The World of Metals and Non-metals

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CLASS VII Science ~6 marks/year Ch 4 of 12
The World of Metals and Non-metals

Class 7 · Science · NCERT chapter notes · Akanksha Classes

Snapshot
  • Elements are classified into metals and non-metals based on their physical and chemical properties.
  • Metals are usually hard, shiny (lustrous), malleable, ductile, sonorous and are good conductors of heat and electricity (e.g. iron, copper, aluminium, gold).
  • Non-metals are usually dull, soft (or brittle if solid), non-malleable and are poor conductors (e.g. sulphur, carbon, oxygen). They may be solids, liquids or gases.
  • Malleability = can be beaten into thin sheets; ductility = can be drawn into wires; sonority = produces a ringing sound when struck.
  • Metals react with oxygen to form basic oxides; non-metals react with oxygen to form acidic oxides.
  • Some metals react with water and with acids to release hydrogen gas; reactivity differs from metal to metal.
  • There are a few exceptions — mercury is a liquid metal, carbon (graphite) conducts electricity, and iodine is a lustrous non-metal.
  • Weightage: ~6 marks/year — property comparison, malleable/ductile terms, reactions and uses of metals/non-metals.
Detailed Notes

1. Materials Around Us: Metals and Non-metals

The things around us are made of different materials. Many elements can be sorted into two big groups: metals and non-metals. Iron, copper, aluminium, gold and silver are metals. Carbon, sulphur, oxygen and hydrogen are non-metals. The two groups behave very differently, and we tell them apart by studying their properties.

Metals are elements that are usually hard, shiny, malleable, ductile, sonorous and good conductors of heat and electricity. Non-metals are elements that usually lack these metallic properties.

2. Physical Properties of Metals

Metals share several characteristic physical properties.

2.1 Metallic lustre (shine)

Metals have a shiny appearance called metallic lustre. A freshly cut or polished piece of metal shines. Gold and silver are valued partly for their lustre.

2.2 Hardness

Most metals are hard (e.g. iron). However, some metals like sodium and potassium are so soft that they can be cut with a knife — these are exceptions.

2.3 Malleability

Malleability: the property of metals to be beaten into thin sheets without breaking. Gold and aluminium are highly malleable (used as foils).

2.4 Ductility

Ductility: the property of metals to be drawn into thin wires. Copper and aluminium are ductile and are used to make electric wires.

2.5 Good conductors of heat and electricity

Metals allow heat and electric current to pass through them easily. That is why cooking utensils are made of metals and electric wires are made of copper or aluminium.

2.6 Sonority

Sonority: metals produce a ringing sound when struck. School bells and temple bells are made of metal because they are sonorous.

2.7 High melting and boiling points; high density

Most metals have high melting and boiling points and are generally dense (heavy for their size). Metals are usually solids at room temperature.

NCERT activity — Testing malleability and sonority

Take a metal object (an iron nail or a piece of aluminium) and a non-metal (a piece of coal/charcoal). Place each on a hard surface and tap gently with a hammer. The metal flattens a little and may give a ringing sound (malleable and sonorous). The coal breaks into pieces with a dull sound (brittle and not sonorous). This shows that metals are malleable and sonorous, while non-metals are not.

3. Physical Properties of Non-metals

Non-metals generally show the opposite properties to metals.

  • Appearance: usually dull (no lustre). Exception: iodine and graphite are lustrous.
  • State: can be solids (sulphur, carbon), liquids (bromine) or gases (oxygen, nitrogen).
  • Hardness: solid non-metals are usually soft or brittle (break easily). Exception: diamond (a form of carbon) is the hardest natural substance.
  • Not malleable, not ductile: they cannot be beaten into sheets or drawn into wires; they break.
  • Poor conductors: non-metals are bad conductors of heat and electricity. Exception: graphite conducts electricity.
  • Not sonorous: they do not produce a ringing sound.

3.1 Comparison table: metals vs non-metals

Property Metals Non-metals
LustreShiny (lustrous)Dull (mostly)
MalleabilityMalleableNot malleable (brittle)
DuctilityDuctileNot ductile
ConductionGood conductorPoor conductor
SonoritySonorousNot sonorous
State at room temp.Mostly solidsSolids, liquids or gases

4. Chemical Properties — Reaction with Oxygen

Metals and non-metals also differ in how they react chemically.

4.1 Metals react with oxygen to form basic oxides

When metals burn or react with oxygen, they form metal oxides. Metal oxides are basic in nature — those that dissolve in water turn red litmus blue.

Metal + Oxygen → Metal oxide (basic). Example: when magnesium burns, magnesium oxide (MgO) is formed; its solution turns red litmus blue.

For example, iron reacts slowly with oxygen and moisture to form a reddish-brown coating of rust (iron oxide). Burning magnesium ribbon gives a bright white light and white magnesium oxide powder.

