Properties of Solids - Electrical Properties

Properties of solids have been exploited for various new innovations in electronic and magnetic devices like transistors, computers, telephones etc.
Properties of the solids mainly depend upon their structure and composition. Three main properties are discussed below.

Electrical properties

Electrical conductivity varies from 10⁸ Ohm cm^-1 in metals to 10^-12 ohm^-1cm^-1 in insulators. Based on their conductivity solids can be divided into three categories.
(a) Conductors (b) Semiconductors (c) Insulators.

Conductors

Solids through which electricity can flow to a large extent are called conductors.
Depending upon the type of charge carriers, the conductors are further classified as metallic and electrolytic conductors. In metallic conductors, electrons are the charge carriers. In electrolytic conductors, ions are the charge carriers. Therefore electrolytic conductors conduct only when there are mobile ions i.e., in molten state. However in solid state they conduct electricity only to a small extent, which is due to the presence of defects (holes, electrons etc) Examples: NaCl, KCl as electrolytic and metals as metallic.

Insulator

The solids, which almost do not allow the electricity to pass through them are called insulators. Examples: S, P, plastics, wood etc.

Semiconductors

The solids whose conductivity lies between metallic conductors and insulators are called semiconductors. The electrical conductivity of semiconductors is due to the presence of impurities and defects. Their conductivity increases with increase in temperature as the defects increase with the increase in temperature. The magnitude of the electrical conductivity strongly depends on the number of electrons available to participate in the conductor process.
In metals the atomic orbitals from molecular orbitals, which are so close in energy to each other as to form a band. If conduction band is not completely full or it lies very close to a higher unoccupied band, then electrons can flow easily under an electric field thereby showing conductivity. In case of semiconductors, the gap between valence band and the conduction band is small and hence some of the electrons may jump from valence band to conduction band and result is some conductivity.
In case of insulators, the difference of energy between valence band and conduction band so large that electron transition, doesn't take place. Hence, no conductivity is shown.

fig 2.36 Transition metal monoxides all have NaCl structure and show marked difference in electric properties. Some are metallic while others are semi conductors or insulators.
It is interesting to mention that ReO₃ is like metallic copper in its conductivity and appearance.

Hernandez Caballero Indiana M. CI: 15.242.745
Asignacion: EES
Fuente: http://www.tutorvista.com/content/chemistry/chemistry-iv/solid-state/electrical-properties.php

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