Physics
Electron Theory
The electron theory is a fundamental concept in physics that explains the behavior of electrons in atoms and materials. It describes how electrons move within an atom's energy levels and how they contribute to electrical conductivity and other properties of matter. This theory forms the basis for understanding phenomena such as electricity, magnetism, and chemical bonding.
Written by Perlego with AI-assistance
Related key terms
1 of 5
12 Key excerpts on "Electron Theory"
eBook - PDFElectronic Devices and Circuits
The Commonwealth and International Library: Electrical Engineering Division, Volume 1
- G. J. Pridham, N. Hiller(Authors)
- 2016(Publication Date)
- Pergamon(Publisher)
CHAPTER 3 Basic Physical Theory ELECTRONICS may be defined as the study of the motion of charged particles. This chapter considers the relation of these particles to an atomic structure of elements and their movement under the action of electric and magnetic fields. 3.1. The Atom The atom of any element is the smallest particle of that element capable of taking part in a chemical reaction. It may be regarded as being composed of electrons moving in circular or elliptical orbits about a relatively heavy nucleus of protons and neutrons as shown in Fig. 3.1. This model of the atom was proposed by Bohr Electrons Protons and jieutrons FIG. 3.1. Structure of the atom. in 1913 and although it has been displaced by later models, for many purposes it is a convenient representation to show the action of electronic devices. 87 88 ELECTRONIC DEVICES AND CIRCUITS Electrons have a mass of 9 x l 0 3 1 k g and carry a negative charge of 1-6 x 10 19 coulombs, while protons have an equal posi-tive charge but a mass 1838 times as great. Neutrons are about the same mass as protons but carry no charge. All atoms are about the same size, approximately 10 10 m dia-meter, while the nucleus is about 10 15 m in diameter. The nuclei of the heavier elements provide a greater attractive force on the orbital electrons and constrict the electrons within approximately the same atomic volume. The atomic number of an element is decided by the number of protons in the nucleus while the atomic weight is governed by the number of protons and neutrons. 3.2. Electron Orbits The position and shape of the electron orbits were derived by Bohr, who applied Planck's Quantum Theory to atomic structure. This theory states that the energy of a body can only change by definite units of energy known as quanta, and by applying this idea to the production of light by gas discharge tubes Bohr showed that definite electron energy levels existed.
eBook - PDFElectronic Devices and Circuits
The Commonwealth and International Library: Electrical Engineering Division, Volume 1
- G.J. Pridham, N. Hiller(Authors)
- 2013(Publication Date)
- Pergamon(Publisher)
C H A P T E R 3 Basic Physical Theory ELECTRONICS may be defined as the study of the motion of charged particles. This chapter considers the relation of these particles to an atomic structure of elements and their movement under the action of electric and magnetic fields. 3.1. The Atom The atom of any element is the smallest particle of that element capable of taking part in a chemical reaction. It may be regarded as being composed of electrons moving in circular or elliptical orbits about a relatively heavy nucleus of protons and neutrons as shown in Fig. 3.1. This model of the atom was proposed by Bohr ^ ~~~ Ζ><Γ / ^ ^ / ^ -E l e c t r o n s V' © ]?< Protons and neutrons F I G . 3.1. Structure of the atom. in 1913 and although it has been displaced by later models, for many purposes it is a convenient representation to show the action of electronic devices. 87 88 ELECTRONIC DEVICES AND CIRCUITS Electrons have a mass of 9 χ 1 0 3 1 kg and carry a negative charge of 1-6 χ 1 0 1 9 coulombs, while protons have an equal posi-tive charge but a mass 1838 times as great. Neutrons are about the same mass as protons but carry no charge. All atoms are about the same size, approximately 1 0 1 0 m dia-meter, while the nucleus is about 1 0 1 5 m in diameter. The nuclei of the heavier elements provide a greater attractive force on the orbital electrons and constrict the electrons within approximately the same atomic volume. The atomic number of an element is decided by the number of protons in the nucleus while the atomic weight is governed by the number of protons and neutrons. 3.2. Electron Orbits The position and shape of the electron orbits were derived by Bohr, who applied Planck's Quantum Theory to atomic structure. This theory states that the energy of a body can only change by definite units of energy known as quanta, and by applying this idea to the production of light by gas discharge tubes Bohr showed that definite electron energy levels existed.
