The Properties of Protons, Neutrons, and Electrons

Rutherford s nuclear theory was a success and is still valid today. The revolutionary part of this theory is the idea that matter—at its core—is much less uniform than it appears. If the nucleus of the atom were the size of tiiis dot , the average electron would be about 10 m away. Yet the dot would contain almost the entire mass of the atom. Imagine what matter would be like if atomic structure broke down. What if matter were composed of atomic nuclei piled on top of each other like marbles Such matter would be incredibly dense a single grain of sand composed of solid atomic nuclei would have a mass of 5 million kg (or a weight of about 10 million lb). Astronomers believe that black holes and neutron stars are composed of this kind of incredibly dense matter. 

In this model, 99.9% of the atom s mass is concentrated in a small, dense nucleus that contains protons and neutrons. The rest of the volume of the atom is mostly empty space occupied by negatively charged electrons. The number of electrons outside the nucleus is equal to the number of protons inside the nucleus. In this image, the nucleus is greatly enlarged and the electrons are portrayed as particles. 

Nuclear model— volume of atom is mostly empty space. 

Protons and neutrons have very similar masses. In SI units, the mass of the proton is 1.67262 X 10 kg, and the mass of the neutron is a close 1.67493 X 10 kg. A more common unit to express these masses, however, is the atomic mass unit (amu), defined as one-twelfth of the mass of a carbon atom containing six protons and six neutrons. In this unit, a proton has a mass of 1.0073 amu and a neutron has a mass of 1.0087 amu. Electrons, by contrast, have an almost negligible mass of 0.00091 X 10 kg, or approximately 0.00055 amu. 

CAN YOU ANSWER THIS Use the jungle gym analogy to explain why most of Rutherford s alpha-particles went right through the gold foil and why a few bounced back. Remember that his gold foil was extremely thin. 

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The proton, p, has a mass of 1.007277 u and a unit charge of +1. This charge is equal to 1.6022 x 10 19 coulombs a coulomb is the amount of electrical charge involved in a flow of electrical current of 1 ampere for 1 sec. The neutron, n, has no electrical charge and a mass of 1.008665 u. The proton and neutron each have a mass of essentially 1 u and are said to have a mass number of 1. (Mass number is a useful concept expressing the total number of protons and neutrons, as well as the approximate mass, of a nucleus or subatomic particle.) The electron, e, has an electrical charge of -1. It is very light, however, with a mass of only 0.000549 u, about 1/1840 that of the proton or neutron. Its mass number is 0. The properties of protons, neutrons, and electrons are summarized in Table 1.1. 

Quantum mechanics (or wave mechanics) is composed of certain vital principles derived from fundamental assumptions describing the natural phenomena efifeetively. The properties of protons, neutrons and electrons are adequately explained imder quantum mechanics. The electronie features of the molecules responsible for chemical alterations form the basis of drug molecule phenomena. 

The electron, e, has an electrical charge of -1. It is very light, however, with a mass of only 0.00054859 u, about 1/1840 that of the proton or neutron. Its mass number is 0. The properties of protons, neutrons, and electrons are summarized in Table 3.1. 

The Properties of Protons, Neutrons, and Electrons 97 4.7 Ions Losing and Gaining Electrons 106 ... 

If you had a sample of matter—even a tiny sample, such as a sand grain—that was composed of only protons or only electrons, the forces around that matter would be extraordinary, and the matter would be unstable. Fortunately, matter is not that way—protons and electrons exist together, canceling each other s charge and making matter charge-neutral. Table 4.1 summarizes the properties of protons, neutrons, and electrons. 

Identify the features of fhe nucleus of an atom, and discuss the properties of protons, neutrons, and electrons. 

Describe the important properties of protons, neutrons, and electrons. 

In the present state of the universe, only a very small part of the energy is in the form of protons, neutrons and electrons that make up ordinary matter in all the galaxies. The rest consists of thermal radiation at a temperature of about 2.8 K and particles called neutrinos that interact very weakly with other particles. The small amount of matter which is in the form of stars and galaxies, however, is not in thermodynamic equilibrium. The affinities for the reactions that are currently occurring in the stars are not zero. The nuclear reactions in the stars produce all the known elements from hydrogen [2-4]. Hence the observed properties such as the abundance of elements in stars and planets cannot be described using the theory of chemical equilibrium. A knowledge of the rates of reaction and the history of the star or planet are necessary to understand the abundance of elements. 

Every chemical element displayed in the Periodic Table has distinctive chemical properties because atoms are made up of protons, neutrons, and electrons, which are fermions. The Pauli exclusion principle requires that no two electrons, Hke all antisocial fermions, can occupy the same quantum state. Thus, electrons bound to nuclei making up atoms exist in an array of shells that allow all the electrons to exist in their own individual quantum state. The shell structures differ from atom to atom, giving each atom its unique chemical and physical properties. 

Particles in an Atom Atoms are composed of protons, neutrons and electrons. These are known as fundamental sub-atomic particles. The following table compares the properties of these particles. 

The smallest unit having the chemical properties of the element are the atoms. All atoms are made up from a number of elementary particles known as the protons, neutrons, and electrons. The protons and neutrons make up an atomic nucleus at the center of the atom, while the electrons, distributed in electron shells, surround the atomic nucleus. The atoms of each element are identical to each other but differ from those of other elements in atomic number (the number of protons in the atomic nucleus) and atomic weight (their weighted average mass) as listed in the table below. 

Determine the arrangement and structure of subatomic particles in atoms. Protons, neutrons, and electrons play a central role in everything chemistry, and you find their most basic properties in this part. 

