Ionic Bonding | Chemistry

📖 In-Depth Theory

How Ionic Bonds Form

IONIC BONDING occurs between a METAL and a NON-METAL.

The process:

1. The metal atom LOSES one or more electrons from its outer shell.

2. The non-metal atom GAINS those electrons into its outer shell.

3. Both atoms now have FULL OUTER SHELLS — stable noble gas configurations.

4. The metal becomes a POSITIVE ION (it lost negative electrons → net positive).

5. The non-metal becomes a NEGATIVE ION (it gained negative electrons → net negative).

6. OPPOSITE CHARGES ATTRACT — a strong electrostatic force holds the ions together.

This electrostatic attraction between oppositely charged ions IS the ionic bond.

The ions arrange themselves into a regular 3D lattice structure — many ions alternating positive and negative in a giant ionic lattice.

Using Dot-and-Cross Diagrams

DOT-AND-CROSS diagrams show which atoms the electrons came from.

Convention: use dots (•) for electrons from one atom and crosses (×) for electrons from another.

SODIUM CHLORIDE (NaCl):

Na: 2.8.1 — loses its 1 outer electron → becomes Na⁺ (2.8)

Cl: 2.8.7 — gains 1 electron → becomes Cl⁻ (2.8.8)

MAGNESIUM OXIDE (MgO):

Mg: 2.8.2 — loses 2 outer electrons → becomes Mg²⁺ (2.8)

O: 2.6 — gains 2 electrons → becomes O²⁻ (2.8)

MAGNESIUM CHLORIDE (MgCl₂):

Mg: loses 2 electrons → Mg²⁺

Each Cl gains 1 electron → each becomes Cl⁻

2 chloride ions are needed per magnesium (to accept both electrons).

Formula: MgCl₂

Predicting Ion Charges from Group Number

You can predict the charge on an ion from its GROUP in the periodic table:

GROUP 1 metals → lose 1 electron → +1 ions (Li⁺, Na⁺, K⁺)

GROUP 2 metals → lose 2 electrons → +2 ions (Mg²⁺, Ca²⁺)

GROUP 3 metals → lose 3 electrons → +3 ions (Al³⁺)

GROUP 5 non-metals → gain 3 electrons → −3 ions (N³⁻, P³⁻)

GROUP 6 non-metals → gain 2 electrons → −2 ions (O²⁻, S²⁻)

GROUP 7 non-metals → gain 1 electron → −1 ions (F⁻, Cl⁻, Br⁻, I⁻)

The OVERALL CHARGE of an ionic compound must be ZERO — positive and negative charges balance.

For MgCl₂: Mg²⁺ needs 2 Cl⁻ to balance (2+ and 2×1− = 0). ✓

For Al₂O₃: 2 Al³⁺ (6+) needs 3 O²⁻ (6−) to balance. ✓

⚠️ Common Mistake

The IONIC BOND is the electrostatic attraction between OPPOSITELY charged ions — NOT the transfer of electrons itself. The transfer creates the ions; the attraction between them IS the bond. Also: ionic compounds always have an overall charge of ZERO — the positive and negative charges must balance.

📌 Key Note

Ionic bonding: metal loses electrons → positive ion. Non-metal gains electrons → negative ion. Opposite charges attract → ionic bond. Both achieve full outer shells. Group number tells you charge: Group 1 → +1, Group 7 → −1 etc. Overall compound charge = zero.

🎯 Matching Activity — Match the Ion to its Charge

Match each element to the ion it forms and why. — drag the symbols on the right to match the component names on the left.

Sodium (Group 1)

Drop here

Magnesium (Group 2)

Drop here

Chlorine (Group 7)

Drop here

Oxygen (Group 6)

Drop here

Aluminium (Group 3)

Drop here

Al³⁺ — loses 3 electrons to achieve noble gas configuration

Cl⁻ — gains 1 electron to achieve noble gas configuration

O²⁻ — gains 2 electrons to achieve noble gas configuration

Na⁺ — loses 1 electron to achieve noble gas configuration

Mg²⁺ — loses 2 electrons to achieve noble gas configuration

🎯 Test Yourself

Question 1 of 2

1. When sodium (2.8.1) reacts with chlorine (2.8.7) to form NaCl, what happens?

2. What is the formula of calcium chloride? (Calcium is Group 2, Chlorine is Group 7)

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🧪 Ionic Bonding

How Ionic Bonds Form

Using Dot-and-Cross Diagrams

Predicting Ion Charges from Group Number

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