Use the electron configuration of oxygen to explain why it tends to form a 2 - ion.

Valence electrons are the electrons that reside in the outermost shell of an atom; they are essential in determining an element's chemical properties and its ability to bond with other elements. For oxygen, a member of the chalcogen family, the valence shell is the second shell which includes the 2s and 2p orbitals. In its ground state, an oxygen atom has a total of six valence electrons; two occupying the 2s orbital and four in the 2p orbital. Oxygen's valence electrons are crucial in predicting its behavior in chemical reactions because elements tend to react in ways that will fill their valence shell, mimicking the stability of noble gases. Since oxygen is six electrons short of filling its valence shell—needing eight in total for stability—it will often form compounds that allow it to gain the additional two valence electrons it requires.

An understanding of valence electrons is a launchpad into deeper chemical comprehension, such as predicting molecular shapes, understanding reactivity, and even the formation of ions, as is the case with oxygen anion formation.

An anion is formed when an atom gains electrons, resulting in a net negative charge. In the case of oxygen, the formation of an anion is a response to its need for stability. As we've established that oxygen naturally has six valence electrons, it aims to fill its valence shell with a full octet of eight electrons to achieve a stable electronic arrangement. To reach this full valence shell, oxygen tends to gain two electrons. Upon acquiring these additional electrons through chemical reactions, an oxygen anion (typically represented as O^2-) is born.

The process of anion formation is a significant concept in ionic bonding and electrochemistry. By accepting the electrons, oxygen does not just settle to a lower energy, but also sets the stage for ionic compound formation, where it can bond with cations (positively charged ions) such as those of metals, leading to stable and often crystalline structures such as table salt (sodium chloride) or rust (iron oxide).

The noble gases, occupying the far right column of the periodic table, are celebrated for their low reactivity. This inert behavior is credited to their stable electron configurations, with a full valence shell of electrons. Elements that do not naturally possess a full valence shell often undergo chemical reactions to achieve a noble gas configuration, synonymous with stability and minimization of energy. For oxygen, achieving a stable noble gas configuration means having a full outer shell similar to that of neon, with eight electrons.

By gaining two electrons and becoming an oxide anion (O^2-), oxygen adopts this stable configuration. The desire for stability through a full valence shell, not only explains the reactive nature of certain elements but also dictates the types of bonds that will form. For instance, the pursuit of full valence shells is a fundamental reason behind the formation of covalent and ionic bonds, where electrons are shared or transferred between atoms, respectively. This quest for stability is a driving force in the dynamic world of chemistry and is key to understanding various chemical phenomena.