What is physical properties of metals?

Physical properties of metals — Chemistry Keypoint

Physical properties of metals are characteristics you can observe or measure without changing what the metal is made of. These include appearance, how metals conduct electricity and heat, their strength, and how they respond to force. These properties make metals useful for different purposes.

Quick Summary: Key Physical Properties

Lustrous (shiny appearance)
Good conductors of heat and electricity
Malleable (can be hammered into sheets)
Ductile (can be drawn into wires)
Sonorous (produce ringing sounds when struck)
High density and melting points
Hard but flexible (not brittle)

Understanding Physical Properties

Physical properties are features you can see, feel, or measure without changing the substance itself. When you look at an iron rod, touch copper wire, or hear a metal bell ring, you are observing physical properties.

These properties differ from chemical properties, which describe how a substance reacts with other substances. Physical properties answer questions like: What does it look like? How strong is it? Does it conduct electricity?

Detailed Physical Properties of Metals

1. Metallic Lustre (Shininess)

Metals have a shiny appearance called metallic lustre. This is why gold jewelry sparkles, aluminum roofing sheets reflect sunlight, and chrome-plated motorcycle parts look bright.

The shininess comes from how metal surfaces reflect light. Free electrons in metals can absorb light energy and re-emit it, creating that characteristic shine. When you polish a metal surface, you make it smoother so it reflects light better.

Nigerian examples:

Polished brass door handles in banks
Shiny aluminum pots in Nigerian kitchens
Chrome fittings on luxury cars
Silver-colored zinc roofing sheets

However, some metals lose their lustre when they react with air or moisture. Iron rusts and becomes dull brown. Aluminum forms a thin oxide layer but still looks fairly bright.

2. Electrical Conductivity

Metals are excellent conductors of electricity. This means electric current flows through them easily. Copper and aluminum are used for electrical wiring in homes, PHCN transmission lines, and electronic devices.

Why metals conduct electricity: Metal atoms have free electrons that can move throughout the metal. When you connect a battery or power source, these electrons flow, creating an electric current.

Best conductors (in order):

Silver (best but expensive)
Copper (most commonly used)
Gold (used in phones and computers)
Aluminum (used for power lines)

NEPA/PHCN uses aluminum cables for long-distance power transmission because aluminum is lighter and cheaper than copper, even though copper conducts slightly better.

3. Thermal Conductivity (Heat Conduction)

Metals conduct heat quickly from hot parts to cooler parts. This is why metal cooking pots heat up fast, why you use metal radiators to cool car engines, and why metal roofs get very hot under the Nigerian sun.

The same free electrons that conduct electricity also transfer heat energy through the metal. When one part of a metal spoon gets hot, the heat spreads rapidly to the other parts.

Practical applications:

Aluminum cooking pots heat food evenly
Iron clothing irons transfer heat to clothes
Copper pipes in solar water heaters
Steel radiators cool engines

Safety concern: Be careful touching metal under hot sun or near fire. A metal gate in Lagos afternoon heat can burn your hand. A wooden gate stays cooler because wood conducts heat poorly.

4. Malleability

Metals are malleable, meaning you can hammer them into thin sheets without breaking. Goldsmiths in Kano beat gold into thin sheets for jewelry. Panel beaters in Lagos reshape car body metal. Aluminum manufacturers roll aluminum into thin foil for food wrapping.

This property works because metal atoms can slide over each other in layers without breaking apart. The metallic bonds between atoms are strong but flexible.

Examples of malleability:

Gold can be hammered into sheets so thin they’re almost transparent (gold leaf)
Aluminum foil for wrapping food (your mum uses this in the kitchen)
Zinc sheets for roofing (common in Nigerian buildings)
Panel beaten car parts after accidents
Flattened metal sheets for building construction

5. Ductility

Metals are ductile, meaning you can pull them into thin wires without breaking. Copper wires in your house electrical wiring, aluminum cables for PHCN transmission, and steel cables supporting bridges all demonstrate ductility.

Wire-drawing machines pull heated metal through progressively smaller holes. The metal stretches thinner and thinner, becoming a wire. Gold is so ductile that one gram can be drawn into a wire 2 kilometers long!

Common ductile metals:

Copper: Used for electrical wiring (you see coiled copper wire in electronics markets)
Aluminum: Used for overhead power cables
Steel: Used for cables in bridges and construction
Gold: Used for fine wires in mobile phones and computers

Note the difference:

Malleable = can be hammered into sheets
Ductile = can be drawn into wires

6. Sonorousness

Metals are sonorous, meaning they produce clear ringing sounds when struck. Church bells, school bells, metal xylophones, and the “gong” sound when LASTMA officers hit traffic barriers all demonstrate sonorous metal.

Sound vibrations travel well through metals because metal atoms are closely packed and firmly bonded. When you hit a metal object, it vibrates and produces sound waves.

Uses of sonorous metals:

Church and mosque bells (brass, bronze)
School bells calling students to assembly
Musical instruments like cymbals and metallophones
Alarm systems and doorbells

Non-metals like plastic or rubber don’t ring when struck – they make dull thuds instead. This is one way to quickly identify metals.

7. High Density

Most metals have high density, meaning they are heavy for their size. A small piece of iron feels much heavier than a same-sized piece of wood or plastic.

Density is mass per unit volume (Density = Mass ÷ Volume). Metal atoms pack closely together, making metals dense.

