Hydrogen Bonding
ADVERTISEMENT
1
2C h e m g u i d e – q u e s t i o n s
HYDROGEN BONDING
Important: These questions will also expect you to know about van der Waals forces.
1. The boiling points of the hydrogen halides are:
HF
HCl
HBr
HI
boiling point (K)
293
188
206
238
a) Explain why the boiling points increase from HCl through HBr to HI.
b) The boiling point of HF is far higher than it would be if it fitted the trend in the rest of the group.
That is because hydrogen fluoride can form hydrogen bonds. Using HF as an example, explain
what hydrogen bonds are, and how they arise.
c) Hydrogen bonding is even more effective in water, with the boiling point of water very high for
the size of its molecule. Explain why water can hydrogen bond more effectively than hydrogen
fluoride.
d) Ammonia, NH
, also forms hydrogen bonds, but these have less effect on ammonia's boiling
3
point than is the case with either water or hydrogen fluoride. Can you think of a reason why
hydrogen bonding in ammonia is weaker than in HF?
2. Beryllium chloride, BeCl
, is a covalent compound, which reacts with water to produce a solution
2
containing Be(H
O)
2+
and chloride ions which have water molecules more loosely attached to
2
4
them.
The four water molecules attached to the beryllium ion are joined to it with co-ordinate (dative
covalent) bonds where empty orbitals on the beryllium each accept a lone pair from a water
molecule.
Explain how water molecules become attached to the chloride ions.
3. As well as hydrogen bonding, intermolecular forces include van der Waals dispersion forces and
dipole-dipole interactions.
For each of the following, state which of these forces of attraction occur in the liquid compound.
Don't be scared if you have never heard of some of these! Look at what is in the molecule, and
decide which sort of intermolecular forces might be present.
You may need these electronegativity values:
H: 2.1
C: 2.5
N: 3.0
O: 3.5
F: 4.0
S: 2.5
Cl: 3.0
a) ethanol, CH
CH
OH
3
2
ADVERTISEMENT
0 votes
Related Articles
Related forms
Related Categories
Parent category: Education