Metals and Non-Metals - Part V

4. Physical and chemical properties of non-metals

Non-Metals display the following physical properties :

1. Non-metals are not malleable or brittle : Non-metals cannot be hammered or beaten into thin sheets without breaking. Non-metals break into pieces when hammered or stretched. Sulphur, phosphorous are powders and cannot be made into a sheet. Brittleness is a characteristic property of non-metals. 

2. Non-metals are not ductile : Non-metals cannot be melted and drawn into thin wires. Non-metals do not have free electrons. Thus the bonds between atoms in the elements are weak and they snap when stretched. The non-ductility property follows from the non-malleability or the brittleness property.

3. Non-metals are bad conductors of heat and electricity : In non-metals, the bonds formed are weak as there are no free electrons to share. Other than graphite, which is an allotropic form of carbon, none of the non-metals are good conductors of heat and electricity. Graphite is able to conduct electricity because of its special crystalline arrangement.

4. Non-metals have no lustre : Non-metals are in the form of powder or are gaseous. Hence they cannot be polished and they do not have any lustre. Most of the powders are dull in colour. Only graphite can be polished to some degree. Iodine shows some lustre as it has more electrons.

5. Non-metals are not strong : Due to their non-ductile and non-malleable properties, non-metals are not strong at all. Their bonds break easily, as the electrons are not shared.

6. Physical state : Non-metals can be in the form of solids, liquids or gaseous at room temperature. Some non-metals like carbon, sulphur, phosphorus are solids at room temperature. Bromine is liquid at room temperature. Most other non-metals are gaseous at room temperature. Solid non-metals are soft materials. Carbon in its allotropic form of diamond is an exception here; diamond is the hardest substance found in nature.

7. Melting and boiling points :  All non-metals, have low melting and boiling points. The melting point of sulphur (S) is 115°C. Graphite and diamonds have high melting points, but these are exceptions in the non-metals.

8. Solubility of non-metals : Non-metals are soluble in some chemical or organic solvents. For example iodine (I) is soluble in alcohol.

9. Density of non-metals : Non-metals have low densities as compared to metals, which have high densities. This means that in non-metals, the atoms are not strongly bound. The crystalline volume of non-metals is small.

10. Non-metals are not sonorous : Non-metals do not make any characteristic sound when hit with an object. Thus non-metals are not sonorous.  

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