C2.3 - Properties Of Materials

• Carbon can form four covalent bonds. • A carbon atom can join with other carbon atoms and also form covalent bonds with other elements producing many different compounds.

Allotropes are different forms of an element in the same state but with different atomic arrangements.

• Diamond - Transparent very hard 2. Graphite - Grey-black and soft

• Giant covalent structure. • Each carbon atom is covalently bonded to four other carbon atoms. • Many covalent bonds means that diamond has a very high melting point and is very hard - Makes them suitable for the drills of dental drills. • No delocalised electrons - Cannot conduct electricity.

• Giant covalent structure. • Each carbon atom is covalently bonded to just three other carbon atoms. • One electron in the outer shell of each atom is not involved in bonding - Becomes delocalised instead - Free to move throughout the structure and therefore graphite can conduct electricity • Layered structure. • Atoms in each layer form interlocking hexagons. • High MP - Many strong covalent bonds. • Forces between each layer are weak - Layers can slide over each other.

- A carbon allotrope that resembles a single layer of graphite. - Almost transparent. - Extremely strong. - Conducts electricity.

Fullerenes form a large family of carbon allotropes in which the molecules are shapes like tubes or balls. • A nanotube resembles a sheet of graphene rolled into a tube - Strong and used to reinforce sports equipment. • A buckyball resembles a sheet of graphene closed to make a hollow ball - Potential uses as a lubricant - Molecules acting like tiny ball bearings - Could be used for drug delivery systems

• Forces of attraction between its particles are overcome. • Some bonds break going from the solid to liquid state. • Nearly all of the remaining bonds break going from the liquid to the gas state.

• Some bonds form going from the gas to liquid state. • Many bonds form going from the liquid to the solid state.

• Sublimation - Solid to gas. - Deposition - Gas to solid.

Type of substance Bonds involved in state changes Relative strength Examples of substances • Metals - Metallic Bonds - Strong - Iron, Mercury • Ionic compounds - Ionic Bonds - Strong - Sodium Chloride • Giant covalent structures - Covalent bonds - Strong - Diamond, Silica • Simple molecules - Intermolecular forces - Weak - Oxygen, Water & Wax

• A brittle substance cracks or breaks when an external force is applied. • A malleable substance can change shape without cracking or breaking. • The difference depends on how easily the particles in the substance can change their position in the lattice structure.

• Layers of metal ions slide over one another. - No bonds are broken.

• Giant covalent structure with very many atoms held together in a giant lattice by strong covalent bonds. • Large enough force applied = Many covalent bonds break at once and the substance breaks. • Similar with ionic compounds.

• A substance can conduct electricity if it has charged particles that are free to move. • The delocalised electrons in the structure of the metal are free to move through the structure.

• Ionic compounds contain oppositely charges ions which are free to move when an ionic compound is in the liquid state/molten or dissolves in a solvent such as water. • Ionic compounds can conduct electricity when molten or in solution, but not when they are in the solid state.

• 1nm and 100nm across. • Consist of just a few hundred atoms. • 1nm = 1 x 10-9m.

• A material made from nanoparticles. • Nanoparticulate materials have different properties to the same substance in bulk - E.g. titanium dioxide is white in bulk and transparent when it is nanoparticulate.

• New paints. • New cosmetics, medicines and sunscreens. • Catalysts to speed up industrial chemical reactions. • Self-cleaning windows, ovens and clothes.

Many properties of nanoparticles are due to their very large surface area to volume ratio compared to with the same substance in bulk.

• Nanoparticles are so tiny that they may be breathed in, absorbed by the skin or pass into cells. • May take a long time to break down once released into the environment. • Toxic substances may stick to their surfaces.