Atoms fundamental subatomic particles

Our modern theory of the atom describes it as an electrically neutral sphere with a tiny nucleus at the center, which holds the positively charged protons and the neutral neutrons. The negatively charged electrons move around the nucleus in complex paths, all of which comprise the electron cloud. Table 5.1 summarizes the properties of the three fundamental subatomic particles ... 

Further experiments by Rutherford and others in the period from 1910 to 1930 showed that a nucleus is composed of two kinds of particles, called protons and neutrons. Protons have a mass of 1.672 622 X 10 24g (about 1836 times greater than that of an electron) and are positively charged. Because the charge on a proton is opposite in sign but equal in size to that on an electron, the numbers of protons and electrons in a neutral atom are equal. Neutrons (1.674 927 x 10-24 g) are almost identical in mass to protons but carry no charge, and the number of neutrons in a nucleus is not directly related to the numbers of protons and electrons. Table 2.1 compares the three fundamental subatomic particles, and Figure 2.6 gives an overall view of the atom. 

The chemical master equation (CME) for a given system invokes the same rate constants as the associated deterministic kinetic model. Yet the CME is more fundamental than the deterministic kinetic view. Just as Schrodinger s equation is the fundamental equation for modeling motions of atomic and subatomic particle systems, the CME is the fundamental equation for reaction systems. Remember that Schrodinger s equation is not a model for a specific mechanical system. Rather, it is a theoretical framework upon which models for particular systems can be developed. In order to write down a model for an atomic system based on Schrodinger s equation, one needs to know how to write down the Hamiltonian a priori. Similarly, the CME is not a model for a specific biochemical reaction system it is a theoretical framework. To determine the CME model for a reaction system, one must know what are the possible elementary reactions and the associated rate constants. 

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. 

Electron i- lek- tran [electr- + -on] (1891) n. A (perhaps) fundamental subatomic particle with a very low mass and a unit negative electrical charge found in the extranuclear region of an atom. The electron is a small... 

Electron Fundamental subatomic particle with a charge of 1.602 10 C and a rest mass of 9.110 10 kg. The number and arrangement of electrons in atoms is largely responsible for the chemical properties of elements and many of their physical properties. 

This chapter emphasizes several aspects of chemistry. It begins with a brief discussion of the nature of matter and the states of matter. Next follows a discussion of the fundamental subatomic particles that make up all matter and explains how these are assembled to produce atoms. In tnm, atoms join together to make compounds. Chemical reactions and chemical equations that represent them are discussed. Solution chemistry is especially important to aquatic chemistry and is addressed in a separate section. The important, vast discipline of organic chemistry is crucial to all parts of the environment and is addressed in Chapter 20. 

The role—indeed, the existence—of quantum mechanics was appreciated only during the twentieth century. Until then it was thought that the motion of atomic and subatomic particles could be expressed in terms of the laws of classical mechanics introduced in the seventeenth century by Isaac Newton (see Fundamentals F.3), for these laws were very successful at explaining the motion of planets and everyday objects such as pendulums and projectiles. Classical physics is based on three obvious assumptions ... 

Once the particulate nature of matter began to evolve, it was a matter of time (over half a century) before a coherent arrangement of the different types of atoms based on their atomic weight began to take shape (Mendeleev [5]). A decade later, one of the fundamental subatomic particles was discovered, the electron (Crookes), but this discovery was not understood for what it was until Thomson [6]... 

The atom is the fundamental building block of matter, and consists of a collection of positive, negative, and neutral subatomic particles. 

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. 

In 1932, Rutherford s coworker, English physicist James Chadwick (1891-1974), showed that the nucleus also contained another subatomic particle, a neutral particle called the neutron. A neutron has a mass nearly equal to that of a proton, hut it carries no electrical charge. Thus, three subatomic particles are the fundamental building blocks from which all atoms are... 

