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

The Octet Rule is fundamental to understanding chemical bonding and stability. It refers to the tendency of atoms to prefer having eight electrons in their valence shell, the outermost electron orb. This rule is based on the observation that atoms with filled valence shells demonstrate similar chemical properties to the noble gases, the naturally occurring elements that are incredibly stable and non-reactive.
By aiming for a full set of eight valence electrons, atoms can achieve greater stability. For instance, in the case of oxygen, which is highlighted in the exercise, the application of the Octet Rule helps to explain this element’s chemical behavior. With six electrons in its valence shell, oxygen is two electrons short of the octet, leading it to gain electrons when forming compounds. The desire for a full octet drives oxygen to form the O²⁻ ion, completing its octet and achieving a more stable, noble gas-like electronic configuration.

Valence electrons play a crucial role in chemical reactivity and are the electrons found in an atom's outermost shell that participate in forming bonds. As illustrated in the exercise, understanding the electron configuration of an element like oxygen is key to analyzing its chemical behavior. With the electron configuration 1s²2s²2p⁴, oxygen has six valence electrons. These are the electrons oxygen uses to interact with other atoms and are the ones considered when applying the Octet Rule.
Valence electrons determine an atom's ability to gain, lose, or share electrons to form chemical bonds. Elements in the same group of the periodic table usually have the same number of valence electrons, contributing to similarities in their bonding characteristics. This concept is essential because the number of valence electrons impacts the type and strength of the bonds an atom can form.

Ion formation occurs when an atom gains or loses electrons, resulting in a charged particle known as an ion. The charge on the ion depends on whether the atom loses electrons (becoming a positively charged cation) or gains electrons (becoming a negatively charged anion), as seen in the exercise solution for oxygen. The driver behind ion formation is the quest for stability; atoms modify their electron count to resemble the electron configuration of the nearest noble gas.

Oxygen's Path to Ionization

Oxygen commonly forms an anion by gaining two electrons to complete its octet. This process creates an oxide ion (O²⁻), which has two more electrons than protons, hence the 2- charge. In ionic compounds, oxygen's tendency to form a 2- anion allows it to bond with elements that can provide it with the two requisite electrons to achieve a stable electron configuration, in line with the Octet Rule. This fundamental action, the creation of an ion, is the crux of many chemical reactions and the formation of compounds.