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Conductors

Any substance which allows the electric current to pass through it, is called an electrical conductor. The substance can be solid metallic in nature or can be in fused state as well but the flow of energy in form of electrical charge takes place only when there is less resistance to the flow of this charge. The lesser the resistance the higher the flow electrical charge through a solid body and more the number of free ions in fused state, easier the flow of charge in it.

 

What is a Conductor?

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Definition:
A conductor is a material which permits the flow of energy. A material which allows the flow of charged particles is an electrical conductor. A material which allows the transfer of thermal energy is a thermal conductor or heat conductor.

Conductors of electricity:

Electrical conductors are materials which contain movable electric charge. The charge may be positive or negative. In case of metallic conductors like copper or aluminum the movable charge particles are electrons and in electrolytic conduction the movable charge particles are ions, either positive ions or negative ions.

There are two types of conductors:
  1. Metallic conductors
  2. Electrolytic conductors

Metallic conductors:

Metallic conductors are those which allow electricity to pass through them without undergoing any chemical change. For example, copper, silver etc. In metallic conductors, the conduction occurs due to the movement of electrons under the influence of applied electrical potential. The stream of electrons constitutes the current.

Electrolytic conductors:

Electrolytic conductors are those which allow electricity to pass through them by undergoing a chemical change. The conduction in ionic solids is due to the migration of ions or other charged particles under the applied field. Due to strong electrostatic forces of attraction between the oppositely charged ions, they do not conduct electricity in the solid state. However, they conduct electricity to a good extent when they are in the molten state or in the form of their aqueous solutions. In theses states, the ions of the electrolytes become free and they conduct electricity due to the free movement of ions. In the solid state, some ionic solids with defects may conduct electricity to a small extent because the migration becomes possible due to the presence of vacancies or interstitial sites.

Electrical Conduction in Metals

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The conduction in most of the solids occurs through electron movement under an electric field. Therefore, in the solids where the conduction is by the movement of electrons, the electrical conductivity depends on the number of electrons available to participate in the conduction process. In metals, the conductivity strongly depends on the number of valence electrons available per atom. The difference in electrical conductance behavior of conductors, insulators and semiconductors can be explained with the help of the band model. It is based on the molecular orbital theory.

Band Model:


The basis of the band model is that a metal lattice has an extremely large number of atoms. The atomic orbital of metal atoms form a large number of molecular orbital which are so close in energy to each other that they form a band. If the band is partially filled or it overlaps with a higher energy unoccupied band, then electrons can easily flow under an applied electric field and the metal shows conductivity. In general, the electrical conduction of solids depends upon the energy gap between the filled valence band and next higher vacant energy band.
The outermost filled energy band is called Valence Band and the next empty band in which electrons can move is called Conduction Band.
The spaces between the valence band and the conduction band represent energies forbidden to electrons and are called Energy Gaps or Forbidden Zone.
  • In metals, the conduction band is close to the valence band and, therefore, the electrons can easily go into the conduction band. Therefore, metals are good conductors.
  • In insulators, the energy gap between valence band and conduction band is very large. Therefore, the empty bands are not accessible for conduction and therefore, electrons from the valence band cannot move into the conduction band.
  • Several solids have properties intermediate between metals and insulators. These are called semi-metals or semi-conductors.
They have only a small difference in energy between the filled valence band and empty conduction band. If the crystals were cooled to absolute zero, the conduction band would be empty and the electrons occupy their lowest possible energy levels. The material would be a perfect insulator. However, at ordinary temperatures, some electrons are thermally excited from the valence band to the conduction band and hence they can conduct electricity by the passage of electrons at normal temperature. The conductivity is in between that of a metal and an insulator and depends upon the number of electrons in the conduction band.


List of Conductors

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  • silver
  • copper
  • gold
  • aluminum
  • iron
  • steel
  • brass
  • bronze
  • mercury
  • graphite
  • dirty water
  • concrete

Examples of Conductors

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Metallic Conductors:


Metallic conductors are those which allow the electricity to pass through them without undergoing any chemical change. For example, copper, silver etc. In metallic conductors, the conduction is due to the movement of electrons under the influence of applied electrical potential. The stream of electrons constitutes the current.

Electrolytic Conductors:


Substances that allow the passage of electricity through their molten state or aqueous solutions and undergo chemical decomposition.

Difference between Metallic and Electrolytic Conduction: 

Metallic Conduction Electrolytic Conduction
Passage of Charge by electrons. Passage of charge by ions in molten and aqueous state.
Passage of charge brings about only physical changes. Does not involve transfer of matter. Brings about physical and chemical changes. Involves transfer of matter in the form of ions.
Resistance increases with temperature because of obstacles of vibrating kernels. Resistance decreases with temperature because viscosity decreases.
Conducting power is high. Conducting power is low.

Is Conductivity a Chemical Property?

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Solved Examples

Question 1: What are the factors, on which electronic conductance depend?
Solution:
Electronic or metallic conductance depends on following factors

1. the nature and structure of the metal 
2. the number of valence electrons per atom
3. the density of metal 
4. temperature (it decreases with increase in temperature)



Question 2: Define conductance and its SI unit
Solution:
It is a measure of the ease with which current flows through a conductor. It is expressed as G and numerically it is equal to the reciprocal of resistance, i.e. 

G = $\frac{1}{R}$

SI unit of conductance is Ohm-1 or siemens . 



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