268 GROUP VI- REACTIONS WITH ELEMENTS
Oxygen is a very reactive element and many metals and non-metals
burn in it to give oxides; these reactions are dealt with under the
individual group headings.
Sulphur is less reactive than oxygen but still quite a reactive
element and when heated it combines directly with the non-metallic
elements, oxygen, hydrogen, the halogens (except iodine), carbon
and phosphorus, and also with many metals to give sulphides.
Selenium and tellurium are less reactive than sulphur but when
heated combine directly with many metals and non-metals.USES OF THE ELEMENTS
OXYGEN
Very large quantities of oxygen are used in steel manufacture (p. 392).
Other important uses include organic oxidation reactions; the
oxidation of ethene CH 2 =CH 2 to epoxyethane, CH 2 —CH 2 , is of
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particular importance. The high temperature flames obtained when
hydrocarbons burn in oxygen have many uses. The oxygen-ethyne
(acetylene) flame, for example, is used in the cutting and welding of
metals. All these products of complete hydrocarbon-oxygen com-
bustion are gases and considerable expansion therefore occurs on
reaction. The thrust produced is the basis of the internal combustion
and many rocket engines.
SULPHUR
Sulphur is used in the manufacture of matches and fireworks, as a
dust insecticide and for vulcanising rubber. Most of the world
supply of sulphur, however, is used for the manufacture of sulphuric
acid (p. 296).
SELENIUM
Like sulphur, selenium has been used in the vulcanisation of rubber.
It is also used in photoelectric cells.