Metals and Non-metals • Topic 1 of 3

Properties of Metals & Non-metals

Elements are broadly divided into metals and non-metals on the basis of their properties. There are about 22 non-metals; the rest are metals. Most metals share a recognisable set of physical and chemical features, but every rule has its exceptions.

Physical properties of metals

  • Lustre: metals have a shining surface (metallic lustre), e.g. gold, silver, copper.
  • Malleability: they can be beaten into thin sheets — gold and silver are the most malleable.
  • Ductility: they can be drawn into thin wires.
  • Conduction: they are good conductors of heat and electricity; silver and copper are the best conductors.
  • Sonorous: they make a ringing sound when struck.
  • They are generally hard, have high density, high melting and boiling points, and are solids at room temperature.

Physical properties of non-metals

Non-metals are usually non-lustrous, brittle (break on hammering), poor conductors and not sonorous. They exist as solids, liquids or gases.

Exceptions you must remember

  • Mercury (Hg) is a liquid metal at room temperature.
  • Sodium (Na) and potassium (K) are so soft they can be cut with a knife.
  • Iodine is a non-metal yet it is lustrous.
  • Graphite (a form of carbon, a non-metal) conducts electricity.
  • Diamond (carbon) is the hardest natural substance and has a very high melting point.

Chemical properties

Reaction with oxygen: metals burn or react with oxygen to form basic oxides, e.g. 2Cu + O2 → 2CuO and 4Al + 3O2 → 2Al2O3. Some metal oxides such as Al2O3 and ZnO are amphoteric — they react with both acids and bases. Non-metals form acidic or neutral oxides, e.g. CO2 and SO2.

Reaction with water: very reactive metals like sodium and potassium react violently with cold water, e.g. 2Na + 2H2O → 2NaOH + H2. Magnesium reacts with hot water; iron reacts only with steam. Non-metals generally do not react with water.

Reaction with acids: metals above hydrogen in the reactivity series displace hydrogen from dilute acids, e.g. Zn + 2HCl → ZnCl2 + H2. Non-metals do not displace hydrogen because they cannot give electrons to H+ ions. Aqua regia (a 3:1 mixture of concentrated HCl and HNO3) is one of the few reagents that can dissolve noble metals like gold and platinum.

Metals vs Non-metals: Physical Properties
PropertyMetalsNon-metals
LustreShiny (except exceptions)Dull (except iodine)
Malleable / ductileYesNo (brittle)
ConductionGoodPoor (except graphite)
SonorousYesNo
State at room tempSolid (except mercury)Solid, liquid or gas
Nature of oxideBasic / amphotericAcidic / neutral
Solved Examples
1
Worked Example
Name a metal that is liquid at room temperature and a non-metal that is lustrous.
Solution
  1. Among metals, mercury (Hg) is the only one that is liquid at room temperature.
  2. Among non-metals, iodine has a shining (lustrous) surface even though it is a non-metal.

Answer: Liquid metal = mercury (Hg); lustrous non-metal = iodine.

2
Worked Example
Why are sodium and potassium stored under kerosene oil?
Solution
  1. Sodium and potassium are extremely reactive metals.
  2. They react vigorously with the oxygen and moisture in air, even catching fire.
  3. Kerosene is inert towards them and keeps out air and water, preventing the reaction.

Answer: They are so reactive with air and moisture (often catching fire) that kerosene is used to keep air and water away.

3
Worked Example
Write the balanced equation for the reaction of sodium with cold water and name the gas evolved.
Solution
  1. Sodium displaces hydrogen from water and forms sodium hydroxide.
  2. Balanced equation: 2Na + 2H2O → 2NaOH + H2.
  3. The gas evolved is hydrogen (H2); the reaction is so exothermic that the hydrogen often catches fire.

Answer: 2Na + 2H2O → 2NaOH + H2; hydrogen gas is evolved.

4
Worked Example
What is meant by an amphoteric oxide? Give one example with equations.
Solution
  1. An amphoteric oxide reacts with both acids and bases to give salt and water.
  2. Example — aluminium oxide with acid: Al2O3 + 6HCl → 2AlCl3 + 3H2O.
  3. With base: Al2O3 + 2NaOH → 2NaAlO2 + H2O.

Answer: An amphoteric oxide (e.g. Al2O3, ZnO) reacts with both acids and bases to form salt and water.

5
Worked Example
What is aqua regia and why is it special?
Solution
  1. Aqua regia is a freshly prepared mixture of concentrated hydrochloric acid and concentrated nitric acid.
  2. The ratio is 3 parts HCl to 1 part HNO3 (3:1).
  3. It is highly corrosive and can dissolve noble metals such as gold and platinum, which ordinary acids cannot.

Answer: Aqua regia is a 3:1 mixture of concentrated HCl and HNO3 that can dissolve gold and platinum.

6
Worked Example
Why do non-metals generally not displace hydrogen from dilute acids?
Solution
  1. Displacing hydrogen from an acid means giving electrons to the H+ ions to form H2.
  2. Non-metals are electron acceptors; they tend to gain electrons rather than lose them.
  3. Since they cannot supply electrons to H+, they do not displace hydrogen from acids.

Answer: Non-metals accept electrons rather than donate them, so they cannot reduce H+ to H2.

Key Points

  • Metals are lustrous, malleable, ductile, sonorous and good conductors; non-metals are usually dull, brittle and poor conductors.
  • Exceptions: mercury is a liquid metal; Na and K are soft; iodine is a lustrous non-metal; graphite conducts; diamond is the hardest substance.
  • Metals form basic oxides (some are amphoteric like Al2O3 and ZnO); non-metals form acidic or neutral oxides.
  • Reactive metals displace hydrogen from dilute acids (Zn + 2HCl -> ZnCl2 + H2); non-metals do not.
  • Aqua regia is a 3:1 mixture of concentrated HCl and HNO3 and can dissolve gold and platinum.
Quick Check — 4 MCQs
Tap an option to check your answer0 / 4
Q1.Which of the following metals is liquid at room temperature?
Explanation: Mercury (Hg) is the only metal that is liquid at room temperature.
Q2.An oxide that reacts with both acids and bases is called:
Explanation: Amphoteric oxides such as Al2O3 and ZnO react with both acids and bases.
Q3.Aqua regia is a mixture of concentrated HCl and HNO3 in the ratio:
Explanation: Aqua regia is 3 parts concentrated HCl to 1 part concentrated HNO3.
Q4.Which non-metal is a good conductor of electricity?
Explanation: Graphite, a form of carbon, conducts electricity due to its free (delocalised) electrons.
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