Giant Covalent Lattices

Question 1

Giant covalent structures

Answer 1

• Many non-metals form simple molecular lattices that are held by weak intermol. forces.
• Some non-metals like carbon, boron and silicon can form giant covalent lattice with strong covalent bonds.
• Different forms of the same element in same state are called allotropes.

Question 2

Melting and boiling points

Answer 2

High M.P and B.P as covalent bonds are strong.

Question 3

Solubility

Answer 3

Insoluble as covalent bonds are too strong.

Question 4

Graphite

Answer 4

• Parallel layers of hexagonally arranged carbon atoms with 1 delocalised electrons. Layers are bonded by weak London forces.
• Weak London forces are easily broken so sheets can slide over each other so graphite is slippery and used as dry lubricant.
• Delocalised electron allows current flow.
• Layers are far apart so it has low density.
• V high melting points strong covalent bonds.
• Insoluble

Question 5

Diamond

Answer 5

• Each carbon atom is covalently bonded to four other carbon atoms. Atoms arranged in tetrahedral shape.
• V high melting point.
• Extremely hard and used in machine tools.
• Vibrations travel easily through lattice so good conductor.
• Can’t conduct electricity no delocalised electrons
• Insoluble

Question 6

Graphene

Answer 6

• One layer of graphite
• Best known electrical conductor
• V strong as delocalised electrons strengthen covalent bonds
• Transparent v light