Hinglish

Non-metals and Their Uses

Class 7 Science · Chapter 4: The World of Metals and Non-metals · NCERT Curiosity section 4.4–4.5

Learn

The teacher burns sulfur in a spoon inside a covered jar (in a well-ventilated place: the gas is harmful). Water shaken into the jar dissolves the gas, sulfur dioxide, forming sulfurous acid: it turns blue litmus red. Oxides of non-metals are acidic. Sulfur powder in water does nothing: non-metals generally do not react with water.

sulfur + oxygen → sulfur dioxide (acidic in water)

Sulfur and phosphorus are non-metals: usually soft and dull, neither malleable nor ductile, not sonorous, and poor conductors of heat and electricity. Phosphorus catches fire in air, so it is stored under water. Oxygen, hydrogen, nitrogen and carbon are non-metals too.

Metals and non-metals are elements: substances that cannot be broken into simpler ones (118 are known). Plastic, glass, wood, rubber and paper are not elements, so they are neither metals nor non-metals. Mixtures of metals, or of a metal and a non-metal (like steel: iron and carbon), are alloys.

Non-metals are essential: we breathe oxygen; carbon builds proteins, fats and carbohydrates; nitrogen goes into fertilisers; chlorine purifies water; iodine solution is an antiseptic. India recycles a lot of iron and aluminium, saving resources.

Explore: metal, non-metal or neither?

  1. Sort each one.

Remember

  • Non-metals are dull, brittle, poor conductors and form acidic oxides.
  • Oxygen, carbon, nitrogen, chlorine and iodine are vital non-metals.

Quick check

The oxide of a non-metal dissolved in water is usually …

  1. acidic
  2. basic
  3. neutral
  4. a metal
Answer

acidic. Non-metal oxides are acidic; metal oxides are basic.

Think about it

How do the properties of metals and non-metals decide their uses?

One answer

Metals are strong, malleable, ductile and conduct well, so they make tools, utensils, wires and bridges. Non-metals are poor conductors and many react usefully: oxygen for breathing, chlorine for clean water, nitrogen for fertilisers, carbon for life itself.

Practice

Practise with fresh questions at three levels (easy, medium, hard), some answered hands-on, with hints and worked answers. Get 4 of your last 5 right to finish the topic.