Structure of ionic compounds

Giant ionic lattices
Each ion attracts oppositely charged ions from all directions

• Each ion is surrounded by oppositely charged ions.
• The ions attract each other, forming a giant ionic lattice. 

Properties of ionic compounds
High melting point and boiling point

• Ionic compounds are solids at room temperature
• A large amount of energy is required to break the strong electrostatic forces that hold the oppositely charged ions together in the solid lattice. For this reason, ionic compounds have high melting and boiling points 

Electrical conductivity
In a solid ionic lattice, the ions are in a fixed position and no ions can move. The ionic compound is a non-conductor of electricity. When an ionic compound is melted or dissolved in water, the solid lattice breaks down and the ions are free to move. The ionic compound is now a conductor of electricity.

Solubility
The ionic lattice dissolves in polar solvents, such as water.
The polar water molecules break down the lattice by surrounding each ion to form a solution.

Covalent compounds
Types of structures include a simple molecular lattice and a giant covalent lattice. A simple molecular lattice is a 3D structure of molecules, bonded together by weak intermolecular forces. A giant covalent lattice is a 3D structure of atoms, boneded together by strong covalent bonds.  

Simple molecular structures
Simple molecular structures are made up from small, simple molecules, such as Ne, H2, O2, N2 and H2O. In a solid molecular lattice molecules are held together by weak forces between molecules. The atoms within each molecule are bonded together by covalent bonds.  

The simple molecular structure of Iodine. The different forces within the simple molecular structure of solid I2 are covalent bonds and van der Waals'. The atoms are held together by covalent bonds, and there are van der Waals' forces between the I2 molecules.  

Properties of simple molecular structures
Low melting and boiling point
Simple molecular structures have low melting and boiling points because the intermolecular forces are weak van der Waals' forces, so a relatively small amount of energy is needed to break them.

Electoral conductivity
Simple molecular structures are non-conductors of electricity because there are no charged particles free to move.

Solubility
Simple molecular structures are soluble in non-polar solvents, such as hexane. This is because van der Waals' forces form between the simple molecular structures and the non-polar solvent.  The formation of these van der Waals' forces weakens the lattice structure. 

Giant covalent structures.
Diamond, graphite and SiO2 are examples of a giant covalent structure. 

Properties of giant covalent
High melting and boiling points
Giant covalent structures have high melting and boiling points because high temperatures are needed to break the strong covalent bonds in the lattice.

Electoral conductivity
Giant covalent structures are non-conductors of electricity because there are no free charged particles except in graphite.

Solubility.
Giant covalent structures are insoluble in both polar and non-polar solvents because the covalent bonds in the lattice are too strong to be broken by either polar or non-polar solvents. 

Diamond
Structure - Tetrahedral structure held together by strong covalent bonds throughout the lattice.
Electoral conductivity - Poor conductivity. There are no delocalised electrons as all outer-shell electrons are used for covalent bonds
Hardness - Hard. Tetrahedral shape allows external forces to be spread throughout the lattice.

Graphite
Structure - Strong hexagonal layer structure, but with weak van der Waals' forces between the layers
Electoral conductivity - Good conductivity. There are delocalised electrons between layers. Electrons are free to move parallel to the layers when a voltage is applied.
Hardness - Soft. Bonding within each layer is strong. Weak forces between layers allows layers to slide easily.