eBook - PDFThe Physical Basis of Electronics
An Introductory Course
- D. J. Harris, P. N. Robson, P. Hammond(Authors)
- 2013(Publication Date)
- Pergamon(Publisher)
3. Fundamentals of Solid State Electronics 3 . 1 . T H E S T R U C T U R E O F T H E A T O M IN THIS chapter the motion of electrons within a solid is considered, rather than, as in the previous chapter, the motion of electrons in free space after they have been emitted from a hot cathode. In the earlier chapter the motion of an electron under the influence of electric and magnetic fields was con-sidered, and it has been assumed, as is the case in most thermionic valves, that collisions between electrons and neutral molecules or positive ions are very infrequent. In solids, however, the reverse is true. Electrons moving about in the material make many collisions with atoms of the material, and their motion is profoundly affected by these collisions. It is necessary first of all to discover why materials, classed as conductors or semiconduc-tors, possess electrons which can move from atom to atom. 3.1.1. Bohr Model of the Atom The model of the atom to be discussed was proposed in 1913 by Niels Bohr. This model has now been superseded by what is[known as the quan-tum mechanical or wave mechanical model of the atom, but the simpler Bohr model will suffice for our present considerations. The atom is considered to consist of a positively charged nucleus and a number of negatively charged electrons revolving around the nucleus in circular orbits. The nucleus consists of neutral particles called neutrons, and a number of positively charged particles called protons. The mass of a proton is 1-67X10 27 kg and its charge e is 1-60X10 19 C. The number of protons Ζ possessed by the nucleus of an atom is called the atomic num-ber of that atom. An atom is normally neutral and since the electronic 3* 2 3 24 The Physical Basis of Electronics charge — e is — 1·60χ10~ 19 C, it ^follows that a neutral atom possesses the same number of protons as electrons.
eBook - PDFSemiconductor Statistics
International Series of Monographs on Semiconductors
- J. S. Blakemore, Heinz K. Henisch(Authors)
- 2013(Publication Date)
- Pergamon(Publisher)
PART I. SEMICONDUCTORS IN THERMAL EQUILIBRIUM This page intentionally left blank Chapter 1 BASIC CONCEPTS IN THE Electron Theory OF SOLIDS 1.1 CLASSICAL THEORIES OF METALLIC CONDUCTION CONSIDERABLE insight into the nature and behavior of semiconductors (and metals) comes from an examination of the band theory of solids. This theory can be regarded as arising naturally from the broadening of the discrete quantized energy levels of an isolated atom, but it is also useful to observe the development of band theory from the so-called collective electron point of view. We accordingly start with a review of the classical and quantized free electron models of metallic conduction. This discussion serves to introduce in historical sequence the important ideas which led to the band model and to an explanation of the dis-tinction between metals, semiconductors and insulators. 1.1.1 DRUDE'S MODEL Not long after the discovery of the electron, the suggestion was first made that the outer electrons of each atom in a metal might not be tightly bound to their individual atomic cores, but might rather form a free electron gas, collectively owned by the entire set of atoms which make up a crystal. That electrons should be free to move anywhere in a crystal seems reasonable in view of the validity of Ohm's law; and that their density might be comparable with that of atoms is indicated by the very large electrical and thermal conductivities of metals. Drude (1904:1) investigated the consequences of a simple model in which all the free electrons moved with a classical momentum p = (3mokT) 1/2 and were presumed to be scattered in random directions 3 4 THE Electron Theory OF SOLIDS by the positive ion cores. The model did not have any features from which the absolute strength of this scattering could be determined, thus conductivities could be quoted only in relative terms.
