Oxygen is the most abundant element on the earth. It makes up 23 percent of air,

89 percent of water, and about 46 percent of crustal rock It also comprises 60 percent of

the human body. Oxygen is an essential element for survival. Without it, we would not be

here today. In this report, you will learn how oxygen, in its many forms, is very important.

Oxygen was first discovered in 1774 by the British chemist Joseph Priestley, when

he decomposed mercury II oxide into its elements by heating it. Karl Wilhelm Scheel, a

Swedish chemist, discovered it when he heated manganese dioxide with concentrated

sulfuric acid.. French chemist, Antoine Laurent Lavoisier, proved it was an elemental gas,

through his experiments on combustion. He also gave oxygen its name. In 1929, W.F.

Giaque and H.L. Johnston announced the discovery of two isotopes of oxygen, with mass

numbers of 17 and 18.

Oxygen is a colorless, odorless, tasteless gas, located in group VIa of the periodic

table. It is slightly denser than air. It is a poor conductor of heat and electricity, and

slightly soluble in water. Oxygen also supports combustion, but does not burn. Its atomic

number is 8. Its atomic mass is 15.9994. Oxygen melts at -218.4 C and boils at -183 C.

It contains 8 protons, electrons, and neurtons. It is also classified as a nonmetal, which

has 2 energy levels. It is also slightly magnetic and not harmful at all. Oxygen can be

condensed to a pale blue liquid, which is very magnetic. It is produced by compressing

the liquid. Oxygen used to be the official standard for the atomic weights of elements.

The chemists used natural oxygen, to which the value of 16 was assigned. In 1961,

however, carbon-12 replaced oxygen as the standard.

There are only three allotropic forms of oxygen known today. There is ordinary

oxygen, which contains two atoms per molecule. Its formula is O2. Ordinary oxygen is

relatively reactive and combines with most elements to form oxides. O2 is required for us

to breathe. Ozone, on the other hand, contains three atoms per molecule. Its formula is

O3. Ozone is formed when oxygen in the air is subjected to an electrical discharge, such

as a bolt of lightning. Ozone is considered a pollutant, because is attacks structural

materials and the tissues of plants and animals. However, it does absorb a great deal of

the ultraviolet radiation from the sun. It is also a colorless gas containing a strong,

irritating odor. There is also O4, which contains four atoms per molecule. It is in a pale

blue, nonmagnetic form, which can be easily broken down into ordinary oxygen.

Oxygen combines with most elements, except the lower-atomic-weight noble

gases, to form oxides. An oxide is a compound formed by the union of oxygen with

another element. Hydrogen combines with oxygen to form hydrogen oxide, also known as

ordinary water. Many oxides occur in nature. Water is the most common one. Carbon

dioxide is also a common oxide in nature.

When oxygen reacts with the metals of Groups I and II, high temperatures are

required to start reactions with the lower-atomic-weight metals, such as lithium, sodium,

potassium, magnesium, and calcium. The higher-atomic-weight metals, like rubidium,

cesium, strontium, and barium, react spontaneously at room temperature. The

electronegativity differences between oxygen and each of these metals is large. The

oxygen compounds formed with them are ionic.

When oxygen reacts with nonmetals, they usually occur at high temperatures of

combustion, because the electronegativity differences between them are small. The oxides

that result from them, contain covalent bonds and exist as molecules. When oxygen reacts

with metals other than those of Groups I and II, they may occur slowly at room

temperature. However, some may react rapidly if the temperature is raised.

When oxygen and certain types of molds and bacteria are present, decay can occur.

Decay is a form of oxidation. Through decay, dead plant and animal materials are

reconverted into carbon dioxide, water, and simple mineral compounds. New generations

of plants and animals now have space to live.

Through the oxygen cycle, oxygen can be used over and over again. When plants

take in carbon dioxide during photosynthesis, water molecules are split and oxygen is

released into the atmosphere. Oxygen is also produced