While the standard molecular oxygen (O₂) is a neutral molecule, the provided reference explains why the oxide ion (O²⁻) carries a charge. This charge arises when an individual oxygen atom gains electrons to achieve a stable electron configuration.
Understanding How the Oxide Ion Gets Its Charge
An oxygen atom naturally seeks stability by filling its outermost electron shell, following the well-known octet rule.
- Valence Electrons: Oxygen is positioned in Group 6 of the periodic table. This means that a neutral oxygen atom possesses six electrons in its valence (outermost) shell.
- Achieving Stability: To attain a full outer shell of eight electrons, similar to a noble gas, an oxygen atom needs to gain two additional electrons.
- The Role of Electron Charge: Each electron carries a negative charge, specifically 1-.
Calculating the Oxide Ion's Charge
When an oxygen atom gains two electrons to fulfill the octet rule, these extra negative charges contribute to the overall charge of the resulting ion.
As the reference states: "Because electrons have a charge of 1-, adding two electrons would make the charge of the oxide ion 2-."
| Species | Number of Protons (typically 8 for Oxygen) | Number of Electrons | Net Charge |
|---|---|---|---|
| Neutral Oxygen Atom | 8 | 8 | 0 |
| Oxide Ion (O²⁻) | 8 | 8 + 2 = 10 | 2- |
Therefore, the oxide ion (O²⁻) has a charge of 2- because it has gained two electrons, each contributing a 1- charge. This is distinct from the neutral diatomic oxygen molecule (O₂) which is formed by the sharing of electrons between two oxygen atoms.
