense given Thomson's experiments and observations. Thomson had been able to isolate electrons using a cathode ray tube; however he had never managed to isolate positive particles.

As a result, Thomson theorized that the positive material in the atom must form something like the "batter" in a plum pudding, while the negative electrons must be scattered through this "batter". (If you've never seen or tasted a plum pudding, you can think of a chocolate chip cookie instead. In that case, the positive material in the atom would be the "batter" in the chocolate chip cookie, while the negative electrons would be scattered through the batter like chocolate chips.) Figure 4.8 shows a "plum pudding" and a "plum pudding" model for the atom. Notice how easy it would be to pick the pieces of fruit out of a plum pudding. On the other hand, it would be a lot harder to pick the batter out of the plum pudding, because the batter is everywhere. If an atom were similar to a plum pudding in which the electrons are scattered throughout the "batter" of positive material, then you'd expect it would be easy to pick out the electrons, but a lot harder to pick out the positive material. Everything about Thomson's experiments suggested the "plum pudding" model was correct – but according to the scientific method, any new theory or model should be tested by further experimentation and observation.

In the case of the "plum pudding" model, it would take a man named Ernest Rutherford to prove it wrong. Rutherford and his experiments will be the topic of the next section. Rutherford's Model of the Atom[ edit ] Disproving Thomson's "plum pudding" model began with the discovery that an element known as uranium emitted positively charged particles called alpha particles as it underwent radioactive decay. Radioactive decay occurs when one element decomposes into another element. It only happens with a few very unstable elements. This involves some difficult concepts so, for now, just accept the fact that uranium decays and emits alpha particles in the process. Alpha particles themselves didn't prove anything about the structure of the atom. In fact, a man named Ernest Rutherford (see the figure at right) proved that alpha particles were nothing more than helium atoms that had lost their electrons. Think about why an atom that has lost electrons will have a positive charge. Alpha particles could, however, be used to conduct some very interesting experiments. Rutherford's gold foil experiment. Ernest Rutherford was fascinated by all aspects of alpha particles.

For the most part, though, he seemed to view alpha particles as tiny bullets that he could use to fire at all kinds of different materials. One experiment in particular, however, surprised Rutherford, and everyone else. Rutherford found that when he fired alpha particles at a very thin piece of gold foil, an interesting thing happened. Almost all of the alpha particles went straight through the foil as if they'd hit nothing at all. Every so often, though, one of the alpha particles would be deflected slightly as if it had bounced off of something hard. Even less often, Rutherford observed alpha particles bouncing straight back at the "gun" from which they had been fired! It was as if these alpha particles had hit a wall "head-on" and had ricocheted right back in the direction that they had come from. Rutherford thought that these experimental results were rather odd. Rutherford described firing alpha particles at gold foil like shooting a high-powered rifle at tissue paper. Would you ever expect the bullets to hit the tissue paper and bounce back at you? Of course not! The bullets would break through the tissue paper and keep on going, almost as if they'd hit nothing at all.

That's what Rutherford had expected would happen when he fired alpha particles at the gold foil. Therefore, the fact that most alpha particles passed through didn't shock him. On the other hand, how could he explain the alpha particles that got deflected? Even worse, how could he explain the alpha particles that bounced right back as if they'd hit a wall? Rutherford decided that the only way to explain his results was to assume that the positive matter forming the gold atoms was not, in fact, distributed like the batter in plum pudding, but rather, was concentrated in one spot, forming a small positively charged particle somewhere in the center of the gold atom. We now call this clump of positively charged mass the nucleus. According to Rutherford, the presence of a nucleus explained his experiments, because it implied that most alpha particles passed through the gold foil without hitting anything at all. Once in a while, though, the alpha particles would actually collide with a gold nucleus, causing the alpha particles to be deflected, or even to bounce right back in the direction they came from.

Rutherford Suggested Electrons "Orbited"[ edit ] While Rutherford's discovery of the positively charged atomic nucleus offered insight into the structure of the atom, it also led to some questions. According to the "plum pudding" model, electrons were like plums embedded in the positive "batter" of the atom. Rutherford's model, though, suggested that the positive charge wasn't distributed like batter, but rather, was concentrated into a tiny particle at the center of the atom, while most of the rest of the atom was empty space. What did that mean for the electrons? If they weren't embedded in the positive material, exactly what were they doing? And how were they held in the atom? Rutherford suggested that the electrons might be circling or "orbiting" the positively charged nucleus as some type of negatively charged cloud, but at the time, there wasn't much evidence to suggest exactly how the electrons were held in the atom. Despite the problems and questions associated with Rutherford's experiments, his work with alpha particles definitely seemed to point to the existence of an atomic "nucleus". Between J. J.

