why are hydrogen atoms often associated with molecules that contain oxygen and nitrogen?

Question

king.void. · Answer

http://en.wikipedia.org/wiki/Hydrogen_bond

shrutipande9 · Answer

hydrogen can bond with any atom that either donates or shares electrons...so it not only binds with nitrogen and oxygen but also with many other atoms like chlorine, carbon, sulphur, phosphorus, etc etc

anonymous · Answer

@King.Void. You linked to a article on intermolecular forces.  The question is talking about why hydrogen forms actual bonds (not hydrongen bonding or van der wal forces) with oxygen and nitrogen.

frostbite · Answer

@mrdoldum He did mention the two most abundant high electronegative elements that possess lone pair of electrons in biochemistry. If he said carbon as well then obviously we would be talking about a chemical bond.

So while the covalent bond part has been covered I will go into the hydrogen bonding part:
Hydrogen bounding can be said to take the general form:
A-H•••B
Here are A and B high electronegative elements and B must contain a lone pair. In biochemistry it is conventionally said that only O and N can participate, but F can in principle also participate in hydrogen bonding. The reason why hydrogen bonding so fascinating is due to the strength which can reach about 20 kJ/mol and is virtually like a contact interaction due to the orbital overlap. So as soon the A-H comes in content with B a hydrogen bond is formed and as soon the contact is broken it become zero (not 100% true, but is sufficient to know so far)