Question

The first ionisation energy of carbon atom is greater than that of boron whereas the reverse is true for the second ionisation energy. Explain.

Answer 1

"Amount of energy require to "removal of electron" from an "isolated gaseous" atom is called "ionization energy".

The "electronic configuration" of $C: { 1s }^{ 2 }{ 2s }^{ 2 }{ 2p }^{ 2 }$

The "electronic configuration" of $B: { 1s }^{ 2 }{ 2s }^{ 2 }{ 2p }^{ 1 }$

In a period when going to left to right, the "atomic size" of the atom "decreases".

Due to the smaller size of carbon compared to the boron, carbon have high ionization energy.

Small size of the carbon leads to the high nuclear power of attraction on the outer shell electrons. Therefore, high "amount of energy" required to removal of an electron.

Hence, the "first ionization energy" of carbon is higher than the boron.

After removal of an electron the electronic configuration elements is as follows.

The "electronic configuration" of ${ C }^{ + }: { 1s }^{ 2 }{ 2s }^{ 2 }{ 2p }^{ 1 }$

The "electronic configuration" of ${ B }^{ + }: { 1s }^{ 2 }{ 2s }^{ 2 }$

The electron is to be easily removed from partially filled p- orbital of carbon atom than completely filled s- orbital of boron atom.

Therefore, "second ionization energy" of "boron" is "higher than" the "carbon"."

Answer 2

Answer:

The first ionisation enthalpy of carbon is more than that of boron because the effective nuclear charge of carbon is more and its atomic size is smaller as compared to boron. ... As a result more energy is required to remove an electron from B+ than from C+.