Thomson, who discovered the electron, and Rutherford, who suggested that the positive charges in an atom were concentrated at the atom's center, the 1890s and early 1900s saw huge steps in understanding the atom at the "subatomic" (or smaller than the size of an atom) level. Although there was still some uncertainty with respect to exactly how subatomic particles were organized in the atom, it was becoming more and more obvious that atoms were indeed divisible. Moreover, it was clear that the pieces an atom could be separated into negatively charged electrons and a nucleus containing positive charges. In the next lesson, we'll look more carefully at the structure of the nucleus, and we'll learn that while the atom is made up of positive and negative particles, it also contains neutral particles that neither Thomson, nor Rutherford, were able to detect with their experiments. Lesson Summary[ edit ] Dalton's Atomic Theory wasn't entirely correct. It turns out that atoms can be divided into smaller subatomic particles. A cathode ray tube is a small glass tube with a cathode and an anode at one end. Cathode rays flow from the cathode to the anode.

When cathode rays hit a material known as "phosphor" they cause the phosphor to glow. J. J. Thomson used this phenomenon to reveal the path taken by a cathode ray in a cathode ray tube. J. J. Thomson found that the path taken by the cathode ray could be bent towards a positive metal plate, and away from a negative metal plate. As a result, he reasoned that the particles in the cathode ray were negative. Further experiments with magnets proved that the particles in the cathode ray also had mass. Thomson's measurements indicated, however, that the particles were much smaller than atoms. J. J. Thomson suggested that these small, negatively charged particles were actually subatomic particles. We now call them "electrons". Since atoms are neutral, atoms that contain negatively charged electrons must also contain positively charged material. According to Thomson's "plum pudding" model, the negatively charged electrons in an atom are like the pieces of fruit in a plum pudding, while the positively charged material is like the batter.

When Ernest Rutherford fired alpha particles at a thin gold foil, most alpha particles went straight through; however, a few were scattered at different angles, and some even bounced straight back. In order to explain the results of his gold foil experiment, Rutherford suggested that the positive matter in the gold atoms was concentrated at the center of the gold atom in what we now call the nucleus of the atom. Rutherford's model of the atom didn't explain where electrons were located in an atom. Decide whether each of the following statements is true or false. (a) Cathode rays are positively charged. (b) Cathode rays are rays of light, and thus they have no mass. (c) Cathode rays can be repelled by a negatively charged metal plate. (d) J.J. Thomson is credited with the discovery of the electron. (e) Phosphor is a material that glows when struck by cathode rays. Match each observation with the correct conclusion. (a) Cathode rays are attracted to a positively charged metal plate. - i. Cathode rays are positively charged. - ii. Cathode rays are negatively charged. - iii. Cathode rays have no charge. (b) Electrons have a negative charge. - i.

atoms must be negatively charged. - ii. atoms must be positively charged. - iii. atoms must also contain positive subatomic material. (c) Alpha particles fired at a thin gold foil are occasionally scattered back in the direction that they came from - i. the positive material in an atom is spread throughout like the “batter” in pudding - ii. atoms contain neutrons - iii. the positive charge in an atom is concentrated in a small area at the center of the atom. Alpha particles are: (a) Helium atoms that have extra electrons. (b) Hydrogen atoms that have extra electrons. (c) Hydrogen atoms that have no electrons. (d) Electrons. (e) Helium atoms that have lost their electrons. (f) Neutral helium atoms. What is the name given to the tiny clump of positive material at the center of an atom? Choose the correct statement. (a) Ernest Rutherford discovered the atomic nucleus by performing experiments with aluminum foil. (b) Ernest Rutherford discovered the atomic nucleus using a cathode ray tube. (c) When alpha particles are fired at a thin gold foil, they never go through. (d) Ernest Rutherford proved that the "plum pudding model" was incorrect.

