Electrical Conductivity
Definition and meaning of Electrical Conductivity in chemistry.
Electrical conductivity is a measure of a material's ability to allow the flow of electric charge through it, expressed as the reciprocal of resistivity. Substances with high conductivity contain freely mobile charge carriers, such as delocalized electrons in metals or dissolved ions in electrolyte solutions.
In more detail
In metals, conductivity arises from a "sea" of delocalized valence electrons that move freely through the lattice under an applied electric field. In ionic compounds, conductivity requires mobile ions, which is why solid ionic crystals do not conduct but molten salts and aqueous ionic solutions do, since the ions can then migrate toward oppositely charged electrodes. Electrolyte solutions are classified as strong, weak, or nonelectrolytes based on how fully they dissociate into ions, which directly affects how well they conduct. Conductivity measurements are widely used to assess water purity, monitor titrations, and determine ion concentrations in solution.
Key facts
| SI Unit | Siemens per meter (S/m) |
|---|---|
| Reciprocal of | Resistivity (rho) |
| Field | Physical Chemistry |
| Key carriers | Delocalized electrons (metals) or mobile ions (electrolytes) |
A solution of sodium chloride (NaCl) in water conducts electricity because NaCl fully dissociates into mobile Na+ and Cl- ions, whereas pure distilled water conducts only very weakly since it contains few free ions.
Frequently asked questions
Why does solid NaCl not conduct electricity but molten NaCl does?
In the solid, Na+ and Cl- ions are locked in a fixed crystal lattice and cannot move. When melted, the lattice breaks down and the ions become mobile, allowing them to carry charge.
What is the difference between conductivity and molar conductivity?
Conductivity describes a solution's overall ability to carry current, while molar conductivity normalizes this value per mole of dissolved electrolyte, allowing comparison between solutions of different concentrations.