4.4 Types of Covalent Structures

Question 1

Giant Covalent Structures (6)

Answer 1

• Giant covalent structures are similar to giant ionic lattices except that there are no charged ions.
• The atoms are bonded to each other by strong covalent bonds.
• No weak intermolecular forces as there is only one structure.
• This means that they have very high melting and boiling points.
• They don’t conduct electricity - not even when molten (except for graphite and graphene).
• They tend to be insoluble in water.

Question 2

Why does chlorine have a low boiling point?

Answer 2

Its intermolecular forces are weaker

Question 3

As you go down the group of halogens, what is the trend?

Answer 3

The molecules are getting bigger, so they’ll be more intermolecular forces between them. This in turn means that more energy will be required to break them all, so the melting and boiling point increases.

Question 4

Why do simple molecular substances not conduct electricity? (2)

Answer 4

• There are no free electrons
• The molecules themselves have no electric charge

Question 5

In silicon dioxide, what ratio of silicon to oxygen are there?

Answer 5

1:2

Question 6

What are the differences between simple molecular substances and giant covalent structures?

Answer 6

• Simple molecular substances are small molecules that are made up of a few covalently bonded atoms, and the separate molecules are only joined together by weak intermolecular forces.
• In giant covalent structures, all of the atoms are covalently bonded in regular repeating lattices. This makes them stronger and have higher melting and boiling points.

Question 7

Diamond, graphite and graphene are __________ of carbon - different forms of the same element.

Answer 7

allotropes

Question 8

Which state do most simple molecular substances exist at in room temperature?

Answer 8

Gaseous state

Question 9

Chorine is a ____ at room temperature.

Answer 9

gas

Question 10

Bromine is a _______ at room temperature.

Answer 10

liquid

Question 11

Iodine is a ______ at room temperature and gives off purple fumes.

Answer 11

solid

Question 12

Simple molecular substances (4)

Answer 12

• Strong covalent bonds between the atoms of each molecule.
• Weak intermolecular forces between molecules.
• Low melting and boiling points (so normally gaseous as room temperature).
• Cannot conduct electricity.