The principle that governs the periodic properties of atomic matter is the composition of atoms, made up of integral numbers of discrete sub-atomic units - protons, neutrons and electrons. Each nuclide is an atom with a unique ratio of protonsmeutrons, which defines a rational fraction. The numerical function that arranges rational fractions in enumerable order is known as a Farey sequence. A simple unimodular Farey sequence is obtained by arranging the fractions (n/n+1) as a function of n. The set of /c-modular sequences ... 

The term atom and the names of its constituents—protons, neutrons, and electrons—have become almost household words during the last decade. The schematic sketch of the solar-system atom with a nucleus at the center and electrons revolving about it in circular or elliptical orbits has become as familiar as many of the commercial trademarks. This picture of the atom is that which is often presented to the student during his early chemistry courses while such a picture fits a number of important properties of atoms, it is no longer regarded as a good approximation. 

Atoms themselves are made up of even smaller particles. These subatomic particles are protons, neutrons, and electrons. Protons and neutrons cluster together to form the central core, or nucleus, of an atom. Fast-moving electrons occupy the space that surrounds the nucleus of the atom. As their names imply, subatomic particles are associated with electrical charges. Table 2.1 and Figure 2.2 summarize the general features and properties of an atom and its three subatomic particles. 

The atom is composed of many types of subatomic particles, but only three types will be important in this course. Protons and neutrons exist in the atom s nucleus, and electrons exist outside the nucleus. The nucleus (plural, nuclei) is incredibly small, with a radius about one ten-thousandth of the radius of the atom itself. (If the atom were the size of a car, the nucleus would be about the size of the period at the end of this sentence.) The nucleus does not change during any ordinary chemical reaction. (Nuclear reactions are described in Chapter 21.) The protons, neutrons, and electrons have the properties listed in Table 3.1. These properties are independent of the atom of which the subatomic particles are a part. Thus, the atom is the smallest unit that has the characteristic composition of an element, and in that sense, it is the smallest particle of an element. 

In Chapter 3, we learned that atoms owe their characteristics to their subatomic particles— protons, neutrons, and electrons. Electrons occur in regions of space outside the nucleus, and the electronic structure is responsible for all of the atom s chemical properties and many of its physical properties. The number of electrons in a neutral atom is equal to the number of protons in the nucleus. That simple description enables us to deduce much about atoms, especially concerning their interactions with one another (Chapter 5). However, a more detailed model of the atom enables even fuller explanations, including the reason for the differences between main group elements and elements of the ttansition and inner transition series. 

The subatomic particles that are the major components of the atom were introduced in Section 3.3. Protons, neutrons, and electrons have the properties presented in Table 21.1. The atomic number of an atom is the number of protons in its nucleus, and the mass number of an atom is the number of protons plus neutrons in the atom s nucleus. Isotopes are atoms having the same number of protons (the same atomic number) and different numbers of neutrons (and therefore different mass numbers). 

If one has differentiated information about elementary particles like protons, neutrons and electrons which connect to questions of chemical bonding, misconceptions can arise which mix bent water molecules or the 11-protons nucleus of a sodium atom with macroscopic characteristics of matter (see also Sect. 4.3). Since electrons are not ordinary basic particles of matter in the sense of atoms, ions and molecules, but are recognized more as charged clouds, orbital or through the particle-wave duality, the mixing of macroscopic and sub-microscopic characteristic properties should be avoided more carefully. 

Speculations about the nature of matter date back to ancient Greek philosophers like Thales, who lived in the sixth century b.c.e., and Democritus, who lived in the fifth century b.c.e., and to whom we credit the first theory of atoms. It has taken two and a half millennia for natural philosophers and, more recently, for chemists and physicists to arrive at a modern understanding of the nature of elements and compounds. By the 19th century, chemists such as John Dalton of England had learned to define elements as pure substances that contain only one kind of atom. It took scientists like the British physicists Joseph John Thomson and Ernest Rutherford in the early years of the 20th century, however, to demonstrate what atoms are—entities composed of even smaller and more elementary particles called protons, neutrons, and electrons. These particles give atoms their properties and, in turn, give elements their physical and chemical properties. 

Skill 1.2c-lllustrate the position and describe the properties of quarks, protons, neutrons, and electrons within atoms... 

At the present time, all experimental evidence indicates that nuclei consist of neutrons and protons, which are particles known as nucleons. Nuclei then consist of nucleons. Some of the properties of a neutron, a proton, and an electron, for comparison, are listed in Table 3.2. A free proton—outside the nucleus—will eventually pick up an electron and become a hydrogen atom, or it may be absorbed by a nucleus. A free neutron either will be absorbed by a nucleus or will decay according to the equation... 

We can now see why atomic weight broadly correlates with the periodicity of the kingdom, and also why it sometimes fails. First, we need to note that many properties of an element are determined by the number and arrangement of the electrons surrounding the nucleus, for these are easily rearranged and some can be stripped away. Because the electric charge of an atom is zero, the number of its electrons must be equal to the number of protons in its nucleus. We can therefore speculate that there is a link between the properties of an element and its atomic number. But the number of neutrons in a nucleus increases in step with, if a little in advance of, the number of protons. It follows that as the number of electrons increases, so too does the total number of protons and neutrons, which is what determines the mass of an atom. Hence there is a correlation between an element s atomic mass and its properties (its number of electrons). 

Atomic theory basically states that atoms are the basic, smallest building units of matter. Atoms themselves are made from protons, neutrons, and electrons. The nucleus of the atom is very small in relationship to the atom and much of the atom is actually empty space. The nucleus is the positively charged component of the atom and the neutron has a zero charge. Electrons circle the proton and carry a negative charge. If you break an atom into its smaller parts, you lose the property of the element. 

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