Understanding Electronic Conductance in Metals

Electrical conductance is a measure of how easily electric current flows through a material. In metals, this conductance is primarily due to the movement of free electrons, which is why it is called electronic conductance. Metals have a large number of valence electrons that are not tightly bound to individual atoms and can move relatively freely throughout the material. These mobile electrons are responsible for carrying the electric charge when a voltage is applied.

How Temperature Affects Electronic Conductance in Metals

The electronic conductance of a metal is significantly affected by temperature. Let's explore this relationship:

• In a metal, atoms are arranged in a regular lattice structure.
• The free electrons move through this lattice.
• At any given temperature above absolute zero, the metal atoms vibrate about their fixed positions in the lattice.
• These vibrations are not static; they increase in amplitude as the temperature rises.
• The free electrons, as they move through the metal, collide with these vibrating atoms (or more accurately, the thermal vibrations of the lattice).
• More frequent or more vigorous collisions impede the flow of electrons.
• Higher temperature means increased thermal vibrations of the lattice atoms.
• Increased vibrations lead to more frequent scattering of the free electrons.
• This increased scattering makes it harder for electrons to move through the metal, effectively increasing the resistance to current flow.

Since resistance is the inverse of conductance, an increase in resistance means a decrease in conductance. Therefore, as the temperature of a metal increases, its electronic conductance decreases.

Let's summarize the relationship:

Based on this understanding, the electronic conductance through metals decreases with increase in temperature because the increased thermal vibrations of the lattice atoms impede the flow of electrons more effectively.

Revision Table: Electronic Conductance and Temperature

Additional Information on Electrical Conductivity

While metals show a decrease in electronic conductance (and thus conductivity) with increasing temperature, other materials like semiconductors behave differently. The conductivity of semiconductors typically increases with increasing temperature because the thermal energy helps to free up more charge carriers (electrons and holes), even though scattering also increases.

The relationship between resistivity ($\rho$), resistance ($R$), conductivity ($\sigma$), and conductance ($G$) for a material of length $L$ and cross-sectional area $A$ is:

• $R = \rho \frac{L}{A}$
• $G = \frac{1}{R}$
• $\sigma = \frac{1}{\rho}$
• $G = \sigma \frac{A}{L}$

So, conductance is directly proportional to conductivity for a given geometry. When electronic conductance decreases, it means the electronic conductivity also decreases.