Expressions obtained will be useful when considering real conductors i free electrons. Unit1 classical free electron theory physics youtube. Postulates of classical free electron theory 1 the free electrons of a metal are having like the moleculesof a gas in acontainer. According to this theory, the metals containing the free electrons obey the laws of classical mechanics.
The classical free electron theory of metals drude lorentz theory of metals. This approximation starts with the notion that the metal contains a collection of ion cores, each core consisting of a nucleus and shells of tightly bound electrons, and a number of electrons that are not bound to any particular nucleus. The free electron model considers that metals are composed of a quantum electron gas where ions. According to this theory, a metal consists of electrons which are free to move about in the crystal like molecules of a gas in a container. The valence electrons of metallic atoms are free to move in the spaces between ions from one place to another place within the metallic specimen similar to gaseous molecules so that these electrons are called free electron gas.
Our consideration will be based on a semiclassical model. For the love of physics walter lewin may 16, 2011 duration. Sommerfelds free electron theory of metals physics assignment. Electron dynamics and fermi surfaces electron dynamics the next important subject we address is electron dynamics in metals. One of the earliest successful approximations in the theory of metals was the free electron theory.
The classical free electron theory is based on the following postulates. This idea was given by drude and he utilized it to explain many properties of metals satisfactorily such as electrical conductivity, thermal conductivity etc. The term semiclassical comes from the fact that within this. Such freely moving electrons cause electrical conduction under an applied field and hence referred to as conduction electrons. B m s institute of technology classical free electron theory. The distribution of electrons in various allowed energy levels occur as per pauli exclusion principle. Quantum free electron theory of metals science key.
The treatment of a metal as containing a gas of electrons completely free to move within it. About that time, geometrical terms such as extremal sections, curvatures, diameters, limiting points began to appear in papers on the electron theory of metals. It could not explain the negative temperature coefficient of resistivity for certain solids 2. The free electron model solved many of the inconsistencies related to the drude model and gave insight into several other properties of metals. Quantum free electron theory was proposed by arnold sommerfeld. Engineering physics ii unit 1 conducting materials notes topic covered. Pdf free electron theory 201516 vtu shashank mohan. From the instant of sudden disappearance of an electric field across a metal, the average velocity of the conduction electrons decays. Drude in 1900 and developed by lorentz in 1909 to explain electrical conduction in metals. Freeelectron theory of metals accessscience from mcgraw. Srit unit iii free electron theory engineering physics. Freeelectron theory of metals article about freeelectron. In solidstate physics, the free electron model is a simple model for the behaviour of charge carriers in a metallic solid. Free electron model of metals, in solidstate physics, representation of a metallic solid as a container filled with a gas composed of free electrons i.
Some appreciation of the term of relaxation time dt. According to the classical free electron theory the value of specific heat of metals is given by 4. Ravindran, phy075 condensed matter physics, spring 20 16 july. Thermal properties of the free electron gas 1 groundstate properties of the electron gas 2 the fermidirac distribution 3 thermal properties of the free electron gas 4 the sommerfeld theory of conduction in metals daniele to oli january 11, 2017 27 48. The simplest metals are the alkali metals lithium, sodium, potassium, na, cesium, and rubidium. The valence electrons of the constituent atoms become conduction electrons and move about freely through the volume of the metal. Conductivity, hall effect and other transport phenomena will be treated separately in chapter 11. The free electron theory of metals using classical laws was developed by dude and lorentz in the beginning of last century. Conductors classical free electron theory of metals electrical and thermal conductivity wiedemann franz law lorentz number draw backs of classical theory quantum theory fermi distribution function effect of temperature on fermi. Metals drudes classical theory theory by paul drude in 1900, only three years after the electron was discovered. Mar, 2017 start free trial sign in engineering physics by s. May 20, 2006 why did the free electron theory of metals fail the free electron of model my effort. Especially classical free electron theory and quantum free electron theory of metals.
However, the following assumptions of classical electron theory continue to be applicable in quantum free electron theory also. According to classical free electron theory of metals electrical conductivity is given by, from the above equation, relation between temperature and electrical conductivity is given by hence, classical free electron fails to explain the temperature dependence of electrical conductivity. In this chapter the free electron theory of metals as developed by sommerfeld and others will be discussed. A metal is imagined as the structure of 3dimensional array of ions in between which, there are free moving valence electrons confined to the body of the material. The classical free electron theory of metals drude lorentz theory of metals postulates. It was developed in 1927, principally by arnold sommerfeld, who combined the classical drude model. Drude treated the free electrons as a classical ideal gas but the electrons should collide with the stationary ions, not with each other. Drude theory of conduction basics of free electron theory and electrical conductivity. As per his investigation, the behavior of free electron in different possible energy states is explained, how the large number of electrons are disturbed in the energy states. It turns out that the nearly free electron approximation is quite reasonable for simplemetals withpredominant s. Classical drude theory of metals successes and limitations of the classical model. In a metal conduction electrons move almost freely. Apr 10, 20 the phenomena such a photoelectric effect, compton effect and the black body radiation couldnt be explained by classical free electron theory. The classical theory had several conspicuous successes, notably the.
