Chemical bonding

It has to do with electrons, the ones in the outermost shell, and the need to fill that shell (usually with an octet of electrons) using the least amount of energy.

A good reference is Linus Pauling and his nobel prize winning explanation contained in the theory of the chemical bond.

Rap

H-bonds are critical to human life.

Yeah, yeah, I know the reason why we are all such weaklings. Damn you H-bond.