Oxygen, the most abundant element on Earth.

present on the Earth as gases (O2, O3, O4),

H2O, and in countless chemical formulas

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.

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.

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.

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).

Oxygen supports lifeIts 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)

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

As we see here The

oxygen doesn’t burn

but supports the

combustion……

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…….

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.

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.....

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

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:

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)

The operation of reaction

of oxygen and

elements is called

( Oxidation )…………..