Metals and Non-metals

Elements are broadly classified as metals, non-metals, and metalloids based on their physical and chemical properties.

Physical Properties

Metals: Lustrous, hard (except Na, K), malleable, ductile, good conductors of heat and electricity, high melting points (except Hg, Ga), sonorous.

Non-metals: Non-lustrous (except iodine), brittle (if solid), non-malleable, poor conductors (except graphite), low melting points (except diamond and graphite).

Exceptions:
Mercury (Hg) is a liquid metal at room temperature.
Gallium (Ga) melts at 30°C.
Sodium (Na) and Potassium (K) are soft metals.
Graphite (carbon) is a non-metal that conducts electricity.
Iodine is a lustrous non-metal.

Chemical Properties of Metals

With oxygen: Metal + O2 → Metal oxide (basic in nature). 4Na + O2 → 2Na2O
With water: Metal + H2O → Metal hydroxide + H2. 2Na + 2H2O → 2NaOH + H2
With dilute acids: Metal + dilute acid → Salt + H2. Fe + H2SO4 → FeSO4 + H2
With salt solutions: More reactive metal displaces less reactive metal.

Reactivity Series (Activity Series)

K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Ag > Au

Metals above hydrogen react with dilute acids; metals below do not.

Ionic Bonding

Metals lose electrons (form cations) and non-metals gain electrons (form anions) to form ionic compounds.
Example: Na → Na+ + e- and Cl + e- → Cl-; together: NaCl

Properties of ionic compounds: High melting/boiling points, soluble in water (usually), conduct electricity in molten state or aqueous solution, crystalline solids.

Extraction of Metals

Very reactive metals (Na, Ca, Mg, Al): Electrolysis of molten chlorides/oxides
Moderately reactive metals (Zn, Fe, Pb): Reduction with carbon (coke) or CO
Less reactive metals (Cu): Reduction; some found free in nature
Very unreactive metals (Au, Ag, Pt): Found in free/native state

Gangue: Impurities in ore. Flux: Added to remove gangue (forms slag).

Corrosion and Prevention

Corrosion destroys metals gradually. Rusting: 4Fe + 3O2 + xH2O → 2Fe2O3.xH2O
Prevention: Painting, oiling, galvanisation (zinc coating), electroplating, alloying.
Alloy: Homogeneous mixture of metals (or metals + non-metals). Examples: Brass (Cu+Zn), Bronze (Cu+Sn), Steel (Fe+C), Solder (Pb+Sn).

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Example 1

Why is sodium stored under kerosene?
- Na is very reactive; it reacts vigorously with oxygen and water in air: 4Na + O2 → 2Na2O; 2Na + 2H2O → 2NaOH + H2.
- Kerosene prevents contact with air/moisture, making storage safe.

Example 2

Compare reactions of Na, Mg, and Fe with water.
- Na: Reacts vigorously with cold water, floats and catches fire: 2Na + 2H2O → 2NaOH + H2
- Mg: Reacts slowly with cold water; faster with hot water/steam.
- Fe: Does not react with cold or hot water; reacts with steam: 3Fe + 4H2O → Fe3O4 + 4H2

Example 3

What happens when copper is heated in air?
- 2Cu + O2 → 2CuO (black coating of copper oxide forms on the surface)
- On further heating the black coating turns back to reddish Cu inside a flame (reducing zone).

Example 4

Aluminium is more reactive than iron, yet iron corrodes more easily. Why?
- Aluminium forms a thin, strong, self-healing oxide layer (Al2O3) on its surface.
- This layer acts as a protective coating preventing further corrosion.
- Iron does not form such a protective layer; rust is porous and flaky.

Example 5

Thermite reaction: How is iron extracted from its oxide using aluminium?
- Fe2O3 + 2Al → Al2O3 + 2Fe + heat (very high)
- Al is more reactive and displaces Fe from its oxide.
- Used to weld railway tracks (thermite welding).

Example 6

Why do ionic compounds have high melting points?
- Ionic compounds consist of positive and negative ions held by strong electrostatic forces.
- A large amount of energy is needed to break these forces → high melting and boiling points.

Example 7

What is galvanisation and how does it prevent rusting?
- Galvanisation is coating iron/steel with a thin layer of zinc.
- Zinc is more reactive than iron; it reacts preferentially with oxygen and moisture.
- Even if zinc coating is scratched, zinc continues to protect iron by acting as a sacrificial anode.

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Common mistakes

Confusing malleable and ductile: Malleable = can be beaten into sheets; Ductile = can be drawn into wires.
Reactivity series: Memorise the order; metals above H2 react with dilute acids, those below do not.
Alloys are not compounds: An alloy is a mixture (homogeneous), not a pure compound.

Summary

Metals have characteristic physical properties (lustre, conductivity, malleability). Their reactivity follows the reactivity series. Ionic bond formation involves electron transfer. Metals are extracted by methods matching their reactivity. Corrosion is prevented by protective coatings and alloying.