🌬️ Non-metals
Secondary School Chemistry • MalawiHub
1. Introduction
Non-metals are elements that generally do not have the typical physical properties of metals. They are found on the right side of the periodic table, except hydrogen.
Learning Objectives
- Describe physical properties of non-metals.
- Explain important properties of oxygen, hydrogen, nitrogen and sulfur.
- Describe Group 17 halogens.
- Describe Group 18 noble gases.
- Write simple equations involving non-metals.
2. General Properties
- Many are poor conductors of electricity.
- Many have low melting and boiling points.
- They are often brittle when solid.
- They may exist as solids, liquids or gases.
- They usually form acidic or neutral oxides.
Exception: Graphite, a form of carbon, conducts electricity.
3. Oxygen
Oxygen is a colourless gas that supports combustion and is essential for aerobic respiration.
Important properties
- Supports burning.
- Relatively reactive.
- Forms oxides with many elements.
C + O₂ → CO₂
2Mg + O₂ → 2MgO
4. Hydrogen
Hydrogen is a very light, colourless and highly flammable gas.
2H₂ + O₂ → 2H₂O
A mixture of hydrogen and oxygen can be explosive when ignited.
5. Nitrogen
Nitrogen makes up most of Earth's atmosphere. It is relatively unreactive because the nitrogen molecules contain a strong triple bond.
Nitrogen is important in the manufacture of ammonia and fertilisers.
6. Carbon
Carbon exists in different forms called allotropes.
| Allotrope | Important property |
|---|---|
| Diamond | Very hard and does not conduct electricity. |
| Graphite | Soft and conducts electricity. |
| Graphene | Very thin carbon layers with useful electrical properties. |
7. Sulfur
Sulfur is a yellow solid non-metal. It burns in oxygen to form sulfur dioxide.
Sulfur dioxide can contribute to acid rain and must be controlled in industrial emissions.
8. Halogens — Group 17
Halogens are reactive non-metals found in Group 17.
| Element | State at room temperature |
|---|---|
| Fluorine | Gas |
| Chlorine | Gas |
| Bromine | Liquid |
| Iodine | Solid |
Halogen reactivity generally decreases down the group.
Cl₂ + 2KBr → 2KCl + Br₂
9. Noble Gases — Group 18
Noble gases are very unreactive because they have stable outer electron arrangements.
| Gas | Example use |
|---|---|
| Helium | Balloons |
| Neon | Advertising signs |
| Argon | Light bulbs and welding |
10. Non-metal Oxides
Many non-metal oxides are acidic.
Carbon dioxide dissolving in water forms carbonic acid.
11. MANEB Examination Focus
- Compare metals and non-metals.
- Describe important non-metals.
- Explain halogen displacement reactions.
- Explain the low reactivity of noble gases.
- Describe carbon allotropes.
- Write equations involving oxygen and sulfur.
Chlorine is added to potassium bromide solution. Predict the products and explain your answer.
Cl₂ + 2KBr → 2KCl + Br₂.
Chlorine is more reactive than bromine, so it displaces bromine from potassium bromide.
12. Practice Exercises
- State two general properties of non-metals.
- What gas supports combustion?
- Write the equation for hydrogen burning in oxygen.
- Why is nitrogen relatively unreactive?
- Name two allotropes of carbon.
- What happens to halogen reactivity down Group 17?
- Why are noble gases unreactive?
Answers
- Generally poor electrical conductors and often brittle when solid.
- Oxygen.
- 2H₂ + O₂ → 2H₂O.
- It contains a strong N≡N triple bond.
- Diamond and graphite.
- It generally decreases.
- They have stable outer electron arrangements.
13. Common Mistakes
- Do not say all non-metals are gases.
- Remember that graphite conducts electricity.
- Do not confuse halogens with noble gases.
- Check the reactivity order before predicting displacement.
14. Exam Tip
For Group 17 displacement questions, a more reactive halogen displaces a less reactive halide from solution.