chemistry

IONIZATION POTENTIAL OR IONIZATION ENERGY

The minimum amount of energy required to remove the most loosely bound electron from an isolated gaseous atom is called its first ionization potential 

The energy required to remove an electron from a unipositive ion is called its second ionization potential 

The number of ionisation potentials of an atom is equal to it's atomic number. The second ionization potential is greater than the first ionization potential.

With the successive removal of electrons ionization potential increases due to increased nuclear charge.

I₁= 13.6 X z² (z = effective nuclear charge)

Ionization potential is measured in eV/atom and ionization energy is measured in kJ/mole (1 eV/atom = 96.45 kJ mole^–1or 1 eV/atom = 23.06 kcal/mole)

Ionization energies are determined from spectral studies as well as from discharge tube experiments.

Ionization potential depends on the following factors.

1)   Atomic radius.

2)   Nuclear positive charge

3)   Screening effect or shielding effect.

4)   Extent of penetration of valence electrons.

5)   Completely or half-filled sub shells.

lionization potential decreases as the atomic radius increases.

Ionization potential increases as the nuclear positive charge increases.

SCREENING EFFECT:

The protection given by the inner electrons to the valence electrons from the nucleus is called screening effect.

As the inner electrons increase in number, screening effect increases and the ionization potential decreases.

The extent of penetration of orbitals towards the nucleus follows the order s > p > d > f for a given principle quantum number n.

With increase in the extent of penetration, I.P. increases. s > p > d > f.

Atoms having completely filled and half filled orbtials are more stable and need more energy for ionization.

Be has greater ionisation potential than B due to the completely filled s-orbital.

Nitrogen has greater ionization potential than oxygen due to the half filled p-orbitals.

I₁of 2^ndperiod: Li < B < Be < C < 0 < N < F

I₂of 2^ndperiod: Be⁺ < C⁺< B⁺ < N⁺< F⁺ < 0⁺< Li⁺

TREND OF IONIZATION POTENTIAL:

Ionization potential decreases down the group due to increase in size and increases in screening effect.

lonisation potential increase in a period form left to right due to decrease in size and increase in nuclear charge.

In any given period, alkali metal has less. I.P. value and inert gas has highest I.P. value.

In transition series I.P. value slowly ↑due to less screening effect of (n – 1)d electrons. Alkali metals have low I.P values. Lowest I.P. value is for Cs.

Noble gases have high I.P values. Highest I.P. value is for He.

In transition families I.P. value ↓from 3d to 4d and slightly increases there after due to lanthanide contraction.

The I₁values of 1^st few elements: He > Ne > F > Ar > N > Kr > 0 etc.

I.P. curve is obtained by plotting I.P. Vs atomic number. In I.P. curve, peaks are occupied by Inert gases.

Troughs are occupied by alkali metals.

Ascending portions are occupied by II-A group metals.

Descending portions are occupied by VII-A group elements.