The Ancient Greek philosophers believed that there were just four elements: earth, fire, air and water.
An element is a substance made only of one kind of atom.
Out of the 109 known elements, 89 occur naturally on earth.
The rest are made artificially.
A few unreactive elements, such as gold, occur in their pure state; most of the others form compounds with other elements.
It is interesting to note that the human body is made up of hydrogen, oxygen, carbon and nitrogen, while the bones contain calcium. Together, these five elements account for 98% of the body mass. Traces of elements such as copper, zinc and iron occur in our body but these trace elements are very vital for good health.
Most elements are metals. Many of them are found in the Earthís crust, combined with other elements as deposits called ores. Metals in their pure form are either not very strong or they rust of tarnish easily.
The common properties of Metals are:
- Metals have a high melting and boiling point.
- Metals are good conductors of heat and electricity.
- Metals have a high density, and are malleable (can be beaten) and ductile (can be drawn into wire)
- Metals form positive ions.
- Metals react with air to form oxides.
- Metals react with acids to release hydrogen.
- Metals such as aluminum, gallium, indium, thallium, tin, lead, bismuth and polonium are softer and weaker than other metals, and melt more easily.† They are very useful in making alloys.
Most of the metals in use today are in the form of alloys. An alloy is a mixture of different metals or non-metals. Thus, the alloy produced has more useful properties that the metal alone. The new substance alters the atomic structure of the metal so that the metalís atoms do not move. In result a tough and durable material is created.
Boron, silicon, arsenic, germanium, antimony, selenium and tellurium are called semimetals because they have some properties of metals and some of non-metals. Silicon and Germanium are used in the manufacture of electronic components as semi-conductors.
Transition metals form the center block of the periodic table. Some of them are copper, nickel, zinc, iron, silver, platinum etc. They are hard and dense. They are good conductors of heat and electricity. Many of them also act as good catalysts. They often form coloured ions and compounds.† They form alloys with other metals. Some transition metals such as iron, cobalt, and nickel are magnetic.
There are two other groups of metals: alkali metals and alkaline metals. Our bodies do need small amounts of them to stay healthy. They are potassium, calcium, sodium and magnesium.
The alkali metals are: lithium, francium, sodium, potassium, rubidium and caesium. They are soft enough to cut with a knife. They are stored under oil to stop them from reacting with oxygen in the air. Their oxides and hydroxides dissolve in water to give very strong alkaline solutions. They form ions with a single charge. They react with some non-metals to form white, soluble, crystalline salts. They have low melting and boiling points. They have low densities as compared with other metals.
The alkaline metals are beryllium, magnesium, calcium, barium, radium and strontium. They react with water to form alkaline solutions. Their compounds are widely found in nature. They are less reactive than the alkali metals.
The non-metals are phosphorus, sulphur, hydrogen, carbon, nitrogen, oxygen, the halogens (fluorine, chlorine, bromine, iodine and astatine), and the noble gases (helium, neon, argon, krypton, xenon and radon). They are vital to life on Earth.