Chemical Bonding

Atoms can chemically bond (join together) in 3 ways: ionic bonding, covalent bonding or metallic bonding.

Ionic bonds are made between two oppositely charged ions of metals and non-metals. 

Covalent bonds are found in most non-metal elements and compounds where 2 atoms share 1 or more pairs of electrons.

Metallic bonding is found in metals and alloys and involves an attraction between positively charged ions and negatively charged delocalised electrons.

Ions are particles that have a charge - they are created when an atom or molecule gains or loses electrons. Gaining electrons creates a negatively charged ion; losing electrons creates a positively charged ion.

Positive ions are called cations. The metals in group 1/2 can easily lose electrons.

Negative ions are called anions. The non-metals in group 7 are likely to gain electrons. 

Ionic bonds usually only conduct electricity when molten and have a high melting point.

Ionic compounds form when millions of metal atoms transfer their outer electrons to millions of non-metal atoms at the same time. The resulting oppositely charged ions are held together in ionic lattices.

Ionic lattices are structures that are held together by strong electrostatic forces between the positive and negative ions

The electrostatic forces are called ionic bonds.

Ionic compounds can be shown with dot and cross diagrams - these show electrons being transferred and ions being formed. 

Covalent bonds are formed when 2 non-metal atoms share pairs of electrons. Covalent bonds are strong because the shared electrons are attracted to the nucleus of both atoms.

Metallic bonds are the electrostatic attractions between positive ions and negatice delocalised electrons.

Metals are giant structures of regularly arranged atoms. The structures is a regular lattice of cations in a 'sea' of delocalised electrons. Delocalised electrons are not bound to an atom and are free to move around withing the lattice. Delocalisation occurs because metal atoms have a smaller number of electrons in their outer shells.