eBook - PDF- Md Nazoor Khan, Simanchala Panigrahi(Authors)
- 2017(Publication Date)
- Cambridge University Press(Publisher)
10 Electronic Theory of Solids 10.1 Introduction Many physical properties of solids can be understood with help of the free electron model. According to this model, the valance electrons of the constituent atoms become conduction electrons and move freely throughout the solid. The aggregates of free electrons constitute an electron gas or electron cloud. The interpretation of properties of solids by the free electron model was developed long before the advent of quantum physics, a versatile tool of physical science. The classical theory has several conspicuous successes. However, as it is natural, the simplicity of the theory puts limitation on its success. Many properties of solids like specific heats, magnetic susceptibility of solids, superconductivity and the like cannot be explained by the classical theory of free electron model. With the advent of quantum physics, almost all the properties of solids could be explained in minute detail. Here the electron gas is subjected to Pauli’s exclusion principle and Fermi–Dirac statistics instead of Maxwell–Boltzmann statistics as in classical theory. This new formulation constitutes the quantum theory of free electrons. The free electron model of metals gives us a good insight into the heat capacity, thermal and electrical conductivity, susceptibility and electrodynamics of metals. However, the model fails to explain the distinction between metals, semi-metals (materials with a very small overlap between the bottom of the conduction band and the top of the valence band), semiconductors and insulators; the occurrence of positive values of Hall coefficient; the relation between conduction electrons in the metal and the valence electrons of free atoms and many transport properties of solids. The band theory of solids, a simple theory, then was developed to account for all these facts. We shall apply these theories to explain a few properties of solids in detail as far as the scope of this book permits.
eBook - PDFElectronic Devices and Circuits
The Commonwealth and International Library: Electrical Engineering Division, Volume 3
- G. J. Pridham, N. Hiller(Authors)
- 2016(Publication Date)
- Pergamon(Publisher)
CHAPTER 2 Basic Physical Theory IN THIS chapter the qualitative explanation of the physical proper-ties of solids discussed in previous volumes will be extended and a more quantitative approach developed. The application to pn junctions and practical devices will be considered in the next chapter. 2.1. Electronic Structure of Matter All atoms may be regarded as being composed of electrons rotating in circular or elliptical orbits about the nucleus of protons and neutrons. The simplest case is the hydrogen atom with one electron rotating in a circular orbit about a proton. The radius of this orbit may be determined by using Bohr's basic assumption regarding any electron orbit. This assumption is that the angular momentum in any stable orbit must be an integral number of h/2jt, where h is Planck's constant. Thus if the moment of inertia of an electron is / and its angular velocity is co, nh 2n where n is an integer, 2 v nh where m e is the mass of an electron in kg, r is its distance from the 60 BASIC PHYSICAL THEORY 61 nucleus in metres, and v its velocity in metres per second. Hence, m e rv = — . (2.1.1) Also equating the centrifugal force to the attractive force be-tween electron and nucleus, m e v 2 w* (2L2) where e is the charge on an electron and e 0 is the permittivity of free space ( = 3 6 ^ I O -» F / m ) -If v is eliminated between eqns. (2.1.1) and (2.1.2), n 2 h 2 e 0 7ie z m e This equation enables the radii of possible orbits to be deter-mined. Putting n — 1 and substituting for h, s 0 , n, and m, gives r = 0-529 A. This is the radius of the stable orbit nearest the nucleus and is the one normally occupied. Putting n = 2 gives a value for r of 2-11 A, and is the radius of the second possible orbit.
eBook - PDF- Jowaheer Consulting and Technologies R Van Heerden(Author)
- 2013(Publication Date)
- Macmillan(Publisher)
25 Module 2: Concepts of atomic theory Module 2: Concepts of atomic theory Overview Atomic theory is the theory of the nature of matter. This theory states that matter is made up of discrete units called atoms . The ancient Greeks first came up with the idea of the atom as far back as the 5th century BC. The Greek philosophers Leucippus and Democritus were the first to suggest that matter is made up of tiny particles that cannot be split into smaller pieces. The word ‘atom’ comes from the Greek word ‘atomos’ which means ‘indivisible’ or ‘cannot be cut’. At the end of this module, you should be able to: • Unit 2.1: Show the distribution of electrons in different orbits or shells of an atom. [ Range: silicon, germanium, gallium and arsenic .] • Unit 2.1: Describe the following terms with respect to atomic theory: valence electrons, ionised atoms, free electrons and hole. • Unit 2.1: Explain energy levels and energy bands. [ Range: insulator, semiconductor and conductor. ] • Unit 2.1: Identify the types of bonds in solids. [ Range: ionic, covalent and metallic bond. ] • Unit 2.1: Distinguish between donor and acceptor doping. • Unit 2.1: Explain the effect of heat on a conductor and semiconductor. Units in this module Unit 2.1: Basic atomic theory Unit 2.1: Basic atomic theory Overview All matter is made up of tiny units or particles called atoms. Elements such as gold, copper and carbon are made up of atoms. The atom is the smallest part of an element that can exist and still have the properties of the element. The atom An atom consists of three fundamental particles, namely electrons, protons and neutrons. The centre of an atom is called the nucleus and it consists of protons and neutrons. Protons are particles with a positive electrical charge. Neutrons are electrically neutral, that is, they have no electric charge. Electrons are particles with a negative charge that move around the nucleus.