(e) Ernest Rutherford experimented by firing cathode rays at gold foil. Answer the following questions: (a) Will the charges +2 and −2 cancel each other out? (b) Will the charges +2 and −1 cancel each other out? (c) Will the charges +1 and +1 cancel each other out? (d) Will the charges −1 and +3 cancel each other out? (e) Will the charges +9 and −9 cancel each other out? Electrons are ______ negatively charged metals plates and ______ positively charged metal plates? What was J. J. Thomson's name for electrons? A "sodium cation" is a sodium atom that has lost one of its electrons. Would the charge on a sodium cation be positive, negative or neutral? Would sodium cations be attracted to a negative metal plate, or a positive metal plate? Would electrons be attracted to or repelled from sodium cations? Suppose you have a cathode ray tube coated with phosphor so that you can see where on the tube the cathode ray hits by looking for the glowing spot.

What will happen to the position of this glowing spot if: (a) a negatively charged metal plate is placed above the cathode ray tube (b) a negatively charged metal plate is placed to the right of the cathode ray tube (c) a positively charged metal plate is placed to the right of the cathode ray tube (d) a negatively charged metal plate is placed above the cathode ray tube, and a positively charged metal plate is placed to the left of the cathode ray tube (e) a positively charged metal plate is placed below the cathode ray tube, and a positively charged metal plate is also placed to the left of the cathode ray tube. What is an Atom? | Parts of an Atom What is an Atom? By Tim Sharp, Reference Editor | June 5, 2013 06:22pm ET MORE Credit: general-fmv Shutterstock Atoms are the basic units of matter and the defining structure of elements. Atoms are made up of three particles: protons, neutrons and electrons. Protons and neutrons are heavier than electrons and reside in the center of the atom, which is called the nucleus. Electrons are extremely lightweight and exist in a cloud orbiting the nucleus.

The electron cloud has a radius 10,000 times greater than the nucleus. Protons and neutrons have approximately the same mass. However, one proton weighs more than 1,800 electrons. Atoms always have an equal number of protons and electrons, and the number of protons and neutrons is usually the same as well. Adding a proton to an atom makes a new element, while adding a neutron makes an isotope, or heavier version, of that atom. Nucleus The nucleus was discovered in 1911, but its parts were not identified until 1932. Virtually all the mass of the atom resides in the nucleus. The nucleus is held together by the "strong force," one of the four basic forces in nature. This force between the protons and neutrons overcomes the repulsive electrical force that would, according to the rules of electricity, push the protons apart otherwise. Protons Protons are positively charged particles found within atomic nuclei. They were discovered by Ernest Rutherford in experiments conducted between 1911 and 1919. The number of protons in an atom defines what element it is.

For example, carbon atoms have six protons, hydrogen atoms have one and oxygen atoms have eight. The number of protons in an atom is referred to as the atomic number of that element. The number of protons in an atom also determines the chemical behavior of the element. The Periodic Table of the Elements arranges elements in order of increasing atomic number. Protons are made of other particles called quarks. There are three quarks in each proton — two "up" quarks and one "down" quark — and they are held together by other particles called gluons. Electrons Electrons have a negative charge and are electrically attracted to the positively charged protons. Electrons surround the atomic nucleus in pathways called orbitals. The inner orbitals surrounding the atom are spherical but the outer orbitals are much more complicated. An atom's electron configuration is the orbital description of the locations of the electrons in an unexcited atom. Using the electron configuration and principles of physics, chemists can predict an atom's properties, such as stability, boiling point and conductivity. Typically, only the outermost electron shells matter in chemistry.

The inner electron shell notation is often truncated by replacing the long-hand orbital description with the symbol for a noble gas in brackets. This method of notation vastly simplifies the description for large molecules. For example, the electron configuration for beryllium (Be) is 1s22s2, but it's is written [He]2s2. [He] is equivalent to all the electron orbitals in a helium atom. The Letters, s, p, d, and f designate the shape of the orbitals and the superscript gives the number of electrons in that orbital. Neutrons Neutrons are uncharged particles found within atomic nuclei. A neutron's mass is slightly larger than that of a proton. Like protons, neutrons are also made of quarks — one "up" quark and two "down" quarks. Neutrons were discovered by James Chadwick in 1932. Isotopes The number of neutrons in a nucleus determines the isotope of that element. For example, hydrogen has three known isotopes: protium, deuterium and tritium.

