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💡 Cation first, anion second
Read an ionic name like a small sentence: name the positive ion first, then the negative one ending in -ide. Meet the common ions in the tables below.
How are ionic compounds named?
Naming Ionic Compounds
Name the cation first Simple anion ends in -ide Metals form cations, non-metals anions Polyatomic ions are multi-atom ions
- Name the cation first , then the anion .
- Simple anions end in -ide (chloride, oxide, sulfide).
- Metals usually form cations ; non-metals form anions .
- Ions made of two or more atoms are polyatomic ions (e.g. sulfate, nitrate).
| Name of ion | Formula | Valency |
|---|---|---|
| Sodium | Na⁺ | 1 |
| Lithium | Li⁺ | 1 |
| Potassium | K⁺ | 1 |
| Silver | Ag⁺ | 1 |
| Calcium | Ca²⁺ | 2 |
| Barium | Ba²⁺ | 2 |
| Iron (Ferrous) | Fe²⁺ | 2 |
| Iron (Ferric) | Fe³⁺ | 3 |
| Copper (Cuprous) | Cu⁺ | 1 |
| Copper (Cupric) | Cu²⁺ | 2 |
| Magnesium | Mg²⁺ | 2 |
| Zinc | Zn²⁺ | 2 |
| Aluminium | Al³⁺ | 3 |
| Fluoride | F⁻ | 1 |
| Chloride | Cl⁻ | 1 |
| Bromide | Br⁻ | 1 |
| Iodide | I⁻ | 1 |
| Oxide | O²⁻ | 2 |
| Sulfide | S²⁻ | 2 |
| Name of ion | Formula | Valency |
|---|---|---|
| Hydroxide | OH⁻ | 1 |
| Nitrate | NO₃⁻ | 1 |
| Hydrogencarbonate | HCO₃⁻ | 1 |
| Carbonate | CO₃²⁻ | 2 |
| Sulfate | SO₄²⁻ | 2 |
| Ammonium | NH₄⁺ | 1 |
⏸▶ Pause and Ponder
- 12. Oxygen has 6 valence electrons, so it gains 2 to form the oxide ion O²⁻ (an anion).
- 13. Chlorine takes one electron to become chloride (Cl⁻) . One ion of magnesium (Mg²⁺) and two ions of chloride combine to give MgCl₂.
- 14. K → K⁺ and Ca → Ca²⁺; their chlorides are KCl and CaCl₂ (shown with electron-transfer diagrams).
- 15. Na₂S: two Na⁺ ions each give one electron to one S²⁻ ion.
❓ What if…
- What if we could see atoms directly?
- Identifying materials would become far easier for scientists.
- But the tools needed are electron microscopes.
- They are complex, delicate and very costly.
- That is a real scientific challenge.
✅ Test Yourself
-
Define a molecule.
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An electrically neutral entity of more than one atom that can exist independently. -
What is a covalent bond?
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A bond formed by the sharing of a pair of electrons between atoms. -
What is an ionic bond?
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The electrostatic force of attraction between oppositely charged ions. -
How many pairs of electrons are shared in O₂?
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Two pairs — a double bond, O=O. -
What is the valency of the chloride ion Cl⁻?
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1.
Important Definitions
- Monoatomic ions — ions made of a single atom, e.g. Na⁺, Cl⁻, O²⁻.
- Polyatomic ions — ions made of two or more atoms, e.g. sulfate SO₄²⁻, nitrate NO₃⁻.
