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The first Ionization enthalpy of nitrogen is high compared to oxygen gives reasons

The first Ionization enthalpy of nitrogen is high compared to oxygen gives reasons

Grade:11

1 Answers

Vikas TU
14149 Points
4 years ago
Dear student 
The first ionisation energy increases across a period. This is because when moving from left to right, the atomic number increases which means that the nuclear charge increases. As a result, the valence electrons are held more tightly to the nucleus and hence we expect the first ionisation energy to increase across the group.
But this trend is not followed when moving from nitrogen to oxygen. Wikipedia tells me that the first ionisation energies of nitrogen and oxygen are 1402.3 kJ mol−1 and 1313.9 kJ mol−1 respectively. Ionisation energy of nitrogen is found to be greater than oxygen. Let's see why.
Electronic configuration of Oxygen is
1s2 2s2 2p4
Electronic configuration of Nitrogen is
1s2 2s2 2p3
You must be knowing that an atom containing half filled or fully filled orbitals are very stable. Nitrogen has a half filled 2p orbital. So when it is already stable, why would it want to lose an electron upon supplying energy and become unstable? This is why one requires large amounts of energy to ionised the nitrogen atom.
On the other hand, since Oxygen is already unstable relative to Nitrogen, by losing one electron it attains a stable half filled 2p orbital. So oxygen undergoes ionisation at a relatively lower energy. This is why nitrogen has a higher ionisation energy than oxygen.

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