Properties of Metals and Alloys | Chemistry

📖 In-Depth Theory

Metals as Giant Metallic Structures

METALS have GIANT METALLIC STRUCTURES — a regular lattice of positive metal ions surrounded by a sea of delocalised electrons.

This gives metals their characteristic properties:

HIGH MELTING AND BOILING POINTS:

Strong electrostatic forces between positive ions and the electron sea throughout the lattice.

Large amounts of energy needed to break these forces.

(Exceptions: mercury −39°C and gallium 30°C are liquids at or near room temperature.)

MALLEABLE — can be hammered into shapes:

Layers of ions can slide over each other — the electron sea re-accommodates ions in new positions.

No direction-specific bonds that would snap when layers move.

DUCTILE — can be drawn into wires:

Same reason as malleability — ions can slide into new positions without breaking the structure.

HIGH DENSITY — most metals are dense:

Close-packed lattice of heavy atoms.

Metals as Electrical and Thermal Conductors

Metals are the BEST conductors of electricity and heat among common materials.

ELECTRICAL CONDUCTIVITY:

Delocalised electrons can move freely through the metallic lattice.

When a VOLTAGE is applied, electrons drift in a specific direction → electric current.

This works in SOLID state — electrons can move even in a solid lattice.

Examples: copper (best common conductor), aluminium, iron, silver.

THERMAL CONDUCTIVITY:

Delocalised electrons also transfer kinetic (heat) energy rapidly through the structure.

Thermal energy is passed from hot regions to cool regions by electron movement.

This makes metals excellent heat conductors.

Examples: copper for cooking pans, aluminium for heat sinks in electronics.

This is why BOTH electrical and thermal conductivity improve together in metals — both rely on the same delocalised electron sea.

Alloys

ALLOYS are MIXTURES containing a metal and one or more other elements (often another metal or carbon).

Why alloys form:

Pure metals are often too SOFT for practical use.

Adding a different element disrupts the regular lattice — making it HARDER.

How alloys work:

In a PURE METAL, all ions are the same size — layers can slide easily → soft.

In an ALLOY, DIFFERENT SIZED atoms are inserted into the lattice.

They distort the regular pattern → layers CANNOT slide as easily → harder and stronger.

Key alloys and their applications:

STEEL (iron + 0.1–2% carbon): much harder than iron → construction, tools, vehicles, bridges.

STAINLESS STEEL (iron + chromium + nickel): resists corrosion → cutlery, surgical instruments.

BRONZE (copper + tin): harder than copper → ship propellers, statues, bearings.

BRASS (copper + zinc): golden appearance, harder than copper → musical instruments, taps.

ALUMINIUM ALLOYS (+ copper, magnesium etc.): strong and lightweight → aircraft, spacecraft.

⚠️ Common Mistake

Metals conduct electricity in the SOLID state — unlike ionic compounds which only conduct when molten or dissolved. This is because metallic conduction uses DELOCALISED ELECTRONS (which are already free to move in the solid), whereas ionic conduction requires ions to move (which they can't do when fixed in a solid lattice).

📌 Key Note

Metallic structure: positive ions + delocalised electrons. High MP/BP, malleable, ductile (layers slide). Conducts electricity AND heat in solid state (delocalised electrons). Alloys: different-sized atoms disrupt regular lattice → harder. Steel, bronze, brass are key examples.

🎯 Matching Activity — Metal or Alloy — Property Match

Match each substance to its key property and use. — drag the symbols on the right to match the component names on the left.

Copper

Drop here

Steel

Drop here

Bronze

Drop here

Aluminium alloys

Drop here

Stainless steel

Drop here

Best common electrical conductor — used in wiring and circuits

Iron + chromium + nickel — resists corrosion — used in cutlery and surgical instruments

Lightweight and strong — used in aircraft construction

Iron + carbon — harder than pure iron — used in construction and tools

Copper + tin — harder than pure copper — used in bearings and statues

🎯 Test Yourself

Question 1 of 2

1. Why can metals conduct electricity in the solid state, but ionic compounds cannot?

2. Why is brass (copper + zinc) harder than pure copper?

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🧪 Properties of Metals and Alloys

Metals as Giant Metallic Structures

Metals as Electrical and Thermal Conductors

Alloys

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