An oxide ion (O^2-) is formed when an oxygen atom gains two electrons. Here's a breakdown of the process:

* Oxygen's Electronic Configuration: A neutral oxygen atom has 8 electrons, with the electronic configuration 1s² 2s² 2p⁴. This means it has 6 electrons in its outer shell (the valence shell).

* Desire for Stability: Oxygen, like most elements, wants to achieve a stable electron configuration. This means having a full outer shell of 8 electrons.

* Gaining Electrons: To achieve this, oxygen can gain two electrons, becoming an anion (negatively charged ion).

* Formation of Oxide Ion: When oxygen gains these two electrons, it fills its outer shell and becomes the oxide ion (O^2-).

Here's a simplified visual:

```

O + 2e- → O²⁻

```

Key Points:

* The formation of oxide ions is a common process in chemistry, particularly in the formation of ionic compounds.

* The oxide ion carries a 2- charge due to gaining two negatively charged electrons.

* This process is an example of electron affinity, where an atom gains electrons to achieve a more stable electronic configuration.