Electrons, Protons, and Neutrons

Although an atom is an unimaginably small particle, still smaller particles make up atoms the subatomic particles. Three fundamental subatomic particles have been characterized during the last 130 years the electron, the proton, and the neutron. The electron and proton bear opposite electrical charge negative and positive, respectively. The neutron bears no charge, as its name (from the same root as neutral ) implies. 

There are only two kinds of electrical charge negative (-) and positive (+). Opposite charges 

Just as the sizes of the charge on the electron and proton have been reduced to a convenient 1 -and 1 +, the extremely small masses of the three subatomic particles are often stated in atomic mass units (amu) to bring the mass of the proton and neutron numerically close to 1. One amu = 1.6606 x 10 24 g. The mass in both grams and amu for the three subatomic particles is given in the following table. 

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Electrons, protons and neutrons and all other particles that have s = are known as fennions. Other particles are restricted to s = 0 or 1 and are known as bosons. There are thus profound differences in the quantum-mechanical properties of fennions and bosons, which have important implications in fields ranging from statistical mechanics to spectroscopic selection mles. It can be shown that the spin quantum number S associated with an even number of fennions must be integral, while that for an odd number of them must be half-integral. The resulting composite particles behave collectively like bosons and fennions, respectively, so the wavefunction synnnetry properties associated with bosons can be relevant in chemical physics. One prominent example is the treatment of nuclei, which are typically considered as composite particles rather than interacting protons and neutrons. Nuclei with even atomic number tlierefore behave like individual bosons and those with odd atomic number as fennions, a distinction that plays an important role in rotational spectroscopy of polyatomic molecules. 

Quantum mechanics is primarily concerned with atomic particles electrons, protons and neutrons. When the properties of such particles (e.g. mass, charge, etc.) are expressed in macroscopic units then the value must usually be multiplied or divided by several powers of 10. It is preferable to use a set of units that enables the results of a calculation to he reported as easily manageable values. One way to achieve this would be to multiply eacli number by an appropriate power of 10. However, further simplification can be achieved by recognising that it is often necessary to carry quantities such as the mass of the electron or electronic charge all the way through a calculation. These quantities are thus also incorporated into the atomic units. The atomic units of length, mass and energy are as follows ... 

The three particles that make up atoms are protons, neutrons, and electrons. Protons and neutrons are heavier than electrons and reside in the "nucleus," which is the center of the atom. Protons have a positive electrical charge, and neutrons have no electrical charge. Electrons are extremely lightweight and are negatively charged. They exist in a cloud that surrounds the atom. The electron cloud has a radius 10,000 times greater than the nucleus. 

A representation of atomic structure. The various spheres are not drawn to scale. The lump of iron on the left would contain almost a million million million million (10 ) atoms, one of which is represented by the sphere in the top center of the page. In turn, each atom is composed of a number of electrons, protons, and neutrons. For example, an atom of the element iron contains 26 electrons, 26 protons, and 30 neutrons. The physical size of the atom is determined mainly by the number of electrons, but almost all of its mass is determined by the number of protons and neutrons in its dense core or nucleus (lower part of figure). The electrons are spread out around the nucleus, and their number determines atomic size but the protons and neutrons compose a very dense, small core, and their number determines atomic mass. 

With only 90 elements, one might assume that there could be only about 90 different substances possible, but everyday experience shows that there are millions of different substances, such as water, brick, wood, plastics, etc. Indeed, elements can combine with each other, and the complexity of these possible combinations gives rise to the myriad substances found naturally or produced artificially. These combinations of elemental atoms are called compounds. Since atoms of an element can combine with themselves or with those of other elements to form molecules, there is a wide diversity of possible combinations to make all of the known substances, naturally or synthetically. Therefore, atoms are the simplest chemical building blocks. However, to understand atoms, it is necessary to examine the structure of a typical atom or, in other words, to examine the building blocks of the atoms themselves. The building blocks of atoms are called electrons, protons, and neutrons (Figure 46.1). 

