How does ionization potential depends on atomic size nuclear charge and electronic configuration.

How does ionization potential depends on atomic size ?

The larger the atomic size, the smaller is the ionization potential.This is due to the fact that , with increasing ionization potential, the outer electrons lie farther away from the nucleus.

Hence, the attractive pull of the nucleus on the outer electrons decreases and it becomes easier to knock out an electron from the outer shell of the atom.

The atomic size decreases from left to write along a period.Hence,ionization potential increases. The size of atom in second period elements from Li to F are as follows,

3D structure of atom from lithium to fluorine along second period. 

The change of ionization potential along  second period elements from left to right and along group VIIB elements  from top to bottom are as follow,

Why the ionization potential of potassium( K) is less than lithium( Li) ?

The ionization potential depends on the size of the atom. The larger the atomic size, the smaller is the ionization potential. Now, the size of ‘Li’ atom is much smaller than ‘K’ atom . 

Generally the outer electrons of ‘K’ atom lie farther away from the nucleus with respect to ‘Li’ atom .

Hence, the attractive pull of the nucleus on the outer electrons decreases for ‘K’ atom and it becomes easier to knock out an electron from the outer shell of ‘K’ atom. Consequently, the ionization potential of potassium ( K) is less than  that of lithium(Li).

Foe example, the ionization potential of lithium (Li) is 520 Kj / mol  but the ionization potential of potassium (K) is 418 kJ /mol .

 How does ionization potential depends on  nuclear charge? 

The force of attraction between the nucleus and the outermost electrons increases with increase in nuclear charge.

Thus , with increasing nuclear charge the amount of energy is required to pull out an electron from the outermost shell will be increases. Hence, ionization potential  increases with increase in nuclear charge.

Why the ionization potential  of sodium( Na) is less than magnesium( Mg) ? 

The ionization potential depends on nuclear charge of the atom. Now, the nuclear charge of Mg  is greater than Na .

So, the force attraction between the nucleus and the outermost electrons is higher than that of Na and hence, the energy needed to pull out an electron from the outermost shell  of  magnesium  is greater than that of Na.

Consequently, the ionization potential of sodium( Na) is less than magnesium( Mg).

How does electronic configuration of elements affect  the  ionization potential?

Certain electronic configurations  are more stable than others. For example, if an atom has fully filled or exactly half-filled orbitals, its ionization potential is higher than expected normally from its position in the periodic  table.

This is due to the fact that fully filled or exactly half filled electronic configuration of atoms  with minimum energy, are more stable than the others electronic configurations.

For example ,nitrogen and phosphorus  exhibit more stable electronic configuration with exactly half filled P-orbitals.

Why the ionization potential of oxygen is less than nitrogen?

Generally, with increasing electronegativity of atom , ionization potential increases. Since , the oxygen atom is more electronegative than nitrogen atom ,hence the ionization potential of oxygen should be greater than nitrogen.

But actually the order is reversed. Because, the nitrogen atom has exactly half filled p-orbitals , which is exceptionally more stable . Whereas , oxygen  with  p4 system has no such type of stable electronic configuration. 

  
Hence, the energy needed to pull out an electron from the outermost shell  of  nitrogen atom  is greater than that of oxygen atom. Consequently, Why the ionization potential of oxygen is less than nitrogen.

Summary

• How does ionization potential depends on atomic size and nuclear charge ? 
• Why ionization potential of oxygen is less than nitrogen ?

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