Two bonding levels
Ionic between sodium and carbonate; covalent inside carbonate.
The C–O framework belongs to the polyatomic ion.
Ionic solid · carbonate salt
Sodium carbonate
Na₂CO₃
Sodium carbonate is Na₂CO₃, an ionic solid made from Na⁺ and CO₃²⁻ ions. Two sodium ions are required for each carbonate ion to balance charge.
Hydrate distinction: sodium carbonate can occur in hydrated crystal forms. This master describes the anhydrous composition Na₂CO₃ unless a hydrate is named explicitly.
Essentials
Na₂CO₃ is two Na⁺ ions for one CO₃²⁻ ion.
The formula unit is charge-balanced. It should not be drawn as one six-atom covalent molecule.
Detail
The carbonate ion is trigonal planar and resonance-delocalized.
A single Lewis contributor cannot make all three C–O positions equivalent. Resonance is the correct bookkeeping language for the isolated carbonate ion.
Do not invent Na–O molecules
Sodium ions belong to the extended ionic solid.
The formula records composition, not a discrete molecular geometry for Na₂CO₃.
Understand
Acid converts carbonate into carbon dioxide and water.
Protons consumed by carbonate ultimately give CO₂ and H₂O, which explains effervescence when carbonate contacts acid.
Compare bicarbonate
CO₃²⁻ and HCO₃⁻ differ by one proton and one charge unit.
Sodium carbonate and sodium bicarbonate are therefore distinct compounds with different stoichiometry and acid–base behavior.
Reference identifiers
Names and identifiers that pin down the chemical identity.
| Formula | Na₂CO₃ |
|---|---|
| CAS Registry Number | 497-19-8 |
| Form represented | anhydrous sodium carbonate |
Advanced
Push past the first model without losing the simple picture.
Is sodium carbonate a molecule?
No. In the solid it is an extended ionic material represented by formula units.
Why are three C–O positions equivalent in carbonate?
Resonance and trigonal symmetry delocalize the bonding across the three oxygen positions.
Is washing soda the same formula as anhydrous sodium carbonate?
Not necessarily. Washing soda commonly refers to hydrated sodium carbonate, so the water of crystallization must be specified.
Constituent elements