ionic bonding
Ionic bond is formed when metal atoms give electrons to a non-metal atom. When bonding, usually the metal atom gives away electrons to have a full shell of valence electron, and become a positively charged ion, then the non-metal atom gain the electron from the metal to have a full shell of valence electrons, and become a negatively charged ion.
For example, as you can see from the diagram in the right, it is a electron diagram of the molecule NaCl (Salt), where the atom of Sodium gives one electron to chlorine, and sodium becomes a positively charged ion with a +1 charge, and chlorine becomes a negatively charged ion with a -1 charge.
intermolecular force
Ionic compounds have strong intermolecular force, it is because they are attracted by positive and negative ions, just like the north and south in magnet.
sources:
-Ionic bonding. (n.d.). Retrieved December 29, 2016, from http://www.bbc.co.uk/schools/gcsebitesize/science/add_gateway_pre_2011/periodictable/ionicbondingrev1.shtml
-Khan Academy. (n.d.). Retrieved December 29, 2016, from https://www.khanacademy.org/test-prep/mcat/chemical-processes/covalent-bonds/a/intramolecular-and-intermolecular-forces