There are 22 elements which are non-metals. Of these 11 exist as gas, 10 as solids and only one, i.e., bromine occurs as fluid at room temperature. Some of the important non-metals are nitrogen, oxygen, hydrogen, helium, sulphur, bromine, carbon, neon, etc.
Physical Properties of Non-Metals:
1. Physical State:
Non-metals exist in all the three states, i.e., solid (carbon, phosphorus, and sulphur), liquid (bromine) and gaseous (oxygen, hydrogen, nitrogen).
Most of the non-metals are non-lustrous and dull such as sulphur, phosphorus. Graphite, diamond and iodine crystals are exceptions, as these shine.
3. Soft and Brittle:
The solid non-metals are soft and brittle such as graphite, sulphur and iodine. Only diamond, a form of carbon is hard. In fact, diamond is the hardest substance.
4. Low-density, melting point and boiling point.
Since most of the non-metals are gases at room temperature or are soft, their density is low, and therefore their melting and boiling points are also low. Diamond is an expection as it is hard and its density, melting and boiling points are high. It melts at 350˚C.
5. Non-metals are not malleable or ductile:
Being soft and brittle, non-metals cannot be made into sheets or wires.
6. Bad conductors of electricity and heat:
Non-metals do no possess free electrons to carry charge or heat and hence are poor conductors of electricity and heat. Graphite is the only non-metal which has free electrons in it and is a good conductor of electricity and heat.