eBook - PDF- Stephen Thornton, Andrew Rex, Carol Hood, , Stephen Thornton, Stephen Thornton, Andrew Rex, Carol Hood(Authors)
- 2020(Publication Date)
- Cengage Learning EMEA(Publisher)
You will see how it is possible to understand the behavior of semiconductors by using the quantum theory of solids. We in- tend to present just enough of the theory in descriptive fashion to allow you to appreciate the versatility and importance of semiconductor materials. 11.1 Band Theory of Solids In Chapter 10 you learned about structural, thermal, and magnetic properties of solids. Here we concentrate on electrical conduction. There are three categories of solids, based on their conducting properties: conductors, semiconductors, and insulators. As seen in Table 11.1, the electrical conductivity at room temperature is quite different for each of these three kinds of solids. Semiconductor Theory and Devices 11 Copyright 2021 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 398 Chapter 11 Semiconductor Theory and Devices Metals and alloys have the highest conductivities, followed by semiconductors, and then insulators. We have already modeled the electrical conductivity of or- dinary metals in Section 9.6. The free-electron model used in Chapter 9 does not apply to semiconduc- tors and insulators. In fact there is a different conduction mechanism for semi- conductors than for metals. Striking evidence of this fact is seen in the resistivity- versus-temperature graphs presented in Figure 11.1. Although the free-Electron Theory correctly predicts a linear increase in resistivity with temperature, semi- conductors generally exhibit decreasing resistivity with increasing temperature.
eBook - PDFElectron and Ion Microscopy and Microanalysis
Principles and Applications, Second Edition,
- Lawrence E Murr(Author)
- 2018(Publication Date)
- CRC Press(Publisher)
FUNDAMENTAL PROPERTIES OF ELECTRONS AND IONS 1 1.1 INTRODUCTION In a book proposing to deal with emission or production, operations on, and detection of electrons and ions in one form or another, it would seem desi rable at the outset to outline their intrinsic physical properties (and their associated historical development). In addition, it would also seem necessary to deal with the properties of electrons in atoms and solids, and then to describe the production and properties of ions. Indeed, the elec tron is a remarkable concept; at the risk of sounding melodramatic, it might be said that the electron represents the single most important entity in the universe. There are two very important intrinsic features associated with elec trons, namely, the fact that they are, ideally, negatively charged parti cles possessing a finite mass; and that an electron, or a beam of elec trons, possesses a wave nature akin to that normally associated with light, x-rays, or related electromagnetic radiations.* It is this wave-particle *In 1932 C. D. Anderson announced the observation of positively charged particles possessing a charge and mass identical to the negative electron. These have since come to be called positrons . 1 2 Chapter 1 dualism that renders the electron especially suited to investigating the structure and composition of matter in an electron optical device. The controversy over the wave-particle identity of electrons (cathode rays) reached its peak at the close of the nineteenth century and continued into the first two decades of the twentieth century. The resolution of the apparent wave-particle paradox was essentially found in quantum mechanics perhaps most notably in the form of Schrodinger's equation, the de Broglie matter wave concept, the Heisenberg uncertainty principle, and related contributions during the two decades after 1910.
eBook - PDFHalf-Hours with Great Scientists
The Story of Physics
- Charles G. Fraser(Author)
- 2019(Publication Date)
- University of Toronto Press(Publisher)
CHAPTER TWENTY-FOUR The Electron Theory T HE seventh epoch in the story of electricity is characterized by the electron hypothesis and its applications. The advent of this epoch was brought about by the work of so many able investigators that it is not easy to single out one man and accord him the laurels. If there is one name, however, that stands above all others, it is prob-ably that of the gifted physicist and mathematician, Sir J. J. Thomson, who became Maxwell's successor as Director of the Cavendish Labor-atory at Cambridge. A paper of his, published in 1896, proposed the assumption that atoms are composed of smaller particles—now called electrons, protons, neutrons, etc. Only a man with courage, much prestige, and irrefutable experimental data could have dared to stand up and tell the scientists of that day that what they called atoms (literally, not divisible) should really be called toms. Many of those scientists were such fanatical subscribers to the atomic theory that they resented an attack upon it as violently as they would have an attempt to undermine their religious faith—just like the peripatetics in Galileo's day. Science will have made an important advance when the fanatical support of any hypothesis is frowned out of court. Professor Jean Perrin of Paris, a friend of Pierre and Marie Curie, had shown, by using a pierced anode, that cathode rays carry negative charges. By modifying Perrin's apparatus Thomson succeeded in making an ingenious series of measurements and calculations, and his conclusions from these brought the Electron Theory into the world— and a new and marvellous epoch into not only electricity but also some other sciences: The apparatus used is represented in fig. [333]. The rays from the cathode C pass through a slit in the anode A, which is a metal plug . . . connected with the earth; after passing through a second slit B, .
