Oxygen is in Mendeleyev's table in the second period, the main subgroup of the VI group. This chemical element has serial number 8 and atomic mass about 16. Along with sulfur, selenium, tellurium and polonium, it belongs to chalcogens.
Instruction
1. In the nature there are three stable isotopes of oxygen: with atomic numbers 16, 17 and 18, but the first of them prevails. In the form of simple substance – diatomic O2 gas – oxygen is a part of atmospheric air and makes 21% of its volume. In the connected look this chemical element meets as a part of water, minerals and many organic matter.
2. Oxygen is the most widespread element on the planet. It occupies 47.2% of mass of earth crust and makes from 50 to 85% of mass of fabrics of living organisms.
3. Two allotropic modifications of free oxygen – directly O2 oxygen and O3 ozone are known. The last, concentrated in an upper atmosphere, forms the "ozone screen" protecting Earth from harmful ultraviolet rays.
4. Atmospheric O2 oxygen is flavourless colourless gas, it is heavier than air. It has density of 1.43 g/l and boils at a temperature - 183oc. In liter of water only 0.04 g of oxygen are under normal conditions dissolved therefore it treats slightly soluble substances.
5. In the industry oxygen is received fractional distillation of liquid air: in the beginning from it the nitrogen having lower temperature of boiling than at oxygen is driven away, and in the liquid state there is almost pure oxygen. Laboratory methods of receiving oxygen are very extensive, but most often use: decomposition of chlorate of KClO3 potassium, permanganate of KMnO4 potassium, nitrates of alkaline metals (for example, NaNO3), H2O2 hydrogen peroxide. In interaction of peroxides of alkaline metals with carbon dioxide and also at electrolysis of water solutions of alkalis and salts of oxygen-containing acids, oxygen is also emitted. In the latter case process comes down to electric decomposition of water: 2H2O=2H2 ↑+O2 ↑.
6. With other substances oxygen plays an oxidizer role in reactions. Interacting with simple substances, it forms oxides, but at oxidation, for example, sodium and potassium peroxides are formed mainly (Na2O2 and K2O2).
7. Reactions with O2 proceed usually with allocation of energy (ekzotermichna), the exception is made by only endotermichny reaction with nitrogen. Allocation of heat and light is characteristic of the reactions of connection with oxygen called burning. In oxygen many inorganic and organic matter is oxidized (and, in particular, burn).