4.2 Non-metals react with oxygen to form acidic oxides

Non-metals react with oxygen to form non-metal oxides, which are usually acidic — their solutions turn blue litmus red.

Non-metal + Oxygen → Non-metal oxide (acidic). Example: carbon burns in oxygen to form carbon dioxide (CO2); when dissolved in water it forms carbonic acid, turning blue litmus red.

Sulphur burns in air to form sulphur dioxide (SO2), which also makes an acidic solution. Such acidic oxides released by burning fuels contribute to acid rain.

NCERT activity — Nature of metal and non-metal oxides

Burn a small piece of magnesium ribbon (with care) and collect the white ash in a test tube; add a little water and test with litmus — it turns red litmus blue, showing the oxide is basic. Separately, burn a little sulphur, collect the gas in water and test — it turns blue litmus red, showing the oxide is acidic. This shows metal oxides are basic and non-metal oxides are acidic.

5. Reaction with Water

Different metals react with water to different extents, releasing hydrogen gas.

  • Very reactive metals (sodium, potassium) react vigorously even with cold water, producing hydrogen and catching fire — so they are stored in kerosene.
  • Some metals (like iron) react slowly with water and moist air, forming rust over time.
  • Less reactive metals (gold, silver) do not react with water.

Most non-metals do not react with water at all.

Metal + Water → Metal hydroxide/oxide + Hydrogen gas (for reactive metals). Sodium and potassium are stored in kerosene because they react violently with water and air.

6. Reaction with Acids

Most metals react with dilute acids to produce a salt and hydrogen gas. The hydrogen gas is the gas that escapes as bubbles.

Metal + Dilute acid → Salt + Hydrogen gas. The hydrogen burns with a "pop" sound when a lighted matchstick is brought near it — this is the test for hydrogen.

For example, zinc reacts with dilute hydrochloric acid to give zinc chloride and hydrogen gas. Non-metals generally do not react with dilute acids to release hydrogen.

NCERT activity — Test for hydrogen gas

Put a few pieces of zinc granules in a test tube and add some dilute hydrochloric acid. You will see bubbles of gas. Bring a burning matchstick near the mouth of the test tube — the gas burns with a "pop" sound. This pop test confirms that the gas released is hydrogen, produced when a metal reacts with an acid.

7. Exceptions to Remember

Some elements do not follow the usual rules, and these exceptions are often asked in exams.

  • Mercury — a metal that is liquid at room temperature.
  • Sodium and potassium — metals that are very soft (can be cut with a knife).
  • Graphite (a form of carbon) — a non-metal that conducts electricity.
  • Iodine — a non-metal that is lustrous (shiny).
  • Diamond (a form of carbon) — a non-metal that is the hardest natural substance.
Key exceptions: mercury (liquid metal), graphite (conducting non-metal), iodine (shiny non-metal), diamond (hardest non-metal), sodium/potassium (soft metals).

8. Uses of Metals and Non-metals

8.1 Uses of metals

  • Iron and steel: buildings, bridges, machines, vehicles, tools.
  • Copper and aluminium: electrical wires and cooking utensils (good conductors).
  • Gold and silver: jewellery and coins (lustrous, do not corrode easily).
  • Aluminium: foils, cans, aircraft bodies (light and malleable).