What are the drawbacks of classical free electron theory. Put free electrons into a very wide potential well the. Electronic structure 103 in the following chapter, we will also learn some experimental techniques that are currently used to investigate the electronic properties of the bulk and the surface. Jun 15, 2018 neglecting the electron electron interaction and the electron ion interaction, it appears as if the electrons move in a confined box with periodic collision with ions in the lattice. Introduction to the electron theory of metals the electron theory of metals describes how electrons are responsible for the bonding of metals and subsequent physical, chemical and transport properties. This textbook gives a complete account of electron theory in both periodic and nonperiodic metallic systems.
The main assumptions of classical free electron theory are. Sommerfield model for free electron theory 11 success of quantum free electron theory according to classical theory, which follows maxwellboltzmann statistics, all the free electrons gain energy. The failure of the free electron theory of metals physics. Drude theory of conduction basics of free electron theory and electrical conductivity part 1. Mar 18, 2018 classical free electron theory of metals physics video. The valence electrons of metallic atoms are free to move about the whole volume of the metals like the molecules of a gas in a container. Electron theory definition of electron theory by the free. Later, quantum mechanics became the basis for the theory of most of the general properties of simple metals such as sodium, with one free electron per atom, magnesium with two, and aluminum with three. The classical free electron theory was introduced by p.
The collection of valence electrons from all the atoms in a given piece of metal forms electron gas. Electron theory synonyms, electron theory pronunciation, electron theory translation, english dictionary definition of electron theory. Electron theory of complex metallic alloys sciencedirect. The free electrons are treated as equivalent to gas molecules and they are. The discussions assume the readers familiarity with the material pertaining to appendixes b, c, d, and e. All metals share common properties excellent electrical conductors excellent thermal conductors shiny when polished all due to the free electrons of the metallic bond outline classical drude theory of metals successes and limitations of the classical model sommerfeld theory of metals. Nov 05, 2016 behavior of free electron is different from electron in the potential field of the crystal as current is due to flow of charge, electron behavior in external electric field is important 9.
Dm represents documents in the archives of the deutsches museum in. All due to the free electrons of the metallic bond. The valence electrons of atoms are free to move about the whole volume of the metal, like the molecules of a perfect gas in a container. So it leads to much larger predicted quantities than that is actually observed.
Assumptions we will first consider a gas of free classical electrons subject to external electric and magnetic fields. To assign the peak in the optical absorption spectrum of alkalis observed in figure 1. Atomic selectrons are delocalised due to overlap of outer orbits. It is free to move throughout the volume of the metal. The valance electrons are not affected by theeltlectronion it tiinteraction. Solid state, by providing a large and ready number of concrete prob. This paper continues an earlier study of the first phase of the development from 1926 to 1928 devoted to finding the general quantummechanical framework. Prominent examples are the alkali metals and aluminum. The valence electrons of atoms are free to move about the whole volume of the metals like the molecules of a perfect gas in a container. That time the valance electrons in metals were regarded as the noninteracting particles of an ideal gas. In solidstate physics, the free electron model is a simple model for the behaviour of.
Then sommerfelds elementary quantum mechanical theory of metals is discussed. The main assumptions of quantum free electron theory are, the energy levels of the conduction electrons are quantised. Because it was unable to answer why the mean free path of electrons reaches 20nm in a good conducting metal like silver in room tempereture. Drude model conductivity frequency dependence plasma. The free electrons, considered identical to the outermost, or valence. The free electron model considers that metals are composed of a quantum electron gas where ions play almost no role.
Classical free electron theory of metals this theory was developed by drude and lorentz and hence is also known as drudelorentz theory. The theory was originally proposed in 1900 to describe and correlate the electrical and thermal properties of metals. Free electron theory of metals nicholas research group. The development of the quantummechanical electron theory of metals. Theory of free electrons in metals elefterios lidorikis room. Engineering physics ii unit 1 conducting materials notes. Drudes theory treated the electrons as an ordinary classical gas. In an atom electrons revolue around the nucleus and a metal is composed of such atoms. According to this theory, the metals containing free electrons obey the. The development of the quantummechanical electron theory of.
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