keemiliste elementide perioodilisussüsteemi VI rühma element, sümbol O (oxygenium)
colourless odourless gaseous element belonging to group 16 (formerly VIB) of the periodic table; a.n. 8; r.a.m. 15.9994; d. 1.429 g dm−3; m.p. –218.4°C; b.p. –183°C
Hea teada
It is the most abundant element in the earth’s crust (49.2% by weight) and is present in the atmosphere (28% by volume). ... The common form is diatomic (dioxygen, O2); there is also a reactive allotrope ozone (O3). Chemically, oxygen reacts with most other elements forming oxides.
Nii maakoores kui elavates organismides leidub hapnikku kõigist elementidest kõige rohkem. Hapnikku esineb looduses mitme allotroopse teisendina. Lisaks tavalisele hapnikule ehk dihapnikule on olemas ka trihapnik ehk osoon.
During respiration, animals and some bacteria take oxygen from the atmosphere and return to it carbon dioxide, whereas by photosynthesis, green plants assimilate carbon dioxide in the presence of sunlight and evolve free oxygen.
