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Year 11 Science

Chemical Bonding

Understand the three main types of chemical bonds -- ionic, covalent and metallic -- and how Lewis dot structures and electronegativity differences help predict bond type and polarity.

Ionic Bonding

An ionic bond forms when one or more electrons are transferred from a metal to a non-metal. The metal becomes a positively charged cation, and the non-metal becomes a negatively charged anion. The electrostatic attraction between opposite charges holds them together.

Ionic Bond Formation: NaCl

Na

2, 8, 1

Loses 1 electron

→

Na+

2, 8

Stable octet

+

Cl-

2, 8, 8

Stable octet

Properties of ionic compounds: High melting/boiling points, conduct electricity when molten or dissolved in water (ions are free to move), form crystal lattice structures, brittle solids at room temperature.

Covalent Bonding

A covalent bond forms when two non-metal atoms share one or more pairs of electrons. Each shared pair constitutes one covalent bond. Atoms share electrons to achieve a stable outer shell (usually 8 electrons -- the octet rule).

Lewis Dot Structures

H2 (Single bond)

H -- H

1 shared pair of electrons

O2 (Double bond)

O = O

2 shared pairs of electrons

N2 (Triple bond)

N ≡ N

3 shared pairs of electrons

Polar Covalent Bond

Electrons are shared unequally between atoms with different electronegativities. The more electronegative atom has a partial negative charge (δ-). Example: H-Cl

Non-polar Covalent Bond

Electrons are shared equally between atoms with the same or very similar electronegativities. Example: O=O, H-H, Cl-Cl

Metallic Bonding and Bond Comparison

In metallic bonding, metal atoms release their valence electrons to form a "sea" of delocalised electrons. These free-moving electrons are shared among all the metal cations in the lattice, creating a strong bond.

Metallic Bond Model

+
+
+
+
+
+
+
+

Metal cations (+) surrounded by a "sea" of delocalised electrons (yellow background)

Comparing Bond Types

Feature Ionic Covalent Metallic
Between Metal + non-metal Non-metal + non-metal Metal + metal
Electrons Transferred Shared Delocalised
Conducts electricity When molten/dissolved Usually not Yes (solid & liquid)
Melting point High Low to moderate Variable (often high)

Key Vocabulary

Ionic Bond

A bond formed by the electrostatic attraction between oppositely charged ions, resulting from the transfer of electrons from a metal to a non-metal.

Covalent Bond

A bond formed by the sharing of one or more pairs of electrons between two non-metal atoms.

Lewis Structure

A diagram showing the bonding pairs and lone pairs of electrons around atoms in a molecule, using dots or lines.

Octet Rule

The tendency of atoms to bond in such a way that each has 8 electrons in its valence shell (except hydrogen, which aims for 2).

Worked Examples

1

Predict the type of bonding in MgO.

Mg is a metal (Group 2), O is a non-metal (Group 16).

Metal + non-metal = ionic bonding.

Mg loses 2 electrons to form Mg2+. O gains 2 electrons to form O2-. Both achieve stable octets.

2

Draw the Lewis structure for water (H2O).

Oxygen has 6 valence electrons. Hydrogen has 1 each.

O shares 1 electron with each H (2 bonding pairs), leaving 2 lone pairs on O.

Structure: H--O--H with 2 lone pairs on the oxygen. Total: 8 electrons around O (octet satisfied), 2 around each H.

3

Is the bond in HCl polar or non-polar?

Electronegativity: H = 2.2, Cl = 3.2

Difference: 3.2 - 2.2 = 1.0

A difference between 0.4 and 1.7 indicates a polar covalent bond. The shared electrons are pulled toward chlorine (δ- on Cl, δ+ on H).

Knowledge Check

Select the correct answer for each question. Click "Check Answer" to see if you are right.

Question 1

Ionic bonds typically form between:

Question 2

In a covalent bond, atoms achieve stability by:

Question 3

Which of these molecules contains a double covalent bond?

Question 4

Metallic bonding involves:

Question 5

A polar covalent bond forms when:

Key Concepts Summary

Year 11: Periodic Table Trends Year 11: Cell Structure