Chemistry - Structure and Properties

- An ionic compound consists of a structure (sometime giant) of ions arranged in a lattice. The electrostatic forces between the oppositely charged ions are very strong and hold the ions together very tightly.

- The ionic lattice needs a lot of energy to break the bonds between the atoms.

- However, once the bonds are broken the ionic solid becomes a liquid. The ions are free to move and are able to conduct electricity, which the solid ionic compound cannot.

- Many ionic compounds also dissolve in water. The lattice is split up and the ions are free to move. They are also able to conduct electricity.

- When two non-metal elements react to form a compound, covalent bonds are formed as they share electrons in their outer shells.

- Substances made up of covalently bonded molecules tend to have low melting points and boiling points. This means that many substances with simple molecules are liquids or gases at room temperature.

- Although a substance that is made up of simple molecules may be a liquid at room temperature, it will not conduct electricity.

- Because there is no overall charge on the molecules in a simple covalent compound, the molecules cannot carry electric charge.

- Most non-metals react and form covalent bonds which join the atoms together in molecules, but a few form different structures. Instead of joining a small number of atoms together in individual molecules, the covalent bonds form large networks of covalent bonds, called giant covalent structures.

- These substances have high melting and boiling points, and very hard and very unreactive.

- Diamond and graphite (lead) are examples of giant covalent structures.

- We can bend and shape metals becauese the layers of atoms (or ions) in a metal can slide over each other.

- If we introduce another element to the metal we create an alloy. The atoms in an alloy are different sized so it makes it harder for the atoms to slide over each other.

- Delocalised electrons in metals allow them to conduct heat and electricity well.