Two atoms have the electron configurations \(1 s^{2} 2 s^{2} 2 p^{6}\) and \(1 s^{2} 2 s^{2} 2 p^{6} 3 s^{1} .\) The first ionization energy of one is \(2080 \mathrm{~kJ} / \mathrm{mol}\), and that of the other is \(496 \mathrm{~kJ} / \mathrm{mol} .\) Match each ionization energy with one of the given electron configurations. Justify your choice.

Understanding electron configuration is essential to grasp the concept of first ionization energy. Electron configuration refers to the distribution of electrons in an atom's orbitals. It is depicted by a series of numbers, letters, and superscripts that indicate the principal energy levels (n), sublevels (s, p, d, f), and the number of electrons in those sublevels.

For example, the electron configuration of Neon is represented as \(1s^2 2s^2 2p^6\). This shows that Neon has two electrons in the 1s orbital, two in the 2s orbital, and six in the 2p orbitals, completely filling the first and second energy levels. This full outer shell is what gives elements like Neon their chemical stability, contributing to a higher first ionization energy.

Noble gases, which include elements like Neon, have full valence electron shells, making them extremely stable. Because of this stability, they rarely engage in chemical reactions. This stability is also mirrored in their high first ionization energies. The ionization energy is the energy required to remove the most loosely bound electron, and since noble gases have no loosely bound electrons, the amount of energy needed is significant. This explains why the ionization energy of Neon is a sizable \(2080 \text{ kJ/mol}\).

Noble gases’ full outer shells make them nonreactive, and in terms of their electron configurations, they are often considered to be the benchmark for chemical stability.

Alkali metals, such as Sodium, which have the electron configuration ending in \(s^1\), are characterized by having one electron in their outermost shell. This single valence electron is more loosely bound compared to electrons in noble gases, making alkali metals highly reactive. They are eager to donate this electron in chemical reactions to achieve a full outer shell, similar to noble gases. Their inclination to lose an electron results in a much lower ionization energy.

The electron configuration of Sodium is \(1s^2 2s^2 2p^6 3s^1\), indicating a lone electron in the 3s orbital. Therefore, an ionization energy of \(496 \text{ kJ/mol}\) is sufficient to remove this electron, which is considerably lower than the ionization energy for noble gases.

Chemical stability is a fundamental concept in chemistry, describing the reluctance of a chemical species to react or to change its structure. Atoms with full valence electron shells, like the noble gases, exhibit exceptional chemical stability because their electron configurations are energetically favorable.

In contrast, atoms with incomplete valence shells, such as alkali metals, tend to be less stable and more reactive. They seek to either donate or accept electrons to achieve a stable electron configuration, which is typically a full octet in the outermost shell. The ionization energy is a clear indicator of this stability - a high ionization energy correlates with greater chemical stability, as seen in noble gases, while a low ionization energy points to a propensity for change and reactivity, as demonstrated by alkali metals.