covalent bonding
Covalent bond is formed when two non-metal elements share their valence electron to reach a full shell of valence electrons. When bonding, two non-metals share their valence electron to reach a full shell of valence electrons.
For example, as you can see from the diagram in the right, it is a Methane (CH4) molecule, you can see the atom of carbon has 4 valence electrons, and hydrogen has only 1, however, if 4 hydrogen atoms each shares an electron to a carbon atom, all of them will have a full shell of valence electron.
intermolecular force
Covalent molecules has weak intermolecular forces, it is because covalent molecules are not usually liquid, gases, or solid with low melting points, which is easy to break them down, however, they have strong bonds between atoms because they need each other's valence electron therefore it is hard to separate the atoms.
sources:
-Covalent bonding. (n.d.). Retrieved December 27, 2016, from http://www.bbc.co.uk/schools/gcsebitesize/science/add_gateway_pre_2011/periodictable/covalentbondingrev1.shtml
-Covalent compounds - simple molecules. Retrieved December 27, 2016, from http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa_pre_2011/atomic/differentsubrev2.shtml