The concept of the elements depended on two different but ultimately complementary ideas about matter. The first idea was ancient that the elements were the fundamental building blocks of nature. Whether there were 1, 2, 3, 4, or 92 elements was in a sense less important than the power of the concept to explain nature and direct research. The second idea came with the discovery of the structure of the atom and the physics that made that discovery possible that an element represented a specific combination of subatomic particles determined by physical laws. The creation of controlled nuclear fission and the invention of accelerators and cyclotrons made a kind of modem alchemy possible, allowing the creation of new elements that were not found in nature but that still met the new conditions to be considered elements. 

Fermi, Enrico. (1901-1954). An Italian physicist who later became a U.S. citizen. He developed a statistical approach to fundamental problems of physical chemistry based on Pauli s exclusion principle. He discovered induced or artificial radioactivity resulting from neutron impingement, as well as slow or thermal neutrons. He was professor of physics at Columbia (1939) and awarded the Nobel Prize in physics in 1938. He was the first to achieve a controlled nuclear chain reaction, directed the construction of the first nuclear reactor at the University of Chicago (1942), and worked on the atomic bomb at Los Alamos. He also carried on fundamental research on subatomic particles using sophisticated statistical techniques. Element 100 (fermium) is named after him. 

Many other subatomic particles, such as quarks, positrons, neutrinos, pions, and muons, have also been discovered. It is not necessary to study their characteristics to learn the fundamentals of atomic structure that are important in chemical reactions. 

An atom is the fundamental unit of matter. In ordinary chemical reactions, atoms cannot be created or destroyed. Atoms contain smaller subatomic particles protons, neutrons, and electrons. Protons and neutrons are located in the nucleus, or center, of the atom and are referred to as nucleons. Electrons are located outside the nucleus. Protons and neutrons are comparable in mass and significantly more massive than electrons. Protons carry positive electrical charge. Electrons carry negative charge. Neutrons are electrically neutral. 

Figure 2.7 shows the location of the elementary particles (protons, neutrons, and electrons) in an atom. There are other subatomic particles, but the electron, the proton, and the neutron are the three fundamental components of the atom that are important in chemistry. Table 2.1 shows the masses and charges of these three elementary particles. 

Of course, we recognize that progress in health is utterly dependent upon science and that ultimately all science, at least all natural science, springs from a common base. No research is so fundamental that we can say that it does not have and never will have relevance to health. Nevertheless, we must recognize a level sufficiently remote from biomedical research that its present contributions can have little if any import for the foreseeable future. For example, current work in subatomic particle physics is unlikely to have an early influence, despite the tremendous importance in biomedical research of the atomic physics of a generation ago. Few people would expect the NIH to support work in present-day atomic physics. 

Protons and neutrons each contain three quarks. A neutron consists of one up quark and two down quarks. A proton consists of two up quarks and one down quark. Other quarks are named strange, charm, bottom, and top., but these four are not part of atoms. Quarks are a fundamental constituent of matter according to current standard model of particle physics, but individual quarks are not seen. Instead they are always confined within other subatomic particles. There is no need to consider quarks when describing chemical interactions. Only electrons are involved in chemical reactions. The position and sizes of these particles in a helium atom is indicated in the diagram at right. A diagram... 

Quantum Mechanics Physical analysis at the level of atoms or subatomic fundamental particles. 

It is not possible to state the absolute mass or weight of any material object. At the most fundamental level, one can only state that a hydrogen atom has the mass of a single proton and a single electron it is impossible to know the absolute masses of those subatomic particles. This basic relationship, however, provides the means whereby other atoms can be... 

Extensive experimental evidence collected since the middle of the 19th century indicates that atoms are made up of many smaller particles. More than 100 of these subatomic particles have been discovered, and the search for more continues. As yet there is no single theory that can explain all observations involving subatomic particles, but three fundamental particles are included in all current theories the proton, the neutron, and the electron. Most chemical behavior of matter can be explained in terms of a few of the well-known characteristics of these particles. These important characteristics are mass, electrical charge, and location in atoms. They are summarized in > Table 2.3. The atomic mass unit (u) shown in the table is discussed in Section 2.4. 

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