What is penetration effect ?How does penetration effect influence the ionization energy ?

What is penetration effect ?

The probability of electrons coming closer to the nucleus in their motion around the nucleus is called penetration effect.

How does penetration effect  influence the ionization  energy ? 

It has been found that the ‘S’ electrons have greater probability of coming closer to the nucleus  than the P,d or f electrons of the same principal energy shell. 

In other words, ‘S’ electrons penetrate more towards the nucleus than the ‘P’ electrons and the penetrating power of the electrons in the given principal energy shell  varies as S> P> d>f.

Thus the ‘S’ electrons experience more attraction from the nucleus than the p d or f electrons of the same principal energy shell.

Therefore, the ionization potential for pulling out an ‘s’ electron is maximum  and it decreases in pulling out a p , d or f electron of the same principal energy shell in order of their motion.

Why  the ionization energy  of beryllium( B)  is greater than boron( B) ? 

The electronic  configuration of beryllium( B) and  boron( B) atoms are as follows,

The ‘s’ electrons penetrate more towards the nucleus than the ‘P’ electrons and the penetrating power of the electrons in the given principal energy shell  varies as S> P> d>f. 

Thus the ‘S’ electrons experience more attraction from the nucleus than the p d or f electrons of the same principal energy shell.

Therefore, the ionization energy  for pulling out an ‘s’ electron is maximum  and it decreases in pulling out a p , d or f electron of the same principal energy shell in order of their motion.

For the above reason, the ionization energy of beryllium( B)  is greater than boron( B).

How  does shielding effect influence the ionization energy ?

The electrons in the inner shells act as a screen or shield between the nucleus and the electrons in the outer most shell. 

This is known as screening effect. The larger the number of electrons in the inner shells, the greater is the screening effect.

Consequently, the electrons in the valency shell experience less attraction from the nucleus. Hence, the ionization energy would be low.

Why ionization energy of copper (Cu) is greater than potassium(K) ?

In case of copper atom, inner d-orbital has less shielding effect with respect to the inner p-orbital of potassium atom.

 Hence the attraction force of nucleus  towards  outer most 4s electron  for copper atom  is greater than potassium atom.

Consequently, the ionization  potential of   of copper (Cu) is greater than potassium(K).

Practice problem:

What is shielding effect?How it affect the ionization potential ? 

Why the ionization of Na is less than Al ?

What is penetration effect ? why I.P of Be is greater than B ? 

Click here: Ionization energy and also screening effect.