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Why is the first ionisation energy of oxygen less than that of nitrogen? A - CIE - A-Level Chemistry - Question 7 - 2021 - Paper 1
Question 7
Why is the first ionisation energy of oxygen less than that of nitrogen? A. The nitrogen atom has its outer electron in a different subshell. B. The nuclear charge o... show full transcript
Worked Solution & Example Answer:Why is the first ionisation energy of oxygen less than that of nitrogen? A - CIE - A-Level Chemistry - Question 7 - 2021 - Paper 1
Step 1
C. The oxygen atom has a pair of electrons in one p orbital that repel one another.
Answer
The first ionisation energy is the energy required to remove the outermost electron from an atom. In this case, for oxygen, the electron configuration is generally described as 1s² 2s² 2p⁴. This means that within the 2p subshell, there are paired electrons. When electrons are paired in the same orbital, they experience electron-electron repulsion. This repulsion makes it easier for the outer electron to be removed compared to nitrogen, which has a configuration of 1s² 2s² 2p³, where all its p electrons are unpaired. As a result, oxygen has a lower ionisation energy due to this repulsion among the paired electrons.