11 Group VII: the halogens
(Fluorine, chlorine, bromine, iodine)PHYSICAL PROPERTIES
Table 1L1 and Table 11.2 (p. 314) give some of the physical proper-
ties of the common halogens. Figure 11.1 shows graphically some
of the properties given in Table 11.1, together with enthalpies of
atomisation.
It can be seen that many properties change regularly with in-
creasing atomic number, the changes being approximately linear in
the case of the three elements chlorine, bromine and iodine, but a
discontinuity almost always occurs for fluorine. This behaviour is
typical for a group head element, which in addition tends to display
properties not shown by other members of the group; a greater
disparity in properties occurs between the first and second elements
in a group than between any other two adjacent group elements.
OXIDATION STATES
The electronic configuration of each halogen is one electron less
than that of a noble gas, and it is not surprising therefore, that all
the halogens can accept electrons to form X~ ions. Indeed, the
reactions X(g) 4- e~ -» X~(g\ are all exothermic and the values
(see Table 11.1), though small relative to the ionisation energies, are
all larger than the electron affinity of any other atom.
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