C2 - Simple Molecular Substances

What are simple molecular substances?

Made up of molecules containing a few atoms joined together by covalent bonds.

What are some common examples of simple molecular substances?

H2 (hydrogen), Cl2 (chlorine), HCl (hydrogen chloride), H2O (water), O2 (oxygen), N2 (nitrogen) and CH4 (methane).

What are some properties of simple molecular substances?

Usually have simple molecular structures, atoms held together by very strong covalent bonds, while intermolecular forces of attraction between molecules are very weak, most are liquids or gases at room temperature as not much energy is needed to overcome the weak intermolecular forces between molecules, as molecules get bigger, melting and boiling points increase as strength of intermolecular forces increase, and they don’t conduct electricity as there are no free electrons or ions.

Why do simple molecular substances have low melting and boiling points?

Although covalent bonds within molecules are very strong, there are weak intermolecular forces of attraction between the different molecules in the substance. Therefore, these forces do not take that much energy to overcome so the molecules are easily parted from each other.