Metals and non-metals — physical and chemical properties comparison

Question

Compare the physical and chemical properties of metals and non-metals. Give exceptions to the general rules.

(CBSE Class 8 and Class 10 — Metals and Non-Metals)

Property Comparison Decision Tree

flowchart TD
    A["Is the element a Metal or Non-Metal?"] --> B{Physical Test}
    B -->|Lustrous, malleable, ductile| C["Likely Metal"]
    B -->|Dull, brittle| D["Likely Non-Metal"]
    C --> E{Chemical Test}
    D --> F{Chemical Test}
    E -->|Forms basic oxide| G["Confirmed Metal"]
    E -->|Forms acidic oxide| H["Exception: check further"]
    F -->|Forms acidic oxide| I["Confirmed Non-Metal"]
    F -->|Forms basic oxide| J["Exception: check further"]
    G --> K["Examples: Na, Fe, Cu, Al"]
    I --> L["Examples: C, S, N, O"]

Solution — Step by Step

Property	Metals	Non-Metals
Lustre	Shiny (metallic lustre)	Dull (except iodine, diamond)
Hardness	Generally hard	Generally soft (except diamond)
Malleability	Can be beaten into sheets	Brittle, break when hammered
Ductility	Can be drawn into wires	Cannot be drawn into wires
Conductivity	Good conductors of heat and electricity	Poor conductors (except graphite)
State at room temp	Solid (except mercury — liquid)	Solid, liquid, or gas
Melting point	Generally high	Generally low
Sonority	Produce ringing sound when struck	Do not produce ringing sound

Reaction with oxygen:

Metals form basic oxides: $4\text{Na} + \text{O}_2 \rightarrow 2\text{Na}_2\text{O}$ (basic)
Non-metals form acidic oxides: $\text{S} + \text{O}_2 \rightarrow \text{SO}_2$ (acidic)

Reaction with water:

Reactive metals (Na, K) react vigorously with cold water
Moderately reactive metals (Fe, Zn) react with steam
Non-metals generally do not react with water

Reaction with acids:

Metals react with dilute acids to produce hydrogen gas: $\text{Zn} + 2\text{HCl} \rightarrow \text{ZnCl}_2 + \text{H}_2\uparrow$
Non-metals do not react with dilute acids (generally)

Mercury — Metal but liquid at room temperature
Graphite — Non-metal but conducts electricity
Diamond — Non-metal but extremely hard
Iodine — Non-metal but has metallic lustre
Sodium and potassium — Metals but soft (can be cut with a knife)
Aluminium oxide — Amphoteric (both basic and acidic)

Why This Works

The distinction between metals and non-metals comes from their atomic structure. Metals have fewer electrons in their outer shell (1-3) and tend to lose them, forming positive ions. This metallic bonding (sea of electrons) gives them conductivity, malleability, and lustre. Non-metals have more outer electrons (4-7) and tend to gain electrons, forming covalent bonds — resulting in brittle, non-conducting structures.

Alternative Method — Reactivity Series Connection

Metals can be ranked by reactivity: K, Na, Ca, Mg, Al, Zn, Fe, Pb, H, Cu, Ag, Au (most to least reactive). This series predicts reactions with water, acids, and displacement reactions.

CBSE exams love asking about exceptions. Memorise these five: mercury (liquid metal), graphite (conducting non-metal), diamond (hard non-metal), sodium/potassium (soft metals), and iodine (lustrous non-metal). They appear as 1-mark questions almost every year.

Common Mistake

Students often write “all metals are hard” or “all non-metals are gases.” These are wrong — sodium is a soft metal, and carbon (diamond) is a very hard non-metal. Always say “generally” or “most” when describing properties, and be ready with exceptions. Absolute statements lose marks in CBSE.