Metals and Non-metals
Metals and Non-metals
Metals and non-metals give 2 questions in the Part-III paper. The property table carries most of the marks, and the exceptions carry the rest — because examiners set the exceptions far more often than the rules they break.
Physical Properties
| Property | Metals | Non-metals |
|---|---|---|
| Lustre | Shiny | Dull |
| Malleability | Can be beaten into sheets | Brittle, break on hammering |
| Ductility | Can be drawn into wires | Not ductile |
| Conductivity | Good conductors of heat and electricity | Poor conductors |
| Sonority | Ring when struck | Not sonorous |
| State at room temperature | Mostly solid | Solid, liquid or gas |
The exceptions are the examinable part.
- Mercury is the only metal liquid at room temperature.
- Bromine is the only non-metal liquid at room temperature.
- Sodium and potassium are so soft they can be cut with a knife.
- Graphite, a form of carbon, is a non-metal that conducts electricity.
- Iodine is a non-metal with lustre.
- Diamond, also carbon, is the hardest natural substance.
✗ All non-metals are poor conductors of electricity | ✓ Graphite is a non-metal that conducts electricity well
Chemical Behaviour
The key contrast is in the oxides. Metal oxides are basic and non-metal oxides are acidic. Magnesium burns to give magnesium oxide, which turns red litmus blue; sulphur burns to give sulphur dioxide, which turns blue litmus red.
| Reaction with | Metals | Non-metals |
|---|---|---|
| Oxygen | Basic oxides | Acidic oxides |
| Water | Some release hydrogen | Generally no reaction |
| Dilute acids | Release hydrogen gas | Generally no reaction |
| Bases | Some react | Generally react |
Hydrogen released by a metal and acid is tested with a burning splinter, which burns with a pop sound. That test is asked by name in laboratory questions.
The Reactivity Series
Metals differ in how readily they react. A more reactive metal displaces a less reactive one from its salt solution — the displacement reaction.
Potassium > Sodium > Calcium > Magnesium > Aluminium > Zinc > Iron > Lead > Copper > Silver > Gold
Iron nails placed in copper sulphate solution turn brownish and the blue solution fades, because iron is above copper and displaces it. The reverse does not happen, and questions test exactly that one-way behaviour.
Sodium and potassium react so violently with water that they are stored under kerosene, which is a standard laboratory-safety question. Gold and silver are at the bottom, which is why they are found in native form and do not corrode — the reason they are used in jewellery.
Uses and Corrosion
- Copper and aluminium for electrical wiring, because of conductivity.
- Aluminium foil for wrapping food, because of malleability and non-toxicity.
- Iron for construction, usually as steel.
- Non-metals: oxygen for breathing, nitrogen in fertilisers, chlorine for water treatment, graphite in pencils and electrodes.
Corrosion of iron is rusting; copper develops a green coating and silver blackens. All three are asked together in a matching question, and the green coating on copper is the one candidates miss most often.
धातु के ओक्साइड क्षारीय, अधातु के अम्लीय होते हैं।
TRE pointer: The exceptions are the question. Mercury, bromine, graphite and iodine appear far more often than the general properties they contradict. The metal-oxide-basic and non-metal-oxide-acidic contrast is the most examined chemical point, and the displacement of copper by iron is the standard reactivity question. Sodium stored under kerosene is a safety item a science teacher is expected to know. With −1/3 negative marking, learn the exception list as a block.
60-Second Recap
- Metals are lustrous, malleable, ductile, sonorous and good conductors.
- Mercury is the only liquid metal; bromine the only liquid non-metal.
- Graphite conducts though it is a non-metal; iodine is a lustrous non-metal.
- Metal oxides are basic; non-metal oxides are acidic.
- A more reactive metal displaces a less reactive one from its salt solution.
- Sodium and potassium are stored under kerosene; copper corrodes to a green coating.
Frequently Asked Questions
Which non-metal conducts electricity?
Graphite, which is a form of carbon. It is the standard exception to the rule that non-metals are poor conductors, and it is used in electrodes and in pencil leads for that reason. Diamond, the other form of carbon, does not conduct.
Are metal oxides acidic or basic?
Metal oxides are basic and turn red litmus blue, while non-metal oxides are acidic and turn blue litmus red. Magnesium oxide and sulphur dioxide are the standard examples used to demonstrate this contrast in the class 8 laboratory.
Why are sodium and potassium stored under kerosene?
Because they react violently with the moisture and oxygen in air, and can even catch fire. Kerosene keeps air and water away from the metal surface. This is a laboratory safety point that science teacher recruitment papers ask directly.
What happens when an iron nail is put into copper sulphate solution?
Iron displaces copper, because iron lies above copper in the reactivity series. The blue colour of the solution fades and the nail acquires a brownish copper deposit. The reverse reaction does not occur, and questions test that one-way behaviour.