Hazardous Chemicals Handbook (pdf) - CCC

cryogenic conditions (discussed in Chapter 8). The oxygen atom exerts covalent, ionic, or coionic
characteristics. The principle types of compounds are those in which the oxygen atom
• exerts two ionic bonds by accepting two electrons from the same or different atoms, e.g. Ca ++
O – ;
• exerts two covalent bonds by sharing electron pairs, e.g. H 2O;
• exerts co-ionic character by combining with another atom which already has the inert configuration
but of which at least one pair of electrons is unshared, e.g.
Cl
Cl
Cl
P +
O –
Thus oxygen can feature in a wide variety of compounds including ozone, oxides, water,
hydrogen peroxide, carbonates, nitrates/nitrites, etc. It comprises about 21% of normal air (by
volume).
Sulphur molecules are S 8 and it can exist in several forms. Its compounds are more acidic than
those of oxygen and it may assume covalency up to six. It forms a series of oxides and oxyacids
of diverse chemistry. Combustion yields mainly SO 2, a cause of atmospheric pollution from
sulphur-bearing fossil fuels.
Nitrogen, phosphorus, arsenic and antimony
NITROGEN, PHOSPHORUS, ARSENIC AND ANTIMONY 31
None of these elements from Group V form cations of the type N +++++ due to loss of all five
valency electrons. All the elements are strongly electronegative and readily form covalent bonds
with other elements.
Nitrogen is a colourless, tasteless, odourless gas which is slightly soluble in water (see also
page 296). It is non-toxic and inert and comprises about 79% of normal air (by volume). It neither
burns nor supports combustion and at room temperature does not react with any substance. On
heating, however, it combines with oxygen to produce nitric oxide NO, with hydrogen to produce
ammonia NH 3, and with silicon to form silane SiH 4, with calcium carbide to form calcium
cyanamide CaCN 2 and with metals such as lithium, calcium, barium, magnesium and aluminium
to form the corresponding nitrides.
Phosphorus exists as white and red phosphorus. The former allotrope may be preserved in the
dark at low temperatures but otherwise reverts to the more stable red form. The white form is a
waxy, translucent, crystalline, highly-toxic solid subliming at room temperature and inflaming in
air at 35°C, so it is handled under water. The red form is a reddish violet crystalline solid which
vaporizes if heated at atmospheric pressure and condenses to give white phosphorus. The red
form ignites in air at 260°C. Both are insoluble in water, and white phosphorus can be stored
beneath it. Phosphorus forms a host of compounds such as phosphine, tri- and penta-halides,
tri-, tetra- and penta-oxides, oxyacids including hypophosphorous, orthophosphorous and
orthophosphoric acids.
Arsenic exists as grey, yellow and black forms of differing physical properties and susceptibilities
towards atmospheric oxygen. The general chemistry is similar to that of phosphorus but whereas
phosphorus is non-metallic, the common form of arsenic is metallic. Traces of arsenides may be
present in metallic residues and drosses; these may yield highly toxic arsine, AsH 3, with water.
Antimony is a bluish white metal with good lustre but poor heat conducting ability. It is stable
in air and resistant to dilute acids but attacked by halogens, sulphur, phosphorus and arsenic.