eBook - PDF- J.R. Nielsen(Author)
- 2013(Publication Date)
- North Holland(Publisher)
ELECTRON T H E O R Y OF M E T A L S assumes a rather simple character, and the desired expressions for the transfer of electricity and energy will depend linearly upon the external forces, the variations in temperature, etc. These results, deduced directly from the very nature of the picture on which the Electron Theory is based, correspond exactly to what is found experimentally. Thus, as accurately as can be measured, the electric current is found to be proportional to the electric field over the very wide range of the experiments performed’. Proceeding now to detailed calculations, we shall consider two different cases; first, the simpler case in which the free electrons during the greater part, by far, of their motion are unaffected by appreciable forces from the atoms of the metal or from other electrons, so that the whole interaction between the electrons and the atoms, and among the electrons mutually, takes place in distinct, separate collisions. Next, we shall consider the more complicated case in which the electrons, during a large part of their motion, are assumed to be acted on by strong forces from the atoms of the metal. $ 2 Derivation of Equations for the Collective Motion of the Electrons in the Case in which Separate Collisions are Assumed to Occur We shall assume that the linear dimensions of the regions inside which the electrons and the metal atoms interact appreciably, i.e., the regions where collisions are said to be taking place, are very small compared to the average distance travelled by ihe electrons between collisions. For the present, we shall not make any special assumptions about the forces between the atoms and the electrons; we shall only assume that the properties of the individual metal atoms are the same in all directions, and that this symmetry exists at every point in the metal, also in the presence of external forces and when the temperature is not uniform.
eBook - PDFConcepts In Solids: Lectures On The Theory Of Solids
Lectures on the Theory of Solids
- Philip W Anderson(Author)
- 1997(Publication Date)
- World Scientific(Publisher)
2 ON E-Electron Theory A. HARTREE-FOCK THEORY 1. General Philosophy of Hartree-Fock Naturally the starting point and the basis for the one-Electron Theory are the Hartree-Fock equations, which play an absolutely fundamental role in solid-state physics. On Hartree-Fock theory good sources are Seitz' chapter and appendix, and Reitz' article in the Seitzschrift (11). One may get the impression that modern many-body theory, of which one hears so much, goes far beyond Hartree-Fock, and that therefore we should not bother with such old-fashioned stuff. This is not at all true-in fact, modern many-body theory has mostly just served to show us how, where, and when to use Hartree- Fock theory and how flexible and useful a technique it can be. For instance, Cohen and Ehrenreich (121, among others, have related plasma and correlation energy to Hartree-Fock; Valatin, Thouless (13), and others have studied nuclear collective motion by a time- dependent Hartree- Fock theory; and even the theory of superconductivity can be brought into a form almost identical with Hartree- Fock (14). In magnetism, the biggest and most im- portant recent developments are the achievements of the unrestricted Hartree- Fock method (15). lowest eigenstate *(ri . . . rn) of a system of interacting electrons having a hamiltonian The basic idea of the Hartree-Fock equations is this: One wishes to find the where V(rj) is an external potential of some sort - the potential of the nucleus in an atomic problem, of the atom cores, usually, in a solid-state problem, etc. 9 10 CONCEPTS I N SOLIDS It is difficult, however, to solve problems involving more than one electron in an external potential-even He and H2. the two simplest many-electron problems, are susceptible only to a rather lengthy numerical analysis which shows no capa- bility at all of generalization to more complicated systems. The first thing one hopes to do, then, is to find some way of treating one electron at a time.
Index pages curate the most relevant extracts from our library of academic textbooks. They’ve been created using an in-house natural language model (NLM), each adding context and meaning to key research topics.
