Section 4 - Giant Covalent Substances

Question 1

What is a carbon macromolecule?

Answer 1

A molecule where one carbon atom shares its electrons with four other carbons to gain a full outer shell

Question 2

What are two examples of giant covalent structures that carbon can form?

Answer 2

Diamond and graphite

Question 3

Describe the structure of diamond

Answer 3

Each carbon atom forms four covalent bonds in a very rigid structure. This structure makes diamond very hard.

Question 4

Describe the structure of graphite

Answer 4

Each carbon atom forms three covalent bonds in the sample plane. This results in a series of layers which can slide over each other. The fourth electron from each carbon atom is free.

Question 5

Giant covalent structures - Melting points

Answer 5

Unlike small molecules, melting points are extremely high, as all of the atoms are held together by strong covalent bonds. These millions of covalent bonds need to be broken to allow the atoms within the structure to move freely, which requires a lot of energy. This contrasts with small molecules where no covalent bonds (only intermolecular bonds) need to be broken in order for the substance to melt.

Question 6

Giant covalent structures - Electrical conductivity

Answer 6

Giant covalent structures are electric insulators. This is because they don’t contain charged particles and the atoms aren’t free to move. Even a molten covalent compound will not conduct electricity. Graphite is the only exception to this, as the loosely held electrons between the layers of atoms can move through the solid structure. Graphite conducts in both its solid and liquid forms.

Question 7

Giant covalent structures - Electrical conductivity

Answer 7

Giant covalent structures are electric insulators. This is because they don’t contain charged particles and the atoms aren’t free to move. Even a molten covalent compound will not conduct electricity. Graphite is the only exception to this, as the loosely held electrons between the layers of atoms can move through the solid structure. Graphite conducts in both its solid and liquid forms.

Question 8

Giant covalent structures - Solubility

Answer 8

Giant covalent structures are not soluble in water. To get a giant covalent structure to dissolve, all the covalent bonds joining the atoms together would need to be broken. There is no way to get the energy required to do this, since the individual neutral atoms in the structure will not form intermolecular bonds with the water molecules.