4. Giant Covalent Lattices

Question 1

What are allotropes? What three carbon allotropes do you need to know about?

Answer 1

different forms of the same element in the same state.
you need to know:
-Graphite
-Diamond
-Graphene.

Question 2

Describe Graphite’s structure.

Answer 2

the carbon atoms are arranged in sheets of flat hexagons covalently bonded with three bonds each. the sheets of hexagons are bonded together by weak induced dipole-dipole forces. the fourth outer electron of each carbon atom is delocalised.

Question 3

Describe graphite’s properties due to its structure.

Answer 3

• weak forces between the layers are easily broken, sheets can slide over each other. it is used as a dry lubricant in pencils as it is slippery.
  -the ‘delocalised’ electrons are free to move along the sheets so an electrical current is able to flow.
  -the strong covalent bond in hexagon sheets give graphite a high melting point.
  -it is insoluble in any solvent due to covalent bonds in the sheets.
  -has a low density due to layers being quite far apart.

Question 4

Describe diamond’s structure.

Answer 4

each carbon atom is covalently bonded to four other carbon atoms. the carbon atoms arrange themselves into a tetrahedral shape- a crystal lattice structure.

Question 5

Describe diamond’s properties due to its structure due to strong covalent bonds.

Answer 5

-has a high melting point.
-extremely hard
-vibrations travel easily through the stiff lattice, good thermal conductor.
-cannot conduct electricity as all outer electrons are held in localised bonds.
-doesn’t dissolve in any solvent.

Question 6

Describe graphene’s structure.

Answer 6

it is a sheet of carbon atoms joined together in hexagons, The sheet is one atom thick making it a two-dimensional compound.
each carbon atom has three covalent bonds and one delocalised electron.

Question 7

Describe graphene’s properties due to its structure.

Answer 7

• the best known electrical conductor due to the delocalised electrons being free to move above and below the sheet quickly
• the delocalised electrons also strengthen the covalent bonds between the carbon atoms.
  -a single layer of graphene is incredibly light and transparent.