Density comparison:

Metal	Density (g/cm³)	Common Use
Aluminum	2.7	Aircraft, light vehicles (relatively low density)
Iron	7.9	Construction, bridges
Copper	8.9	Wiring, pipes
Lead	11.3	Batteries, radiation shielding
Gold	19.3	Jewelry (very dense)

Exception: Sodium and potassium are metals with low density – they can float on water!

8. High Melting and Boiling Points

Most metals remain solid at room temperature and need high temperatures to melt. This is why you need a very hot furnace to melt iron for welding, or why gold melting requires intense heat.

Strong metallic bonds between atoms require a lot of energy to break. The free electrons act like glue holding metal atoms together.

Melting points of common metals:

Mercury: -39°C (liquid at room temperature – exception!)
Aluminum: 660°C
Copper: 1,085°C
Iron: 1,538°C
Tungsten: 3,422°C (highest melting point)

Welders in Lagos need extremely high temperatures to join metal parts. Blacksmiths heat metal red-hot before hammering it into shape.

9. Hardness

Most metals are hard and difficult to scratch or dent. Steel is hard enough to cut through wood. Diamond tools are needed to cut very hard metals.

However, some pure metals are softer:

Gold is soft (you can bite it – that’s how people test real gold)
Sodium is soft enough to cut with a knife
Lead is relatively soft and bends easily

To make metals harder, we create alloys. Steel (iron + carbon) is much harder than pure iron. Bronze (copper + tin) is harder than pure copper.

10. Strength and Flexibility

Metals are strong under tension (pulling) and compression (pushing). Steel beams hold up buildings. Iron rods reinforce concrete. Metal cables support bridges.

Unlike brittle materials (like glass or ceramics), metals don’t shatter when struck. Instead, they bend or dent. This makes metals safer for construction – a metal beam under too much load will bend and give warning before complete failure.

Physical vs Chemical Properties

Physical Properties	Chemical Properties
Observable without changing substance	Observed only during chemical reactions
Examples: color, density, melting point	Examples: rusting, burning, reacting with acid
Shiny appearance of copper wire	Copper turning green when exposed to air
Iron’s high density	Iron rusting in rain
Gold’s malleability	Gold not reacting with acids (except aqua regia)

Common Exam Mistakes to Avoid

WAEC examiners frequently report these errors:

Confusing malleability and ductility: Students say “metals can be drawn into sheets” (wrong – that’s malleability). Ductility = wires, Malleability = sheets.
Spelling errors: Writing “sonorus” instead of “sonorous”, “luster” instead of “lustre”, “malable” instead of “malleable”, “ductail” instead of “ductile”.
Giving chemical properties when asked for physical: Mentioning rusting or reaction with acids when the question asks for physical properties.
Not explaining WHY: Writing “metals conduct electricity” without explaining it’s due to free mobile electrons.
Incomplete definitions: Saying “metals are shiny” without using the correct term “metallic lustre”.
Forgetting exceptions: Stating “all metals have high melting points” (mercury is liquid at room temperature).

Practice Questions

Multiple Choice Questions

1. Which property allows metals to be hammered into thin sheets?
a) Ductility
b) Malleability ✓
c) Sonorousness
d) Conductivity

2. Metals conduct electricity well because they have:
a) High melting points
b) Shiny surfaces
c) Free mobile electrons ✓
d) High density

3. The property of metals that makes them suitable for making bells is:
a) Malleability
b) Ductility
c) Lustre
d) Sonorousness ✓

4. Which of these is NOT a physical property of metals?
a) High density
b) Metallic lustre
c) Rusting in moist air ✓
d) Good heat conduction

5. The metal with the lowest melting point that is liquid at room temperature is:
a) Sodium
b) Mercury ✓
c) Aluminum
d) Lead

Essay/Theory Questions

1. State and explain FIVE physical properties of metals. (10 marks)

Examiner’s tip: State each property clearly, then explain what it means and give an example. Don’t just list properties without explanation.

Model answer:

Metallic lustre: Metals have shiny surfaces that reflect light. Example: polished aluminum pots shine because free electrons reflect light waves.
Good electrical conductivity: Metals conduct electricity because they have free mobile electrons that carry electric current. Example: copper wires are used for electrical wiring.
Malleability: Metals can be hammered into thin sheets without breaking. Example: aluminum is rolled into thin foil for food wrapping.
Ductility: Metals can be drawn into wires. Example: copper is drawn into electrical wires used in homes.
High density: Metals are heavy for their size because metal atoms are closely packed. Example: a small piece of iron is much heavier than the same size of wood.

2. Distinguish between malleability and ductility. (4 marks)

Examiner’s tip: Define both terms clearly and explain the difference with examples.

Model answer:
Malleability is the ability of metals to be hammered or rolled into thin sheets without breaking. Example: aluminum foil and zinc roofing sheets.

Ductility is the ability of metals to be drawn into thin wires without breaking. Example: copper electrical wires and aluminum transmission cables.

The difference is that malleability produces sheets while ductility produces wires.

3. Explain why metals are good conductors of heat and electricity. (3 marks)

Examiner’s tip: Mention the electron structure and how it enables conduction.

Model answer:
Metals have free mobile electrons that can move throughout the metal structure. These electrons are not attached to any particular atom. When heat or electricity is applied, these free electrons move quickly, transferring energy through the metal. This makes metals excellent conductors of both heat and electricity.

4. Give THREE examples of how physical properties of metals make them useful in everyday life. (6 marks)

Examiner’s tip: Link specific properties to specific uses with clear explanations.