Physical properties of Non-metals

In the previous Class you have learnt that there are very few non-metals as compared to metals. Some of the examples of non-metals are carbon, sulphur, iodine, oxygen, hydrogen, etc. The non-metals are either solids or gases except bromine which is a liquid.

Do non-metals also have physical properties similar to that of metals? Let us find out.

Activity 3.7

1. Collect samples of carbon (coal or graphite), sulphur and iodine.
2. Carry out the Activities 3.1 to 3.6 with these non-metals and record your observations.

Compile your observations regarding metals and non-metals in Table 3.1.

On the bases of the observations recorded in Table 3.1, discuss the general physical properties of metals and non-metals in the class. You must have concluded that we cannot group elements according to their physical properties alone, as there are many exceptions. For example –

(i) All metals except mercury exist as solids at room temperature. In Activity 3.5, you have observed that metals have high melting points but gallium and caesium have very low melting points. These two metals will melt if you keep them on your palm.

(ii) Iodine is a non-metal but it is lustrous.

(iii) Carbon is a non-metal that can exist in different forms. Each form is called an allotrope. Diamond, an allotrope of carbon, is the hardest natural substance known and has a very high melting and boiling point. Graphite, another allotrope of carbon, is a conductor of electricity.

(iv) Alkali metals (lithium, sodium, potassium) are so soft that they can be cut with a knife. They have low densities and low melting points.

Elements can be more clearly classified as metals and non-metals on the basis of their chemical properties.

Activity 3.8

1. Take a magnesium ribbon and some sulphur powder.
2. Burn the magnesium ribbon. Collect the ashes formed and dissolve them in water.
3. Test the resultant solution with both red and blue litmus paper.
4. Is the product formed on burning magnesium acidic or basic?
5. Now burn sulphur powder. Place a test tube over the burning sulphur to collect the fumes produced.
6. Add some water to the above test tube and shake.
7. Test this solution with blue and red litmus paper.
8. Is the product formed on burning sulphur acidic or basic?
9. Can you write equations for these reactions?

Most non-metals produce acidic oxides when dissolve in water. On the other hand, most metals, give rise to basic oxides. You will be learning more about these metal oxides in the next section.