4) Properties of small molecules

• Simple molecules contain a relatively small number of non-metal atoms joined together by covalent bonds. The molecules have no overall electrical charge, so they cannot conduct electricity.
• Substances that consist of simple molecules usually have low melting and boiling points.

  This is because they have weak intermolecular forces (forces of attraction between the molecules).
• These intermolecular forces are very weak compared to the strength of the covalent bonds in the molecules themselves.
• The larger the molecules are, the stronger the intermolecular forces between the molecules become.
• This means that larger molecules have higher melting and boiling points.
• Going down Group 7 of the periodic table, the molecules get larger and their melting and boiling points increase.
• This is demonstrated by their states at room temperature:

  - Fluorine and chlorine are gases.

  - Bromine is a liquid.

  - lodine is a solid.