Liquid Helium-4. Quantum mechanics defines two fundamentally different types of particles bosons, which have no unpaired quantum spins, and fermions, which do have unpaired spins. Bosons are governed by Bose-Einstein statistics which, at sufficiently low temperatures, allow the particles to coUect into a low energy quantum level, the so-called Bose-Einstein condensation. Fermions, which include electrons, protons, and neutrons, are governed by Fermi-DHac statistics which forbid any two particles to occupy exactly the same quantum state and thus forbid any analogue of Bose-Einstein condensation. Atoms may be thought of as assembHes of fermions only, but can behave as either fermions or bosons. If the total number of electrons, protons, and neutrons is odd, the atom is a fermion if it is even, the atom is a boson. 

Finally we have quantum mechanics, which normally has to be invoked when dealing with situations where small particles (such as electrons, protons and neutrons) are involved. 

At the present time, quarks are believed to be elementary particles. All the particles in an atom, whether elementary or not, are particles of matter and possess mass. Electrons, protons, and neutrons can also exist outside of atoms. 

Our picture of atomic architecture is now compiete. Three kinds of particles—electrons, protons, and neutrons-combine in various numbers to make the different atoms of aii the eiements of the periodic table. Table 2-1 summarizes the characteristics of these three atomic buiiding biocks. 

Heisenberg s uncertainty principle forced a change in thinking about how to describe the universe, hi a universe subject to uncertainty, many things cannot be measured exactly, and it is never possible to predict with certainty exactly what will occur next. This uncertainty has become accepted as a fundamental feature of the universe at the scale of electrons, protons, and neutrons. 

Every type of particle has a specific unique value of s, which is called the spin of that particle. The particle may be elementary, such as an electron, or composite but behaving as an elementary particle, such as an atomic nucleus. All He nuclei, for example, have spin 0 all electrons, protons, and neutrons... 

Since electrons, protons, and neutrons are the fundamental constituents of atoms and molecules and all three elementary particles have spin one-half, the case 5 = I is the most important for studying chemical systems. For s = there are only two eigenfunctions,, d) and j, — ). For convenience, the state s =, ms = is often called spin up and the ket, is written as t) or as a). Likewise, the state s =, m = is called spin down with the ket j, — ) often expressed as J,) or /3). Equation (7.6) gives... 

As pointed out in Section 7.2, electrons, protons, and neutrons have spin f. Therefore, a system of N electrons, or N protons, or N neutrons possesses an antisymmetric wave function. A symmetric wave function is not allowed. Nuclei of " He and atoms of " He have spin 0, while photons and nuclei have spin 1. Accordingly, these particles possess symmetric wave functions, never antisymmetric wave functions. If a system is composed of several kinds of particles, then its wave function must be separately symmetric or antisymmetric with respect to each type of particle. For example, the wave function for... 

Most particles of interest to physicists and chemists are found to be antisymmetric under permutation. They include electrons, protons and neutrons, as well as positrons and other antiparticles These particles, which are known as Fermions, all have spins of one-half. The relation between the permutation symmetry and the value of the spin has been established by experiment and, in the case of the electron, by application of relativistic quantum theory. 

Our goal for this chapter is to help you to learn about electrons and the current models for where those electrons are located within the atom. You may want to briefly review Chapter 2 concerning electrons, proton, and neutrons. Your text will probably have some nice pictures of orbitals, so when you get to the section on quantum numbers and orbitals, you might want to have your text handy. And don t forget to Practice, Practice, Practice. 

It is a fundamental property of atomic particles, such as electrons, protons, and neutrons, to have spins. Spins can be classified as + or spin. For example, a deuterium atom, H, has one unpaired electron, one unpaired proton, and one unpaired neutron. The total nuclear spin = j (from the proton) + j (from the neutron) = 1. Hence, the nuclear spins are paired and result in no net spin for the nucleus. For atoms such as H,... 

The science of particle physics continues to study electrons, protons, and neutrons, which are considered subatomic particles. The quest continues for even smaller subatomic, or rather subnuclear, particles. Most subnuclear particles are fleeting in time of existence, are practically weightless, and are thus very difficult to detect and measure. 

