Bonding and Structure 4

Question 1

Does boiling point increase or
decrease down the noble gas
group? Why?

Answer 1

Boiling point increases because the
number of electrons increases and
hence the strength of London forces also
increases

Question 2

What conditions are needed
for hydrogen bonding to
occur?

Answer 2

O-H, N-H or F-H bond, lone pair of electrons on O, F, N
Because O, N and F are highly electronegative, H nucleus is left exposed. A strong force of attraction between H nucleus and lone pair of
electrons on O, N, F.

Question 3

Why is ice less dense than

liquid water?

Answer 3

● In ice, the water molecules are arranged in a
orderly pattern. It has an open lattice with
hydrogen bonds.
● In water, the lattice is collapsed and the
molecules are closer together.

Question 4

Why does water have a
melting/ boiling point higher
than expected?

Answer 4

Hydrogen bonds are stronger than other
intermolecular forces so extra strength is
required to overcome the forces

Question 5

What type of intermolecular

forces do alkanes have? Why?

Answer 5

London force → induced dipole-dipole
interaction, because the bonds are
nonpolar

Question 6

What happens to the boiling
point as alkane chain length
increases? Why?

Answer 6

The boiling point increases because there is
more surface area and so more number of
induced dipole- dipole interaction. Therefore
more energy required to overcome the
attraction

Question 7

Does a branched molecule
have lower or higher boiling
point compared to equivalent
straight chain? Why?

Answer 7

The branched molecule has a lower
boiling point because they have fewer
surface area and hence less induced
dipole -dipole interactions.