Section 4 - Small Covalent Molecules

Question 1

Describe the bonding of small covalent molecules

Answer 1

There are strong covalent bonds between the atoms in each molecule, but very weak intermolecular bonds between the individual molecules. It is these intermolecular bonds that determine the physical properties of small covalent compounds.

Question 2

Small covalent molecules - Melting points

Answer 2

In order to melt (or boil) a small covalent compound, you just have to break the intermolecular bonds between the molecules (not the strong covalent bonds). This doesn’t need much energy, so small molecules normally have very low melting and boiling points - they’re often liquids or gases at room temperature.

Question 3

Small covalent molecules - Electrical conductivity

Answer 3

Small covalent molecule don’t contain any of the free charged particles that are needed to carry an electric charge. As a result they cannot conduct electricity - they’re electrical insulators.

Question 4

Small covalent molecules - Solubility

Answer 4

This varies depending on the type of molecule. Small covalent molecules that are not polar at all (e.g. hydrocarbons) don’t mix well with water, or dissolve very well in it. This is because the attractive force that exists between two water molecules is much stronger than that between a water molecule and a non-polar molecule. Small covalent molecules that are polar or can form hydrogen bonds, can dissolve in water.

Question 5

What are lone pairs in covalent bonding?

Answer 5

Where not all of the electrons of the central atom are bonding electrons

Question 6

Covalent molecules with lone pairs on nitrogen, fluorine or oxygen atoms, bonded to hydrogen (s) can form __________ bonds.

Answer 6

hydrogen

Question 7

Hydrogen bonds are the strongest type of intermolecular bond. What does this mean for its properties?

Answer 7

Substances with hydrogen bonds have high boiling and melting points, and increased solubility