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*Revision Materials* 1 Atomic Structure 2 Atoms, molecules and stoichiometry 3 Chemical Bonding 4 States of matter 5 Chemical energetics 6 Electrochemistry 7 Equilibria 8 Reaction kinetics 9 The Periodic Table, chemical periodicity 10 Group 2 11 Group 17 12 Nitrogen and sulfur 13 Organic 14 Hydrocarbons 15 Halogen compounds 16 Hydroxy compounds 17 Carbonyl compounds 18 Carboxylic acids and derivatives 19 Nitrogen compounds 20 Polymerisation 21 Organic synthesis 22 Analytical techniques 23 Chemical energetics 24 Electrochemistry 25 Equilibria 26 Reaction kinetics 27 Group 2 28 Chemistry of transition elements 29 Organic 30 Hydrocarbons 31 Halogen compounds 32 Hydroxy compounds 33 Carboxylic acids and derivatives 34 Nitrogen compounds 35 Polymerisation 36 Organic synthesis 37 Analytical techniques

3 Chemical Bonding

3.1 Electronegativity and bonding 3.2 Ionic bonding 3.3 Metallic Bonding 3.4 Covalent bonding and coordinate (dative covalent) bonding 3.5 Shapes of molecules 3.6 Intermolecular forces, electronegativity and bond properties 3.7 Dot-and-cross diagrams

Dot-and-Cross Diagrams

Specification Reference Physical Chemistry: Chemical bonding 3.7

Quick Notes

  • Dot-and-cross diagrams show the outer electrons involved in bonding, using either dots or crosses to represent electrons from different atoms.
  • We can use them to show:
    • Forming of ions for ionic bonding (transfer of electrons)
    • Covalent bonding (shared electrons)
    • Coordinate (dative covalent) bonding (shared electrons both from the same atom)

Full Notes

What is a Dot-and-Cross Diagram?

A dot-and-cross diagram is a way to represent bonding in a compound. It shows:

They help visualise:

Ionic Bonding in Dot-and-Cross Diagrams

In ionic bonding:

Example Sodium chloride (NaCl)

Dot-and-cross diagram showing sodium chloride electron transfer and ions in square brackets.

Covalent Bonding in Dot-and-Cross Diagrams

In covalent bonding:

Examples of molecules with Single bonds (1 shared pair):

Dot-and-cross diagrams of molecules with single covalent bonds.

Examples of molecules with Double bonds (2 shared pairs):

Dot-and-cross diagrams of molecules with double covalent bonds.

Examples of molecules with Triple bonds (3 shared pairs):

Dot-and-cross diagram of nitrogen molecule with triple covalent bond.

Coordinate (Dative Covalent) Bonding

In coordinate bonding both electrons in the shared pair come from one atom.

Examples of co-ordinate bonding:

Dot-and-cross diagrams showing coordinate bonding in NH4+ and Al2Cl6.

Expanded Octets

Some elements (usually in Period 3 or below) can hold more than 8 electrons.

Examples:

Dot-and-cross diagrams showing expanded octets in SO2, PCl5, SF6.

Molecules with an Odd Number of Electrons

Some species (called free radicals) have an unpaired electron.

Example NO (nitric oxide): total of 11 outer electrons → one electron will remain unpaired in the diagram.

Dot-and-cross diagram of nitric oxide radical with unpaired electron.
Photo of Matt
Matt’s exam tip

You should show an unpaired electron clearly, usually as a single dot or cross without a pair. Make it obvious and clear it is a radical.

Summary