OXYGEN OCCURRENCE

· Oxygen is the most abundant element in the Earth's crust. The atmospheric air contains this element in a free state, while water, minerals, rock, and all the substances building the organisms of plants and animals contain oxygen in a combined state.

· The total amount of oxygen in the Earth's crust is close to half of its total mass (47%).

· Dioxygen comprises about 21% (by volume) of the Earth’s atmosphere.

· Natural oxygen consists of three stable isotopes: ¹⁶0 (99.76 %), ¹⁷O (0.04%), and ¹⁸O (0.2%).

• Oxygen of air is consumed in burning, breathing, rotting, corroding processes and it is continuously regenerated due to photosynthesis (formation of carbohydrates and oxygen):

nCO₂ + mH₂O ® C_n(H₂O)_m + nO₂.

• Essential for life. To satisfy the demands of living creatures for oxygen its partial pressure in air is important. Despite that the percentage of oxygen gas in mid air remains without changes, its partial pressure on considerable heights becomes insufficient for breathing as a result of atmosphere thinning. For this reason at climbing to the tops of mountains or in heigh flights the human body suffers oxygen starvation.

· Н₂О is the most important compound of oxygen on Earth. Water occupies the greater part of the Earth surface, being in 3 aggregate states. Its enormous masses are contained in the minerals and mountain rocks. The organism of a man contains about 60% of water. Quantitively a man weighing 70 kg contains approximately 1750 mol of oxygen as water and organic compounds.

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Chemical properties of oxygen

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