Formula unit
One Mg for one O does not imply a discrete diatomic molecule.
The solid repeats magnesium–oxygen interactions through a three-dimensional lattice.
Extended solid · basic oxide
Magnesium oxide
MgO
Magnesium oxide is MgO, an extended magnesium–oxygen solid with a 1:1 stoichiometric ratio. Charge bookkeeping assigns Mg as +2 and oxide as −2.
Structure rule: bulk MgO is not a collection of discrete MgO molecules. It forms an extended crystal lattice.
Essentials
MgO is a 1:1 formula unit for an extended solid.
The simplest charge model pairs Mg²⁺ and O²⁻ contributions. That explains stoichiometry without inventing a two-atom molecule in the bulk solid.
Detail
Bulk MgO adopts the rock-salt structure.
In the ideal crystal, each Mg center has six nearest oxygen neighbors and each oxygen has six nearest magnesium neighbors.
Bonding model
Ionic language is useful but not infinitely literal.
Strong electrostatic character dominates, while real electron density is still continuous and polarizable.
Understand
Magnesium oxide behaves as a basic oxide.
Its oxide-rich surface can react with water and acids. The compact equation with water connects MgO conceptually to magnesium hydroxide.
Oxide vs hydroxide
MgO and Mg(OH)₂ are different compounds.
Hydration changes the formula and introduces hydroxide groups rather than merely wetting an unchanged MgO molecule.
Reference identifiers
Names and identifiers that pin down the chemical identity.
| Formula | MgO |
|---|---|
| CAS Registry Number | 1309-48-4 |
| Common bulk structure | rock-salt type |
Advanced
Push past the first model without losing the simple picture.
Is MgO a molecule?
Not in ordinary bulk solid magnesium oxide; MgO is a formula unit for an extended lattice.
Why is the coordination number six?
The rock-salt structure places six oppositely charged nearest neighbors around each ion in the ideal bulk crystal.
Why call MgO a basic oxide?
Oxide sites can accept protons, so MgO reacts with acids and can form hydroxide-related products with water.
Constituent elements