Classification of Substances on the basis of Conductivity Chemistry Notes
→ Conductors: The substances in which flow of electric current is possible, are called conductors. Examples: Cu, Ag, Sn and other metals etc. Types of Conductors-These are of following types:
→ Metallic Conductors-Those metallic substances in which electric current flows without any chemical change are called metallic conductors. Examples: Cu, Ag etc.
→ The flow of electric current is due to electrons. Electric current flows in opposite direction to the flow of electrons. The conductivity of metallic conductors depends on the following factors:
- Number of valence electrons per atom in metal.
- Structure and nature of metal.
- Density of metal.
- Temperature (metallic conductivity decreases with increase in temperature).
→ In metallic conductors, electrons enter from one end and exit from other end. Some non-metals like-graphite, carbon black, organic polymers etc., also represent this type of conductivity.
→ Electrolytes – Those substances, in which the flow of electric current is possible in molten state or in aqueous solution, are called electrolytes. These substances decompose in molten state or in aqueous solution as a result, ions are formed. Electric current flows due to these ions. This type of conductors is called electrolytic conductors.
→ These substances are non-conductors in solid state because ions are not free to move. For example : Solid NaCl is an insulator while the aqueous solution of NaCl is conductor of electricity.
→ Insulators-These substances do not conduct electricity. Examples: Glass, Clay, Plastic etc.
→ Semi-conductors-Those substances whose conductivity lies in between conductors and insulators, are called semi-conductors. Examples : Silicon (Si). Doped Silicon, Gallium arsenide etc.
→ Super Conductors-Those substances which have zero resistance or infinite conductivity, are called super conductors. Some metals and alloys are super conductors at very low temperature i.e., 0-15 K. Many ceramic substance and mixed oxides show super conductivity at high temperature i.e. 150 K.
Factors Affecting Electronic or Metallic Conductivity :
Conductivity depends up on the following factors:
- Structure and Nature of Metals – The metals which have more number of unpaired electrons, also possess high conductivity.
- Number of Valence Electrons per Atom – Those atoms which have more number of valence electrons, also possess high conductivity.
- Temperature -The conductivity of metals decreases with increase in temperature because the energy of electrons increases with increase in temperature by which they vibrate to and fro. As a result, they collide with each other and conductivity decreases.
→ Electrolytes and Their Classification Those substances which conduct electricity in molten state or in aqueous solution, are called electrolytes. Electrolytes can be classified as follows:
→ Strong Electrolytes-Those electrolytes which are dissociated completely into ions in solution, are called strong electrolytes. These include salts made up of strong acid strong base, strong acid-weak base and weak acid-strong base. Examples : NaCl, KCl, HCl, KNO3 CH3COONa, NH4Cl etc.
→ Weak Electrolytes-Those electrolytes which are not dissociated or ionized completely in solution, are called weak electrolytes. These include salts of weak acid and weak base. Examples : CH3COOH, NH4OH, HCN, ZnCl2 H3BO3.CH3CH2COOH etc.
→ Since these are not dissociated completely so an equilibrium is established between weak electrolyte and ions produced in solution. So, the quantity of ionization of weak electrolyte is called degree of dissociation or degree of ionization.
Factors Affecting the Conductivity of Electrolytic Solution :
→ Temperature – The conductivity of electrolytic solutions increases with increase in temperature because the degree of ionization increases and the movement of ions also increases.
→ Nature of Solvent and Viscosity – The viscosity of solvent depends on solvent-solvent interactions. The viscosity of solvent also increases on increasing interactions. So, the movement of ions decreases on increasing viscosity due to which their conductivity also decreases.
→ Solvation of lons – The solvation of ions depends on ions of solute and interactions between molecules of solvent. These are called solute solvent interactions. If solute-solvent interactions are strong then ions of solute are highly solvated and their electric conductivity will be low.
→ Interionic Attraction – The attraction between ions of solute molecules or electrolytes and solvent molecules is called inter-ionic attraction. The energy produced in ion-solvent interaction is called “solvation energy and if water is used as solvent then it is called “hydration energy”. Hence, if the amount of ion-ion attraction energy is more than ion-solvent attraction then electrolyte does not dissociate. These types of electrolytes are taken in class of weak electrolytes and hence as solvation energy increases, conducting also increase.
→ Dilution-The dilution for both types of electrolytes i.e, strong and weak increases the electric conductivity, It decreases attraction between ions. As a result, the conductivity of ions increases.
→ Concentration of Solution-Greater the concentration of electrolytic solution, lesser is its conductivity. The degree of dissociation increases with dilution. Due to which the conductivity of solution increases.
Differences between Metallic Conductor and Electrolytic Conductor :
|This type of conductivity is due to movement of electrons.||This type of conductivity is due to movement of ions.|
|There is no change in chemical properties of conductor.||Dissociation of electrolyte takes place i. e., it undergoes chemical change.|
|It does not involve transfer of matter.
|It involves transfer of matter in the form of ions.|
|Electronic conductivity decreases with increase in temperature.||Electrolytic conductivity increases with increase in temperature.|
|The conductivity of metallic conductors is generally high.||The conductivity of electrolytic solutions is generally low.|