Protium, symbolized as 1H, is just ordinary hydrogen; it has one proton and one electron and no neutrons. Deuterium (D or 2H) has one proton, one electron and one neutron. Tritium (T or 3H) has one proton, one electron and two neutrons. Related: BBC - GCSE Bitesize: Structure of the atom Next An atom is made from a nucleus surrounded by electrons. The nucleus contains protons and neutrons. Isotopes are atoms that have the same number of protons, but different numbers of neutrons. An early model of the atom was the plum pudding model. It was disproved by Rutherford's scattering experiment and replaced by the nuclear model. Structure of the atom You should be able to describe the nuclear modelnuclear model: The scientific idea that an atom has electrons surrounding a nucleus that contains protons and neutrons. of the atom [atom: All elements are made of atoms. An atom consists of a nucleus containing protons and neutrons, surrounded by electrons. ].

The nuclear model The structure of the atom Atoms contain three sub-atomic particles called protonsproton: A proton is a small particle with a positive charge found in the nucleus of the atom., neutrons and electrons [electron: An electron is a very small negatively-charged particle found in an atom in the space surrounding the nucleus. ]. The protons and neutrons are found in the nucleus at the centre of the atom. The nucleus is very much smaller than the atom as a whole. The electrons are arranged in energy levels around the nucleus. The table shows the properties of these three sub-atomic particles. Properties of sub-atomic particles BBC - GCSE Bitesize: The structure of an atom Next Atoms consist of electrons [electrons: Sub-atomic particles, with a negative charge and a negligible mass relative to protons and neutrons. ] surrounding a nucleus [nucleus: The central part of an atom. It contains protons and neutrons, and has most of the mass of the atom. ] that contains protonsprotons: Sub-atomic particles with a positive charge and a relative mass of 1.

and neutronsneutrons: Uncharged sub-atomic particles, with a mass of 1 relative to a proton.. Neutrons are neutral, but protons and electrons are electrically charged. Protons have a relative charge of +1, while electrons have a relative charge of -1. The number of protons in an atom is called its atomic number. In the periodic table atoms are arranged in atomic number order. Electrons are arranged in energy levels or shells, and different energy levels can hold different numbers of electrons. The electronic structure of an atom is a description of how the electrons are arranged, which can be shown in a diagram or by numbers. There is a link between the position of an element in the periodic table and its electronic structure. The structure of an atom Although the word 'atom' comes from the Greek for indivisible, we now know that atoms are not the smallest particles of matter. Atoms are made from smaller subatomic particles. At the centre of an atom is a nucleus [nucleus: The central part of an atom. It contains protons and neutrons, and has most of the mass of the atom.

] containing protonsprotons: Sub-atomic particles with a positive charge and a relative mass of 1. and neutronsneutrons: Uncharged sub-atomic particles, with a mass of 1 relative to a proton.. Electrons [electrons: Sub-atomic particles, with a negative charge and a negligible mass relative to protons and neutrons. ] are arranged around the nucleus in energy levels or shells. Make sure you can label a simple diagram of an atom like this one. Both protons and electrons have an electrical charge. Both have the same size of electrical charge, but the proton is positive and the electron negative. The neutron is neutral. The electrical charge of particles particle Electric Charge in the Atom About Watch and Favorite Watch Watching this resources will notify you when proposed changes or new versions are created so you can keep track of improvements that have been made. Favorite Favoriting this resource allows you to save it in the “My Resources” tab of your account. There, you can easily access this resource later when you’re ready to customize it or assign it to your students. Electric Charge in the Atom Atoms contain negatively charged electrons and positively charged protons; the number of each determines the atom's net charge.

Learning Objective Identify factors that determine the atom's net charge Key Points A proton is a positively charged particle located in the nucleus of an atom . An electron has $\frac{1}{1836}$ times the mass of a proton, but an equal and opposite negative charge. An elementary charge -- that of a proton or electron -- is approximately equal to 1.6×10-19Coulombs. Unlike protons, electrons can move from atom to atom. If an atom has an equal number of protons and electrons, its net charge is 0. If it gains an extra electron, it becomes negatively charged and is known as an anion. If it loses an electron, it becomes positively charged and is known as a cation. Term Full Text Overview of Atomic Electrical Charges Atoms, the fundamental building blocks of all molecules, consist of three types of particles: protons, neutrons, and electrons. Of these three subatomic particle types, two (protons and electrons) carry a net electric charge , while neutrons are neutral and have no net charge. Both protons and electrons have charge that is quantized. That is, the magnitude of their respective charges, which are equal each other, is 1.

