CBSE Class 8 Science — Metals and Non-Metals

Chapter Overview & Weightage

Metals and Non-Metals is one of the foundational chapters in Class 8 Science. It classifies materials into metals and non-metals based on physical and chemical properties, and introduces important reactions of metals with oxygen, water, and acids. This knowledge is directly applied in Class 10 Chemistry (Reactivity Series) and Class 12 (Electrochemistry).

In CBSE Class 8 annual exams, this chapter carries 8–12 marks. Common question types: compare properties (table format), write chemical equations for metal reactions, exceptions to properties, uses of metals and non-metals. Table-format answers score well and are faster to write.

Key Concepts You Must Know

1. Physical Properties of Metals:

Lustre: Shiny surface (e.g., gold, silver, copper)
Hardness: Most metals are hard (exception: sodium and potassium are soft, can be cut with a knife)
Malleability: Can be beaten into thin sheets (gold is most malleable)
Ductility: Can be drawn into wires (gold is most ductile; copper widely used for wires)
Conductivity: Good conductors of heat and electricity (exception: lead is a poor conductor)
High melting/boiling point (exception: mercury is liquid at room temperature; gallium melts slightly above room temp)
Sonorous: Produce a ringing sound when struck

2. Physical Properties of Non-Metals:

Generally non-lustrous (exception: iodine and graphite have lustre)
Brittle when solid (can’t be beaten into sheets — they shatter)
Non-malleable, non-ductile
Poor conductors of heat and electricity (exception: graphite is a good conductor)
Low melting/boiling point (most are gases at room temperature: H₂, O₂, N₂, Cl₂)
Non-sonorous

3. Chemical Properties of Metals:

Reaction	Equation	Example
With oxygen	Metal + O₂ → Metal oxide	$4Na + O_2 \to 2Na_2O$
With water	Metal + Water → Metal hydroxide + H₂	$2Na + 2H_2O \to 2NaOH + H_2\uparrow$
With acids	Metal + Acid → Salt + H₂	$Fe + H_2SO_4 \to FeSO_4 + H_2\uparrow$
With salt solution	More reactive metal displaces less reactive	$Fe + CuSO_4 \to FeSO_4 + Cu$

4. Metal Oxides are basic — they turn red litmus blue and react with acids.

5. Non-metal oxides are acidic — they turn blue litmus red and react with bases.

Exception: Water ( $H_2O$ ) is neither acidic nor basic (neutral oxide).

Important Formulas

With water (reactive metals):

2Na + 2H_2O \to 2NaOH + H_2\uparrow \quad (\text{vigorously})

Ca + 2H_2O \to Ca(OH)_2 + H_2\uparrow \quad (\text{slowly})

3Fe + 4H_2O \xrightarrow{\text{steam}} Fe_3O_4 + 4H_2 \quad (\text{with steam only})

Copper, silver, gold — do not react with water.

Zn + CuSO_4 \to ZnSO_4 + Cu

(Zinc is more reactive than copper, so it displaces copper from copper sulphate solution)

Solved Previous Year Questions

PYQ 1 — Compare metals and non-metals on any five properties (5 marks)

Property	Metals	Non-Metals
Physical state at room temperature	Mostly solid (exception: Hg is liquid)	Mostly gas; some solids (C, S, P); Br is liquid
Malleability	Malleable (can be beaten into sheets)	Brittle (shatter when beaten)
Ductility	Ductile (drawn into wires)	Non-ductile
Electrical conductivity	Good conductors	Poor conductors (exception: graphite)
Reaction with oxygen	Form basic oxides	Form acidic oxides

PYQ 2 — Why is sodium stored in kerosene oil? (2 marks)

Sodium is extremely reactive with oxygen and water in air. When exposed to air, sodium immediately reacts:

4Na + O_2 \to 2Na_2O

2Na + 2H_2O \to 2NaOH + H_2\uparrow

The reaction with water can be violent and even cause fire. Kerosene oil (a non-reactive, non-aqueous liquid) covers the sodium completely, cutting off contact with air and water, preventing these reactions.

PYQ 3 — What happens when zinc reacts with dilute sulphuric acid? Write equation (2 marks)

Zinc reacts with dilute sulphuric acid to give zinc sulphate and hydrogen gas:

Zn + H_2SO_4 \to ZnSO_4 + H_2\uparrow

The hydrogen gas is released as bubbles (effervescence). This is a classic test for hydrogen — hold a burning splint near the mouth of the test tube; it extinguishes with a “pop” sound.

Difficulty Distribution

Difficulty	Topics	Approximate %
Easy	Properties of metals/non-metals, uses, simple equations	45%
Medium	Exceptions, displacement reactions, metal oxides	35%
Hard	Reasoning questions, multi-step chemical equations	20%

Expert Strategy

Master the exceptions. CBSE loves to test exceptions:

Non-metal with lustre: iodine and graphite
Metal that is liquid: mercury
Non-metal that is liquid: bromine
Non-metal that conducts electricity: graphite
Metal that is poor conductor: lead
Metal stored in kerosene: sodium and potassium
Non-metals used in medicine: iodine, sulphur

For equations: Balance all equations. CBSE awards 1 mark for a balanced equation with state symbols.

Remember the pattern for metal + acid: “Metal + Acid → Salt + Hydrogen gas.” The salt name comes from (Metal + the acid’s anion): zinc + HCl → zinc chloride; iron + H₂SO₄ → iron sulphate. This pattern works for all metals that react with acids.

Common Traps

Trap 1: Writing that all metals react with water. Only highly reactive metals (Na, K, Ca) react with cold water. Iron reacts only with steam. Copper, silver, gold don’t react with water at all. Write the reactivity level explicitly.

Trap 2: Saying non-metals are always gases. While many non-metals are gases (O₂, N₂, H₂, Cl₂), several are solids at room temperature (carbon, sulphur, phosphorus, iodine) and one is liquid (bromine). Carbon includes both diamond (hardest natural substance) and graphite (soft conductor) — both non-metals.

Trap 3: Confusing malleability and ductility. Malleability = beaten into sheets. Ductility = drawn into wires. Gold is most malleable AND most ductile (but copper is commonly used for electrical wires because it’s cheaper and also highly ductile and conductive).