STRUCTURE AND BONDING 61
in the visible part of the spectrum. Thus, for example, in the MnO^
ion, we have manganese in a high oxidation state ( + 7) and oxygen
in state — 2; movement of electrons from oxygen to manganese
requires relatively little energy, and the intense purple colour results.
QUESTIONS
- Discuss the types of bonding that hold atoms and ions together
in molecules and crystals. Include in your answer evidence for the
existence of the bonds that you describe, and some indication of
their relative strength.
(N,A) - Describe, with a brief explanation, the shapes of the following
molecules and ions :
(a) SnCl 2 , (b) BC1 3 , (c) PC1 3 , (d) SbCl 5 , (e) PCl^ and (f) ICI^.
Indicate, giving a reason, which of the molecules (a), (b), (c) and (d)
you would expect to possess a dipole moment.
(JMB, S)- State the type of chemical binding in each of the chlorides
represented by the empirical formulae
NH 4 C1, BeCl 2 , MgCl 2
and show how these binding forces, and other factors, determine the
behaviour of these chlorides when acted upon by (i) heat, (ii) elec-
tricity, (iii) water.
(C,A) - What are the principal differences in physical and chemical
properties between any one metal from Group I and any one metal
from Group IV and any one transition metal? How far can you
explain these differences in terms of their different atomic structures?
(N, Phys. Sc., A) - How can the shapes of simple molecules be explained in terms
of electron pair repulsions? Your answer should include at least one
example from each of four different shapes.
What effect does the presence of a lone pair of electrons on the
nitrogen atom have on :
(a) the H — N — H angle in ammonia,
(b) the properties of the ammonia molecule? (JMB, A)