This standard value is equal to approximately 1.6×10-19 Coulombs . Protons Protons are found in the center of the atom; they, with neutrons, make up the nucleus. Protons have a charge of +1 and a mass of 1 atomic mass unit, which is approximately equal to 1.66×10-24 grams. The number of protons in an atom defines the identity of the element (an atom with 1 proton is hydrogen, for example, and an atom with two protons is helium). As such, protons are relatively stable; their number rarely changes, only in the instance of radioactive decay . Electrons Electrons are found in the periphery of the atom and have a charge of -1. They are much smaller than protons; their mass is $\frac{1}{1836}$ amu. Typically in modeling atoms, protons and neutrons are regarded as stationary, while electrons move about in the space outside the nucleus like a cloud. The negatively charged electronic cloud indicates the regions of the space where electrons are likely to be found. The electrons cloud patterns are extremely complex and is of no importance to the discussion of electric charge in the atom.

More important is the fact that electrons are labile; that is, they can be transferred from one atom to the next. It is through electronic transfer that atoms become charged. Ions In the ground state , an atom will have an equal number of protons and electrons, and thus will have a net charge of 0. However, because electrons can be transferred from one atom to another, it is possible for atoms to become charged. Atoms in such a state are known as ions. If a neutral atom gains an electron, it becomes negative. This kind of ion is called an anion. If a neutral atom loses an electron, it becomes positive. This kind of ion is called a cation. The steady flow of electrons is called current . Current is what flows through electrical wires and powers electronics items, from light bulbs to televisions. atom: Structure of the Atom atom Structure of the Atom The atom consists of a central, positively charged core, the nucleus , and negatively charged particles called electrons that are found in orbits around the nucleus. The Nucleus Almost the entire mass of the atom is concentrated in the nucleus, which occupies only a tiny fraction of the atom's volume.

The nucleus of an atom consists of neutrons and protons, the neutron being an uncharged particle and the proton a positively charged one. Their masses are almost equal. Atoms containing the same number of protons but different numbers of neutrons represent different forms, or isotopes , of the same element. The Electrons Surrounding the nucleus of an atom are its electrons; for a neutral atom, the number of electrons is equal to the atomic number. The outermost electrons of an atom determine its chemical and electrical properties. An atom may combine chemically with another atom in various ways, either by giving up or receiving electrons, thus setting up an electrical attraction between the atoms (see ion ), or by sharing one or more pairs of electrons (see chemical bond ). Because metals have few outermost electrons and tend to give them up easily, they are good conductors of electricity or heat (see conduction ). The electrons are often described as revolving about the nucleus as the planets revolve about the sun. This picture, however, is misleading. The quantum theory has shown that all particles in motion also have certain wave properties. For a particle the size of an electron, these properties are of considerable importance.

As a result the electrons in an atom cannot be pictured as localized in space, but rather should be viewed as smeared out over the entire orbit so that they form a cloud of charge. The electron clouds around the nucleus represent regions in which the electrons are most likely to be found. The shapes of these clouds can be very complex, in marked contrast to the simple elliptical orbits of planets. Surprisingly, the sizes of all atoms are comparable, in spite of the large differences in the number of electrons they contain. Sections in this article: Atom Models Atom Models After reading this section you will be able to do the following: Describe the basic structure of an atom. Explain what holds an atom together. What is an atom composed of? An atom is the smallest particle of any element that still retains the characteristics of that element. However, atoms consist of even smaller particles. Atoms consist of a central, dense nucleus that is surrounded by one or more lightweight negatively charged particles called electrons. The nucleus is made up of positively charged particles called protons and neutrons which are neutral. An atom is held together by forces of attraction between the electrons and the protons. The neutrons help to hold the protons together.

Protons and neutrons are believed to be made up of even smaller particles called quarks. We will limit our discussions to protons, neutrons and electrons. Niels Bohr was a Danish scientist who introduced the model of an atom in 1913. Bohr's model consists of a central nucleus surrounded by tiny particles called electrons that are orbiting the nucleus in a cloud. These electrons are spinning so fast around the nucleus of the atom that they would be just a blur if we could see particles that small. In our pictures and exercises the electron appears to orbit in the same path around the nucleus much like the planets orbit the Sun. But, please be aware that electrons do not really orbit in the same path. The electrons actually change their orbit with each revolution. Review Atoms are composed of protons, neutrons, and electrons. The forces of attraction between the electrons and the protons hold an atom together.

Question: What is the name for the centre of an atom?
Answer: Nucleus