Physical properties of metals

Metals have different physical properties.

Metals are solids at room temperature. When we say room temperature it means the temperature indoors. Gold, silver, sodium, potassium, iron, zinc are solid metals. However, mercury is an exception. Mercury occurs in liquid state at room temperature. Mercury is used in thermometers, blood pressure meters and barometers.

Metals show lustre. The word lustre means a gentle sheen or soft glow. Gold and silver ornaments shine as do most metallic things. Metals shine because they contain free electrons that vibrate when they come in contact with light. When the electrons vibrate, they produce their own light. The reflected light gives the metal a shiny, lustrous appearance.

Metals are malleable. Malleability is the ability of a metal to be hammered into thin sheets. Gold and silver plates and tin sheets are popular examples. Coins are made of ferritic stainless steel and cupro-nickel.

Metals are ductile. They can be drawn into thin wires. Wires of aluminium and copper are used to conduct electricity.

Both malleability and ductility are aspects of plasticity. It means the extent to which a solid material can be plastically deformed without fracture.

Metals are good conductors of heat. Metals conduct heat because they have free electrons in their atoms. When a metal is heated, the free electrons move, and transmit the heat to the nearest atoms.

Metals conduct electricity. Metals conduct electricity because the outermost electrons in their atoms are held by weak atomic forces, allowing these electrons to flow easily from one atom to another. This flow of electrons is responsible for the flow of electric current.

Metals conduct electricity because metal atoms have outer electrons which can move freely when an electric current is applied. Whereas copper wires are used in houses, aluminium cables are used outdoors.

This is because copper is more efficient than any other electrical conductor. Electrical wires are insulated to protect us from electric shocks.

Aluminium cables are used to conduct electricity to distant places because aluminium provides a better conductivity to weight ratio than copper. Aluminium has cost and weight advantages over copper wires.

In many places we see electricity cables high above the ground. These cables are mounted on a tower-like structure called a pylon. Aluminium provides a better conductivity to weight ratio than copper. Aluminium has cost and weight advantages over copper wires.

Metals show hardness. The hardness of metals differs. Hardness is generally characterized by strong intermolecular bonds. Hardness depends on the resistance offered when a compressive force is applied. Alkali metals like sodium and potassium are soft and can be cut with a knife.

Metals show varying melting point and boiling point. Metals like sodium and potassium have low melting and boiling points. Potassium melts at 63.5 °C and boils at 760 °C whereas sodium melts at 97.5 °C and boils at 883 °C.

The melting point of tungsten is 3422 °C and its boiling point is 5660 °C. The tungsten filament in an electric bulb offers resistance to the passage of electricity. This generates heat which is given out in the form of light.

Some metals have high melting points. The household utensils we use are made up of stainless steel, aluminium and copper since they can withstand high temperatures. The liquefied petroleum gas (lpg) we use in homes has a very high flame temperature. Similarly, many industrial processes require metal vessels because processing temperatures are very high.

Steel is an alloy of iron and carbon and stainless steel is made of iron and chromium. The melting point of steel is 1370 °C. The melting and boiling points of aluminium are 660.3 °C and 2467 °C and of copper are 1085 °C 2575 °C, respectively. The wok is made of cast iron whose melting point is 1204 °C. Iron melts at 1538 °C and boils at 2870 °C.

Metals produce a sonorous sound. The school bell, the temple bell and the church bell are made of bell metal. The bell metal is an alloy of copper and tin.