7.1-Allotropes of Carbon

Diamond is very hard

• Diamond has a giant covalent structure, made up of carbon atoms that each form four covalent bonds.

  • This makes diamond really hard

• Those strong covalent bonds take a lot of energy to break and give diamonds a very high melting point

• It doesn’t conduct electricity because it has no free electrons or ions

Graphite contains sheets of hexagons

• In graphite, each carbon atom only forms three covalent bonds creating sheets of carbon atoms arranged in hexagons

• There aren’t any covalent bonds between the layers-they’re only held together weakly, so they’re free to move over

  • This makes graphite soft and slippery, so it’s ideal as a lubricating material

• Graphite’s got a high melting point-the covalent bonds in the layers need loads of energy to break

• Only three out of each carbon’s four covalent electrons are used in bonds, so each carbon atom has one electron that’s delocalised(free) and can move

• So graphite conducts electricity and thermal energy

Graphene is one layer of graphite

• Graphene is a sheet of carbon atoms joined together in hexagons

• The sheet is just one atom thick, making it two-dimensional compound

• The network of covalent bonds makes it very strong

  • It’s also incredibly light, so can be added to composite materials to improve their strength without adding much weight

• Like graphite, it contains delocalised electrons so can conduct electricity through the whole structure

  • This means it has the potential to be used in electrons

Fullerenes form sphere and tubes

• Fullerenes are molecules of carbon, shaped like closed tubes or hollow balls

• They’re mainly made up of carbon atoms arranged in hexagons, but can also contain pentagons(rings of five carbon atoms) or heptagons(rings of seven carbon atoms).

• Fullerenes can be used to ‘cage’ other molecules

  • The fullerenes structure forms around another atom or molecule, which is then trapped inside

  • This could be used to deliver a drug into the body

• Fullerenes have a surface area, so they could make great industrial catalysts, individual catalyst molecules could be attached to the fullerenes

7.2-Metallic Bonding

Metallic bonding involves delocalised electrons

• Metals also consist of a giant structure

• The electrons in the outer shell of the metal atoms are delocalised

  • There are strong forces of electrostatic attraction between the positive metal ions and the shared negative electrons

• These forces of attraction hold the atoms together in a regular structure and are known as metallic bonding

  • Metallic bonding is very strong

• Substances that are held together by metallic bonding include metallic elements and alloys

• It’s the delocalised electrons in the metallic bonds which produce all the properties of metals

Most metals are solid at room temperature

• The electrostatic forces between the metal atoms and the delocalised sea of electrons are very strong, so need lots of energy to be broken

• This means that most compounds with metallic bonds have very high melting and boiling points, so they’re generally solid at room temperature

Metals are good conductors of electricity and heat

• The delocalised electrons carry electrical current and thermal energy through the whole structure, so metals are good conductors of electricity and heat

Most metals are malleable

• The layers of atoms in a metal can slide over each other, making metals malleable, this means that they can be bent or hammered or rolled into flat sheets

Alloys are harder than pure metals

• Pure metals often aren’t quite right for certain jobs, they’re often too soft when they’re pure so are mixed with other metals to make them harder

• Most of the metals we use everyday are alloys, a mixture of two or more metals or a metal and another element

  • Alloys are harder and so more useful than pure metals

  • Different elements have different sized atoms, so when another elements is mixed with a pure metal, the new metal will distort the layers of metal atoms, making it more difficult for them to slide over each other