Chemical bonds

Section 1 of 7Why atoms bond

1Incomplete outer shell

• Incomplete outer shell Most atoms do not have a full outer shell of electrons, so they are not stable on their own.

2Electrons move or are shared

• Electrons move or are shared Atoms rearrange their outer electrons when they react.

3Full outer shell

• Full outer shell Having a full outer shell makes the atoms more stable.

4A bond results

• A bond results The strong attraction that holds the particles together is called a chemical bond.

Section 2 of 7The three types of bonding

Chemical bonding at GCSE

Ionic bonding

• Ionic bonding Occurs between a metal and a non-metal.
• Electrons are transferredthe metal loses electrons to form positive ions and the non-metal gains them to form negative ions.
• Oppositely charged ions attract each other by electrostatic forces.

Covalent bonding

• Covalent bonding Occurs between non-metal atoms.
• Pairs of electrons are shared between the atoms, so both reach a full outer shell.

Metallic bonding

• Metallic bonding Occurs in metals and alloys, which are mixtures of metals.
• Outer electrons are delocalised and the metal ions are held by attraction to them.

Section 3 of 7Comparison

Bond type	Between	What happens to electrons	Result
Ionic	Metal + non-metal	Transferred	Giant lattice of oppositely charged ions
Covalent	Non-metal + non-metal	Shared in pairs	Small molecules or giant covalent structures
Metallic	Metal atoms only (or alloys)	Outer electrons delocalised	Giant lattice of positive ions in a sea of electrons

Section 4 of 7Deciding which bond is present

1

Decide whether each element in the substance is a metal or a non-metal using the Periodic Table.

2

If it contains a metal and a non-metal, the bonding is ionic.

3

If it contains only non-metals, the bonding is covalent.

4

If it contains only metal atoms, or a mixture of metals, the bonding is metallic.

Section 5 of 7Forces between molecules

Not chemical bonds

• Not chemical bonds Intermolecular forces are attractions between separate molecules.
  • No electrons are shared or transferred, and no new substance forms.
• They are much weaker than chemical bonds, about a tenth of the strength.

Section 6 of 7Key terms

Term	Meaning
Chemical bond	A strong force of attraction that holds atoms or ions together in a substance.
Ionic bond	The electrostatic attraction between oppositely charged ions.
Covalent bond	A shared pair of electrons between two atoms.
Metallic bond	The attraction between positive metal ions and delocalised electrons.
Electrostatic force	The force of attraction between opposite charges.
Alloy	A mixture of a metal with other elements, often other metals.

Section 7 of 7Exam technique

1

Saying that ionic bonds involve sharing electrons. Ionic bonding is transfer, covalent is sharing.

2

Describing intermolecular forces as chemical bonds. They are much weaker and no electrons are shared.

3

Claiming covalent bonds occur between a metal and a non-metal. That combination gives ionic compounds.

4

Writing that the bond in an ionic compound is the transfer itself. The bond is the electrostatic attraction between the ions that results.

5

Forgetting that the purpose is to give atoms a full outer shell.