What are the strongest intermolecular forces in CH4, NH3 and H2O? From this deduce which has the highest boiling point, giving reasoning.

The cental atom in each of these molecules is C, N and O respectivly, of these both N and O are members of the family of three atoms that can form hydrogen bond (also incluidng F), when directly bonded to hydrogen. Due to this the strongest intermolecular forces between NH3 and H2O are hydrogen bonds. C is not electronegative enough to form hydrogen bonds, due to it having a larger atomic radius than both N and O. Also CH4 molecules cannot have permenant dipole-dipole attractions because each of the species bonded to the carbon is identical and CH4 has a tetrahedral shape. Therefore the strongest intermolecular forces between CH4 molecules are Van der Waals forces.

Hydrogen bond are stronger than Van der Waals forces therefore both NH3 and H2O will have higher boiling points than CH4. O has a smaller atomic radius than N, as O has a more positive nucleus, but the valance electrons in both N and O are in the same princible energy level (2p). As a result of this O is more electronegative so has a greater ability to draw electrons in a covalent bond, becoming more δ- than N, leaving the surrounding hydrogen atoms more available to form hydrogen bonds, so H2O has the highest boiling point.