4.2.2.4 - Properties of small molecules

Give some examples of small / simple molecular substances.

• Hydrogen (H2)

• Chlorine (Cl2)

• Oxygen (o2)

• Nitrogen (N2)

• Methane (CH4)

• Water (H20)

• Hydrogen Chloride (HCl)

Describe the bonds and forces of simple molecular substances.

The atoms within the molecules are held together by very strong covalent bonds, but have weak forces of attraction between the molecules

Do simple molecular substances have high or low melting/boiling points?

Low melting and boiling points - as to change state you only have to overcome the weak forces of attraction between their molecules

What state are most simple molecular substances at room temperature?

Most simple molecular substances are gases or liquids at room temperature

Do simple molecular substances conduct electricity?

No - as they aren’t charged so have no free electrons or ions

When a simple molecular substance melts or boils what is overcome?

The weak intermolecular forces between their molecules (not the covalent bonds)

What do the intermolecular forces increase with?

The intermolecular forces increase with the size of the molecules

So larger molecules have higher melting and boiling points.