• Metals & Non-metals. Physical properties of Metals and Non-metals. Description of physical properties of Metals and non-metals.
· There are 118 chemical elements known to be present till May 2011.
· Ununoctium is the latest element discovered in 2002.
· On the basis of their properties all the elements are divided into two main groups:
Occurrence of Elements in Nature
· A large number of elements occur inside or around the earth.
· Less reactive elements, like platinum, gold, nitrogen, oxygen etc., occur in free (native) state.
· Chemically active elements always occur in the combined state i.e. in the form of compounds containing that element. They exist as fluorides, carbonates, chlorides, sulphates, sulphides.
· Metals are lustrous, hard, heavy and sonorous (make a ringing sound when struck).
Characteristics of metals:
· They form positive ions by loosing electrons.
· They are also known as electropositive elements.
· Example-Sodium, copper, silver aluminum etc.they form electropositive ions.
· The most abundant metal in the earth crust is aluminum.
· They are good conductors of heat and electricity.
· They are malleable and ductile.
Characteristics of Non-metals:
· They are generally soft, light substances and non-sonorous.
· They form negative ions by gaining electrons.
· They are also known as electronegative elements.
· Example- carbon, sulphur, oxygen, bromine, iodine.
· They do not conduct heat and electricity.
· They are not malleable and ductile.
· The most abundant non-metal in the earth crust is oxygen.
Physical Properties of Metals
· These are usually solid, except mercury, which is a liquid at room temperature.
· They usually have high density. Iron has density of 7.8 g/cm 3.
· Sodium and potassium have low density (0.97 g/cm 3 and 0.86 g/cm3.
· They usually have a high melting point.
· Iron has melting point of 15350 C.
· Copper has melting point of 10830.
· Gallium has a melting point of 32 DC
· Cesium has melting point of 28 DC
· These metals start melting in hand.
· Their boiling points are usually high.
· They are generally hard, except mercury, sodium, calcium, potassium, lead etc.
· Sodium and potassium are soft metals. They can be easily cut with knife.
Malleability and Ductility:
· The property which allows metals to be converted into thin sheets is called malleability.
· The property which allows metals to be drawn into thin wires is called Ductility.