Question

If a solid line represents a covalent bond and a dotted line represents intermolecular attraction, which of the choices shows a hydrogen bond? OH,N.....H-0-H H.C......H-F D H,0.....H-CH, Он-Н

Answer 1

A hydrogen bond is a weak bond between two molecules which arises from an electrostatic attraction between a proton (bonded to strongly electronegative atom) in one molecule and an electronegative atom in the other (having a lone of electrons) . The presense of lone pair on the electronegative atom is necessary and hence second-row elements like nitrogen, oxygen and fluorine shows H-bond. These conditions are important for formation of H-bond.

Let us see the options now-

1) You can clearly see that here there is a bond between electronegative atom Nitrogen of ammonia and proton of water. So it is a hydrogen bond.

2) Here carbon of methane is not an electronegative atom. So this is not H-bond.

3)You may think that this is a hydrogen bond as proton is bonded to an electronegative atom oxygen. But that is not the case. You can see that proton is covalently bonded to carbon which is not electronegative. For hydrogen bond formation both the atoms to which proton is bonded has to be electronegative.

4) The bond in Hydrogen molecule is a covalent bond and not a hydrogen bond.

So, correct option is option 1.