METALS AND NON-METALS
Lavoiser classified all elements into metals, nonmetals and metalloids on the basis of their properties. Some commonly used metals, nonmetals and metalloids are given below.
(i) Metals : Iron, Copper, Gold, Silver, Aluminium, Zinc, Lead are some commonly used metals.
(ii) Nonmetals : Hydrogen, Oxygen, Nitrogen, Carbon, Sulphur, Phosphorus, Chlorine, Bromine, Iodine are commonly used nonmetals.
(iii) Metalloids : Boron, Silicon, Arsenic and Germanium are some metalloids.
CHARACTERISTICS OF METALS
Some important characteristics of metals are :
(i) Metals are good conductors of heat and electricity.
(ii) All metals except mercury are solid at room temperature. Mercury is the only metal which is liquid at room temperature.
(iii) Metals are malleable and ductile – that is metals can be beaten into thin sheets and drawn into thin wires.
(iv) Metals have lustre and can be polished.
(v) Metals have tensile strength.
(vi) Metals are electropositive elements. That is, metals have a tendency to lose electrons and form positively charged ions, (called cations).
I. Occurrence of Metals
Metals occur in nature in the free as well as in the combined states.
(i) All metals which are not affected by water and by the gases present in the air occur in free state in nature.
(ii) The naturally-occurring compounds of metals mixed with earthly materials are called minerals.
(iii) A mineral from which a metal can be extracted on the commercial scale, economically and easily, is called an ore.
II. Physical Properties of Metals
All metals show similar physical properties. There are however a few exceptions.
(i) Physical State : Under normal pressure, all metals except mercury are solids at room temperature. Mercury is liquid at room temperature.
(ii) Colour : Most metals except gold and copper are silver-grey in colour. Copper is reddish-brown and gold is golden yellow.
(iii) Appearance : All metals are shiny. The characteristic shine of metals is called metallic lustre. Thus all metals have metallic lustre. Metals can be easily polished.
(iv) Hardness : Most metals are hard except sodium and potassium. Sodium and potassium metals can be easily cut with a knife. Osmium is hard enough to scratch glass.
(v) Tensile strength : Metals have high tensile strength. Metals are very strong. For example, iron can bear a lot of stress. That is why it is widely used in construction of buildings, bridges, railway lines &n