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2. Oxygen, the most abundant element on Earth.
present on the Earth as gases (O2, O3, O4),
H2O, and in countless chemical formulas

3. Oxygen composes 21 percent by volume or
23.15 percent by weight of the
atmosphere, 85.8 percent by weight of the
oceans (88.8 percent of pure water is
oxygen), and as a constituent of most rocks
and minerals, 46.7 percent by weight of the
solid crust of the earth.

4. Oxygen comprises 60 percent of the human
body.
It is a constituent of all living tissues, almost
all plants and animals, including all
humans, require oxygen, in the free or
combined state, to maintain life.

5. Three structural forms of oxygen are
known: ordinary oxygen, containing
two atoms per molecule, formula
O2, ozone, containing three atoms per
molecule, formula O3, and a pale
blue, nonmagnetic form, O4, containing
four atoms per molecule, which readily
breaks down into ordinary oxygen.

6. Three stable isotopes of oxygen are
known, oxygen 16 (atomic mass 16) is
the most abundant. It comprises 99.76
percent of ordinary oxygen and was
used in determination of atomic
weights until the 1960s, Oxygen
17(atomic mass 17) and Oxygen 18
(Atomic mass 18).

7. Oxygen supports life
Its normal
concentration in the
air we breathe is
approximately 21 %
We can breathe in a
50-60% oxygen
enriched atmosphere
for several hours
under medical care
(oxygen therapy)

8. Chemical Properties of O2 are:
1-supports combustion.
As the oxygen concentration in air increases, the
potential fire risk increases.
At concentrations above 23 % in air, the situation
becomes dangerous due to the increased fire
hazard.
Because oxygen is colourless, odourless and
tasteless.
by oxygen enrichment can’t be detected by
the normal human senses

9. As we see here The
oxygen doesn’t burn
but supports the
combustion……

10. For a fire or explosion to occur, three elements are required:
Combustible material,
Oxygen
Ignition source
As we know Oxygen doesn’t burn but support
burning…….

11. Oxygen enriched atmosphere can occur at:
Pits, trenches,
Low enclosed areas, underground ways
Sewers
In ASU, cylinder filling plants,…
Around tanker filling
Around vents, leaks
…
In such areas :
o Don’t smoke
o Don’t Use Naked flames
o Don’t weld
o Wear adequate fire-resistant or cotton garments and under clothing.

12. 2-React with Non-metals: Example (Put
quantity of Sulphur powder in Spoon
Ignition then heat it on flame , we notice
Sulphur combustion , and enter the
spoon in a bottleful that includes oxygen
gas, Then we see increasing the
combustion of Sulphur inside the
bottleful , and appearance of foggy
material.....

13. The conclusion of that behavior is: the
increasing of Sulphur combustion in The
Oxygen gas bottleful and forming the foggy
material is an evidence for Sulphur reaction
with Oxygen then forming Sulphur dioxide gas
(SO2)…As below in the equation:
S + O2 SO2

16. 3-React with metals: the Oxygen reacts with
most of metallic elements that yield metallic
oxides..ex: when combustion of Magnesium
ribbon in Oxygen gas, then it will form a white
powder is Magnesium oxide (MgO) , as
below:
2Mg + O2 2MgO
……………..
Another example is shown in photo:

17. 2Mg (s) + O2 (g) 2MgO(s)
4Fe(s) +3O2 (g) 2Fe2O3(s)
4Li(s) + O2(g) 2Li2O (s)
2Cr(s) +3O2(g) 2CrO3(s)
4Cu(s) + O2(g) 2Cu2O(s)

18. The operation of reaction
of oxygen and
elements is called
( Oxidation )…………..