8.2 Uses of non-metals

  • Oxygen: needed for breathing (respiration) and for burning fuels.
  • Nitrogen and phosphorus: used in fertilisers for plant growth.
  • Carbon: graphite in pencils and as electrodes; diamond for cutting tools.
  • Iodine: as an antiseptic (iodine tincture) for wounds.
  • Sulphur: used in medicines, crackers and to make sulphuric acid.
Practice MCQs
1. The property of metals to be beaten into thin sheets is called:
  1. Ductility
  2. Malleability
  3. Sonority
  4. Lustre
Answer: (B) Malleability is the ability to be beaten into thin sheets, like gold and aluminium foil.
2. The property of metals to be drawn into thin wires is called:
  1. Malleability
  2. Ductility
  3. Hardness
  4. Sonority
Answer: (B) Ductility is the ability to be drawn into wires; copper and aluminium are ductile.
3. Which of these is a good conductor of electricity?
  1. Sulphur
  2. Copper
  3. Wood
  4. Plastic
Answer: (B) Copper is a metal and a good conductor of electricity. Sulphur, wood and plastic are poor conductors.
4. The ringing sound produced by metals when struck is due to the property called:
  1. Malleability
  2. Ductility
  3. Sonority
  4. Density
Answer: (C) Sonority is the property of producing a ringing sound; bells are made of sonorous metals.
5. Which metal is a liquid at room temperature?
  1. Iron
  2. Mercury
  3. Copper
  4. Gold
Answer: (B) Mercury is the only common metal that is liquid at room temperature.
6. Which non-metal is a good conductor of electricity?
  1. Sulphur
  2. Oxygen
  3. Graphite (carbon)
  4. Iodine
Answer: (C) Graphite, a form of carbon, is a non-metal that conducts electricity — an exception.
7. Metal oxides are generally:
  1. Acidic
  2. Basic
  3. Neutral
  4. Always gases
Answer: (B) Metals react with oxygen to form basic oxides, which turn red litmus blue.
8. When carbon burns in oxygen, the oxide formed (carbon dioxide) is:
  1. Basic
  2. Acidic
  3. Neutral
  4. Metallic
Answer: (B) Non-metal oxides like CO2 are acidic; dissolved in water they turn blue litmus red.
9. Sodium and potassium are stored in kerosene because they:
  1. Are very expensive
  2. React violently with water and air
  3. Are gases
  4. Do not react at all
Answer: (B) These very reactive metals react vigorously with water and air, so they are kept in kerosene for safety.
10. When a metal reacts with a dilute acid, the gas released is:
  1. Oxygen
  2. Carbon dioxide
  3. Hydrogen
  4. Nitrogen
Answer: (C) Metal + dilute acid → salt + hydrogen gas, which burns with a "pop" sound.
11. The "pop" sound test is used to identify which gas?
  1. Oxygen
  2. Hydrogen
  3. Carbon dioxide
  4. Sulphur dioxide
Answer: (B) Hydrogen burns with a characteristic "pop" sound when a burning matchstick is brought near it.
12. Which of the following is a non-metal that is lustrous (shiny)?
  1. Sulphur
  2. Carbon (coal)
  3. Iodine
  4. Oxygen
Answer: (C) Iodine is a non-metal but has a shiny (lustrous) appearance — an exception.
13. Electric wires are made of copper or aluminium mainly because these metals are:
  1. Brittle and dull
  2. Ductile and good conductors
  3. Sonorous and heavy
  4. Liquid at room temperature
Answer: (B) Copper and aluminium are ductile (can be drawn into wires) and are good conductors of electricity.
14. The hardest naturally occurring substance, which is a form of carbon, is:
  1. Graphite
  2. Diamond
  3. Sulphur
  4. Iron
Answer: (B) Diamond, a form of carbon (a non-metal), is the hardest natural substance — an exception.
15. Which set lists only non-metals?
  1. Iron, copper, gold
  2. Oxygen, sulphur, carbon
  3. Aluminium, silver, zinc
  4. Mercury, iron, lead
Answer: (B) Oxygen, sulphur and carbon are all non-metals. The other sets contain metals.
Important Questions
Q1. Define malleability and ductility. Give one example of a use of each. (2 marks)
Answer: Malleability is the property of metals to be beaten into thin sheets without breaking; for example, aluminium is rolled into foil used for wrapping food. Ductility is the property of metals to be drawn into thin wires; for example, copper is drawn into wires used for carrying electricity.
Q2. Write any four differences between metals and non-metals. (3 marks)
Answer: (1) Metals are lustrous (shiny); non-metals are usually dull. (2) Metals are malleable and ductile; non-metals are brittle and cannot be beaten or drawn into wires. (3) Metals are good conductors of heat and electricity; non-metals are poor conductors. (4) Metals are sonorous (produce a ringing sound); non-metals are not. (Also: metals form basic oxides, non-metals form acidic oxides.)
Q3. What type of oxides do metals and non-metals form? How can you test their nature with litmus? (2 marks)
Answer: Metals react with oxygen to form basic oxides, while non-metals form acidic oxides. To test: dissolve the oxide in water and test with litmus. A metal oxide solution turns red litmus blue (basic). A non-metal oxide solution turns blue litmus red (acidic).
Q4. Why are sodium and potassium stored in kerosene? (2 marks)
Answer: Sodium and potassium are very reactive metals. They react vigorously with the oxygen and moisture in the air and even with cold water, often catching fire. To prevent these dangerous reactions and keep them away from air and water, they are stored under kerosene.
Q5. How is hydrogen gas produced and tested when a metal reacts with an acid? (3 marks)
Answer: When a metal such as zinc reacts with a dilute acid such as hydrochloric acid, a salt (zinc chloride) and hydrogen gas are formed: Metal + Dilute acid → Salt + Hydrogen. The hydrogen gas escapes as bubbles. To test it, a burning matchstick is brought near the mouth of the test tube; the gas burns with a characteristic "pop" sound, which confirms that the gas is hydrogen.
Q6. List any four exceptions among metals and non-metals. (2 marks)
Answer: (1) Mercury is a metal but is liquid at room temperature. (2) Sodium and potassium are metals but are very soft and can be cut with a knife. (3) Graphite is a non-metal but conducts electricity. (4) Iodine is a non-metal but is lustrous (shiny). (Also, diamond is a non-metal but is the hardest natural substance.)
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