1. INTERMOLECULAR BONDS
1. Arrange the following substances in increasing order of strength of inter-particle forces at room
temperature and pressure: neon, sulphur, mercury.
ANSWER: Neon, mercury, sulphur
2. Name the major inter-unit forces in solid KOH
ANSWER: Electrostatic / ionic bond
3. Name the major inter-unit forces in liquid 2-butanone.
ANSWER: Dipole – dipole.
1. Why do network covalent solids have higher melting point than molecular solids?
Ans: Molecular solids consist of discrete molecules held together by weak
intermolecular forces. Melting only breaks down these weak forces. Network
covalent solids are giant molecules whose atoms are held by strong covalent
bonds. Melting involves either breaking the strong covalent bonds or
providing enough average kinetic energy to the very heavy molecules.
ROUND 1
1. Which of these compounds will not show hydrogen bonding in the liquid state; give
you reason(s). (BH3)2, MeNH2, HF, H2S and HCHO
Ans: (BH3)2, H2S and HCHO. In all the three compounds, hydrogen is not
bonded to a very electronegative atom.
2. Ethanoic acid shows a special kind of intermolecular hydrogen bonding. Describe it
and give the outcome of this bonding
Ans: There is hydrogen bonding between pairs of the molecules to give dimers. H
of OH on one to C=O of the other molecule and vice versa.
3. There is extensive hydrogen bonding in liquid water. Give two properties of water due
solely to the strong hydrogen bonding.
Ans: (1) Higher boiling point than H2S
(2) High surface tension
(3) Water expanding when it freezes.
1. What is the general name given to forces of attraction between covalent molecules?
ANSWER: van der Waal’s forces
2. Which is the strongest of the van der Waal’s forces?
2. ANSWER: Hydrogen bonds
3. What kind of intra-molecular forces exist between carbon II oxide molecules?
4. Explain why H2O has a higher boiling point than H2S despite the fact that the former has
a lower molar mass
ANSWER: Extensive and strong H-bonding in H2O but none in H2S
5. Explain why water expands when it freezes.
ANSWER: The strong H-bonding in water molecules prevents the water
molecules from packing close to one another.
ANSWER: Dipole-dipole
1. If the dipole moment of carbon II oxide molecule is 0.10 Debye, what could be the value
for carbon IV oxide?
ANSWER: Zero the dipoles cancel out
2. If the dipole moment for CHCl3 molecule is 1.02 Debye, what could be the value for CCl4
molecule?
ANSWER: Zero Symmetrical molecules, the 4 dipoles cancel out.
3. The dipole moment for CO2 molecule is zero while that for SO2 is 1.64 Debye. What
could account for this difference?
ANSWER: CO2 is linear hence dipoles cancel out, SO2 is a bent molecule,
dipoles do not cancel out.
1. How many covalent bonds are present in the ClO3
-
ion?
ANSWER: 6
2. How many covalent bonds are present in the HNO3 molecule?
ANSWER: 6
3. How many covalent bonds are in the molecule of phosgene, COCl2, a highly poisonous
gas?
ANSWER: 4
1. State the molecular forces that are present in pure ethanoic acid liquid.
ANSWER: Inter-molecular hydrogen bonding.
2. State the molecular forces present in liquid propanone.
ANSWER: Dipole – dipole (No Hydrogen bonding because there is no H bonded to an
electronegative atom in the molecule).
3. 3. Explain why CO2 is less polar than SO2.
ANSWER: SO2 is bent and the dipoles do not cancel out. CO2 is linear and the dipoles
cancel out.