This means that a small = 2, 7-D lattice (2X2X2X2X2X2X2) can hold the 1,830 varieties of fleas An = 9 hyperlattice in the fiftieth dimension can hold each electron, proton, and neutron in the universe (each particle in its own cage). 

Today, the results of many scientific experiments confirm the atomic nature of matter. Contrary to Daltons notion of the indivisible atom, however, an accumulation of evidence tells us that atoms are in fact divisible and that they are made of smaller particles called electrons, protons, and neutrons. For the remainder of this chapter, we explore these subatomic particles in detail, continuing with our historical perspective. 

The total mass of an atom is called its atomic mass. This is the sum of the masses of all the atom s components (electrons, protons, and neutrons). Because electrons are so much less massive than protons and neutrons, their contribution to atomic mass is negligible. As we explore further in Section 9.2, a special unit has been developed for atomic masses. This is the atomic mass unit, amu, where 1 atomic mass unit is equal to 1.661 X 10-24 gram, which is slightly less than the mass of a single proton. As shown in Figure 3.21, the atomic masses listed in the periodic table are in atomic mass units. As is explored in the Calculation Corner on page 95, the atomic mass of an element as presented in the periodic table is actually the average atomic mass of its various isotopes. 

The atom was once thought to be the smallest unit of matter, but was then found to be composed of electrons, protons, and neutrons. The question arises are electrons, protons, and neutrons made of still smaller particles In the same way that Rutherford was able to deduce the atomic nucleus by bombarding atoms with alpha particles (Chapter 3), evidence for the existence of many other subatomic particles has been obtained by bombarding the atom with highly energetic radiation.This research over the past centmy has evolved into what is known as the "standard model of fundamental particles, which places all constituents of matter within one of two categories quarks and leptons. 

The chemists of the nineteenth century once thought that all material substances were comprised of only 36 elements,3 Over the years, these expanded to over 100 elements. Fifty years ago, it was proclaimed that the elements were made of electrons, protons, and neutrons. Then, commencing in the 1940s, many other particles were found, as described here. Then for a while it seemed that elementary matter could be reduced to three particles—the quarks. But quarks have multiplied in number, with a sixth quark now seriously proposed. Will there be too many quarks Perhaps hypothetical particles will be proposed from which the quarks are comprised. Possibly the ultimate answer will lie with the mathematical groups that order the particles rather than in truly elementary objects. ... 

Atoms are made up of subatomic particles called electrons, protons, and neutrons. 

V- Barrie M. Peake, "The Discov-U ery of the Electron, Proton, and Neutron," /. Chem. Educ.,... 

However, in the last hundred years or so it has been proved by great scientists, such as Niels Bohr, Albert Einstein, Henry Moseley, Joseph Thomson, Ernest Rutherford and James Chadwick, that atoms are in fact made up of even smaller sub atomic particles. The most important of these are electrons, protons and neutrons, although 70 sub atomic particles have now been discovered. 

The number of electrons, protons and neutrons in the atoms of some elements. 

The ultimate structures or components of reality (top) are subatomic particles, when I was a high school student, only a few such particles were known and many scientists thought that electrons, protons, and neutrons were the basics whose arrangement in patterns accounted for the way the world was. Now literally hundreds of subatomic particles have been "discovered." The word is enclosed in quotation marks because, of course, no one has actually ever seen a subatomic particle. They are assumed to exist because their presence enables sensible interpretation of various kinds of instrumental readings. Thus modern physicists picture the universe as composed of hundreds of subatomic particles being influenced by three basic types of forces (1) the nuclear binding forces, which operate only at the extremely tiny distances inside atomic nuclei i i - uis pi... 

Matter is made of particles. Some particles are atoms that contain subatomic particles, called electrons, protons, and neutrons other particles are molecules that are made up of atoms. 

Atoms are made of smaller particles. These smaller particles are electrons, protons, and neutrons. Electrons are negatively charged and they spin around the nucleus. The nucleus is the center of the atom and contains protons and neutrons. Protons are positively charged and neutrons have no charge. 

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