Question

Explain the electrical, optical, magnetic and thermal properties of METALS based on the band structure, electronic configuration and atomic structure.

Answer 1

A conductor is a material which contains movable electric charges. In metallic conductors such as copper or aluminium, the movable charged particles are electrons. Positive charges may also be mobile, such as the cationic electrolyte(s) of a battery or the mobile protons of the proton conductor of a fuel cell. Insulators are non-conducting materials with few mobile charges; they carry only insignificant electric currents. In describing conductors using the concept of band theory, it is best to focus on conductors that conduct electricity using mobile electrons. According to band theory, a conductor is simply a material that has its valence band and conduction band overlapping, allowing electrons to flow through the material with minimal applied voltage.

Metals are elements that give off “free” electrons. Metals generally have anywhere between 1 to 3 electrons excess of a closed shell. metals give off electrons and become positive ions. Non-metals accept electrons and become negative ions. Hydrogen (H) and Helium (He) are two light elements which are non-metallic in nature. Hydrogen lacks one electron to complete its one and only one shell. Helium has 2 electrons in its only orbit.The metals are placed on the left side and the centre of the periodic table. The non-metals are placed on the right side of the periodic table. Hydrogen is the only non-metal that is placed on the left-hand side of the periodic table. The reason for this is that the electronic configuration of H is 1s1, same as the Group I A elements or the alkali elements such as Na, and K. The middle portion of the periodic table consists of elements that are called transition metals elements. These elements are metallic in nature but not as metallic as alkali (Na, K, Cs etc) or alkaline earth metals (Mg, Ca etc.)

Atoms are arranged like closely packed spheres. Because outer electrons of metal atoms are delocalized and highly mobile, metals have electrical and thermal conductivity. ... In general, metals are denser than nonmetals. This is due to the tightly packed crystal lattice of the metallic structure.

The optical properties of metals are a bit more complicated than that of insulators. Since metals are very conductive, photons (which are electromagnetic) excite the electrons, which then re-emit light. This re-emission (or reflection) of light is why metals look shiny. Noble metals (gold, silver, platinum) look particularly shiny because their surfaces do not form insulating oxides when exposed to air, which many metals (such as sodium) do within seconds.

Metals consist partially filled high-energy conduction bands. When photons are directed at metals, their energy is used to excite electrons into unoccupied states. Thus metals are opaque to the visible light. Metals are, however, transparent to high end frequencies i.e. x-rays and γ-rays. Absorption of takes place in very thin outer layer. Thus, metallic films thinner than 0.1μm can transmit the light. The absorbed radiation is emitted from the metallic surface in the form of visible light of the same wavelength as reflected light. The reflectivity of metals is about 0.95.

The most common metals used for permanent magnets are iron, nickel, cobalt and some alloys of rare earth metals. There are two types of permanent magnets: those from “hard” magnetic materials and those from “soft” magnetic materials. “Hard” magnetic metals tend to stay magnetized over a long period.

In addition to atomic vibrations (phonons), thermal excitation of electrons can also make contribution to heat capacity.

To contribute to bulk specific heat, the valence electrons would have to receive energy from the thermal energy, ~kT. Thus, only a small

fraction of electrons which are within kT of the Fermi level makes a contribution to the heat capacity. This contribution is very small and

insignificant at room temperature.

The electron contribution to Cv is proportional to temperature

and becomes significant (for metals only) at very low temperatures.