Factors Influencing Ionisation Energy

The various factors which influence the Ionisation energy are;

¤    Size of atom

The Ionisation energy depends upon the size of atom, because with increase in size, the distance between nucleus and valence electrons increases and hence force of attraction between nucleus and valence electron decreases. As a result of which the valence electrons are loosely held and smaller energy is required to remove an electron. Thus Ionisation energy decreases with increase in size and increase with decrease in size.

¤    Nuclear charge

As the nuclear charge increases, the force of attraction between nucleus and valence electrons increases and hence it is difficult to remove an electron from valence shell. Thus with increase in nuclear charge, the Ionisation energy increases.

¤    Screening effect or Shielding effect

The inner electrons present in shells between nucleus and valence shell reduce the attraction between nucleus and the outermost electrons. This shielding effect depends upon the number of inner electrons. Larger the number of electrons in the inner shells, the greater is the screening effect. More the Shielding effect, easier will be to remove an electron and hence lesser will be ionisation energy.

¤    Penetration effect

s – electrons are closer to the nucleus than p-electrons, which is closer than d – electron and these inturn are closer than f-electrons of the same principle energy level. Hence s – electrons experience more attraction from the nucleus than p, d and f – electrons. Thus Ionisation energy to remove an electron from a given energy level decrease in order s > p > d > f.

¤    Electronic Configuration

Electronic Configuration plays vital role in determining the value of Ionisation energy. Atoms having stable configuration (i.e. fully filled or half filled) has least tendency to lose electron and hence have high value of I. E.