Question

problem: first ionization energy describes the amount of energy needed to remove the first electron from an atom. second ionization energy describes the amount of energy needed to remove the second electron from an atom once the first is removed, and so on. sodium’s (na’s) first ionization energy is 495.8 kj/mol. its second ionization energy is 4562 kj/mol, and its third ionization energy is 6910.3 kj/mol. explain why the second and third ionization energies are closer in value than the first and second ionization energies but are not identical to one another.

Explanation:

Sodium (Na) has an electron configuration of \(1s^2 2s^2 2p^6 3s^1\). The first ionization energy removes the \(3s^1\) electron, moving Na to a \(1s^2 2s^2 2p^6\) (noble gas - like) configuration. Removing the second electron requires taking an electron from the stable \(2p^6\) shell, so there's a large jump (from 495.8 kJ/mol to 4562 kJ/mol) as the atom resists losing an electron from a filled shell. After the second electron is removed (configuration \(1s^2 2s^2 2p^5\)), the third ionization energy involves removing an electron from the \(2p^5\) sub - shell. Both the second and third ionization energies are now dealing with electrons in the \(n = 2\) shell (the \(L\) shell), so the energy differences between them are smaller (closer in value) than the jump from \(n = 3\) to \(n = 2\) (first to second). However, they aren't identical because the \(2p^5\) sub - shell has a different electron - electron repulsion and effective nuclear charge compared to the \(2p^6\) sub - shell (from which the second electron was removed), so the energy required to remove an electron from \(2p^5\) (third ionization) is different from removing from \(2p^6\) (second ionization).

Answer:

Sodium's electron configuration is \(1s^2 2s^2 2p^6 3s^1\). The first ionization energy removes the \(3s^1\) electron (easy, small energy). The second removes an electron from the stable \(2p^6\) shell (large energy jump). The second and third ionization energies involve removing electrons from the \(n = 2\) shell (so closer in energy), but not identical as \(2p^5\) (after second ionization) and \(2p^6\) (before second ionization) have different electron - related properties (repulsion, effective nuclear charge).