Structures and Properties AQA Additional Science Chemistry

Ionic compounds have giant structures in which many strong electrostayic forces hold the ions tightly together.

They are solids at room temperature.

Ionic compounds have high melting and boiling points.

When they have been melted the ions are free to move. This allows them to carry electrical charge, so the liquids conduct electricity.

Some ionic solids dissolve in water because water molecules can split up the lattice.

The ions are free to move in the solutions and so they also conduct electricity.

Ionic compounds conduct electricity when molten or in solution.

The atoms in molecules are held together by strong covalent bonds. These bonds act only between the atoms within the molecule, and so simple molecules have little attraction for each other. Substances made of simple molecules have relatively low melting and boiling points. Molecules have no overall charge and cannot carry an electric current, so these substances do not conduct electricity.

The forces between simple molecules are weak so many of these substances are gases or liquids at room temperature. Simple molecules do not have a charge and so cannot conduct electricity.

Metal atoms are arranged in layers and if a force is applied the layers of atoms can slide over each other. This makes them change into a new position without it breaking. The metal can bend, stretch and change shape. These metals are good for making wires, rods and sheet materials.

Metals can be bent and shaped because their layers of atoms can slide over each other. Delocalised electrons move throughout metals and can carry heat and electricity.

Atoms of some elements can form several covalent bonds.

These atoms can join together in giant covalent structures (sometimes called 'macromolecules').

Every atom in the structure is joined to several other atoms by strong covalent bonds. It takes an enormous amount of energy to break down the lattice and so these substances have very high melting points.

Some covalently bonded substances form giant structures.

These substances have very high melting points.

Diamond and graphite are both forms of carbon but have many different properties.

Atoms are arranged in very small particles which behave differently to ordinary materials made of the exact same atoms.

A nanometre is one billionth of a metre and nano particles are a few nanometres in size. A few hundred atoms are arranged here in a particular way. Their structure and very small sizes give them new properties that can make them very useful materials.

Nano particles have very large surface areas, exposing many more atoms at their surface than normal materials. Electrons can move through them more easily than ordinary materials. They can be very sensitive to light, heat,pH, electricity and magnetism.

Nanotechnology uses nano particles as very sensitive sensors, highly efficient catalysts, new coatings and construction materials with special properties, and to make drugs more effective.