Ions: Formation, Types & Ionic Compounds

IONS – Key Notes

What is an ion?

• An ion is any atom or group of atoms that carries an electric charge.
• Ions are formed when an atom gains or loses electrons.
• An atom becomes an ion when the number of protons ≠ electrons.

TYPES OF IONS

1️⃣ Cations

• Cations are positively charged ions (+).
• Formed when an atom loses electrons.
• Usually formed by metals found on the left side of the periodic table.
• Example:
  • Na → Na⁺ + e⁻
  • Mg → Mg²⁺ + 2e⁻

Why are metals cations?

• Metals have 1, 2, or 3 valence electrons, which they easily lose.
• The charge of metallic cations in:
  • Group I = +1
  • Group II = +2
  • Group III = +3

2️⃣ Anions

• Anions are negatively charged ions (–).
• Formed when an atom gains electrons.
• Usually formed by non-metals on the right side of the periodic table.
• Examples:
  • Cl + e⁻ → Cl⁻
  • O + 2e⁻ → O²⁻

Why are non-metals anions?

• Non-metals need electrons to fill their valence shell.
• The charge of an anion = number of electrons gained
  • Group 17 → gains 1 → charge = –1
  • Group 16 → gains 2 → charge = –2

HOW IONS FORM COMPOUNDS

• Metals give electrons to non-metals.
• Metal becomes cation (+)
• Non-metal becomes anion (–)
• They combine through ionic bonding.

EXAMPLES OF ION FORMATION & COMPOUND FORMATION

1️⃣ Magnesium reacts with Chlorine

Mg + 2Cl → Mg²⁺ + 2Cl⁻ → MgCl₂

Explanation:

• Mg loses 2 electrons → Mg²⁺
• Each Cl gains 1 electron → Cl⁻
• Ratio becomes 1 Mg²⁺ : 2 Cl⁻

2️⃣ Sodium reacts with Chlorine

Na + Cl → Na⁺ + Cl⁻ → NaCl

Explanation:

• Na loses 1 electron → Na⁺
• Cl gains 1 electron → Cl⁻
• Combine in 1:1 ratio to form NaCl

SHORT SUMMARY

• Ion: charged atom or group of atoms
• Cation: positive ion (lost electrons; usually metal)
• Anion: negative ion (gained electrons; usually non-metal)
• Metals → cations
• Non-metals → anions
• Ionic compounds form when metals transfer electrons to non-metals

How to Decide Ionic vs Molecular

• Ionic compounds = metal + non-metal (involves ions)
• Molecular compounds = non-metal + non-metal (share electrons; covalent)

a. KI (Potassium iodide)

• K = potassium → metal
• I = iodine → non-metal
  ➡️ Ionic compound

This is why KI dissolves in the body to release iodide ions.

b. H₂O₂ (Hydrogen peroxide)

• H = hydrogen → non-metal
• O = oxygen → non-metal
  ➡️ Molecular compound

This compound is made of covalently bonded atoms.

c. CHCl₃ (Chloroform)

• C = carbon → non-metal
• H = hydrogen → non-metal
• Cl = chlorine → non-metal
  ➡️ Molecular compound

No metals present → must be molecular.

d. Li₂CO₃ (Lithium carbonate)

• Li = lithium → metal
• CO₃²⁻ = carbonate polyatomic ion → non-metal-based ion
  ➡️ Ionic compound

Lithium ion (Li⁺) + carbonate ion (CO₃²⁻).

✅ Final Answers Table