GROUP V 255
differences. Show how the increasing metallic character of the element
is reflected in the chemical behaviour of these compounds. Suggest a
reason for the non-existence of AsCl 5 and BiQ 5.
(C,S)- Outline the laboratory preparation of a sample of dinitrogen
tetroxide. Describe and explain what happens when it is heated from
290 K to 900 K. Suggest electronic structures for dinitrogen tetroxide
and the other nitrogen-containing molecules formed from it on
heating to 900 K. Point out any unusual structural features.
(C,A) - For either Group IV or Group V:
(a) point out two general trends in the physical properties of the
elements, and explain, as far as you can, why these trends
occur;
(b) give examples of the way in which the most stable oxidation
number of the elements in their compounds tends to decrease
by two towards the bottom of the group, and describe how
this tendency is related to their oxidising and reducing
properties:
(c) describe in outline how, starting from the element, you would
prepare a pure sample of either an oxide or chloride of an
element in the group, and state how you would, in principle,
try to establish its empirical formula.
(N, Phys. Sci. A) - Compare and contrast the following pairs of compounds as
regards (a) methods of preparation, (b) important properties includ-
ing hydrolysis, (c) thermal stability:
(i) NCl 3 andPCl 3 ;
(ii) NH 3 andPH 3 ;
(iii)N 2 O 5 andP 4 O 10.As far as possible account for different behaviour in terms of the
structures of the compounds and the nature of bonding present.
(L,S)
- (a) What is meant by the statement that 'nitrogen dioxide,
NO 2 , is an odd-electron molecule'?
(b)When NO 2 dimerises to form N 2 O 4 , the product is not an
odd-electron molecule. What explanation can you offer for this
fact?