LIWA

Metals and Non-metals

ICSE Class 7 · Chemistry · Chapter 6

What this chapter covers

Key definitions

Lustre is the shine that a freshly cut or polished surface of a substance shows when light falls on it.

Malleability is the property of a substance by which it can be beaten into thin sheets without breaking.

Ductility is the property of a substance by which it can be drawn into thin wires.

Sonority is the property of a substance by which it produces a ringing sound when it is struck.

Density is the mass of a substance contained in a unit volume.

Strength is the ability of a material to bear a heavy load or a strong pull without breaking.

Corrosion is the slow eating away of the surface of a metal when it reacts with substances in its surroundings, such as air, water and acids.

Rusting is the corrosion of iron, in which iron reacts with oxygen and moisture to form a reddish-brown substance called rust.

Rust is a reddish-brown, flaky substance made mainly of hydrated iron oxide, formed when iron combines with oxygen in the presence of water.

Galvanisation is the process of coating iron or steel with a thin layer of zinc to protect it from rusting.

Tinning is the process of coating iron or steel with a thin layer of tin.

Chrome plating is the process of depositing a thin layer of chromium on the surface of iron or steel using electricity.

Key points

Questions answered

Define malleability and name one metal used because it is malleable.
Malleability is the property of a substance by which it can be beaten into thin sheets without breaking. Aluminium is rolled into foil because it is malleable.
Why are electric wires made of copper while their outer covering is made of plastic?
Copper is a good conductor of electricity, so current flows through it easily. Plastic is an insulator, so it stops the current from reaching your hand and prevents shocks.
Name a non-metal that conducts electricity and a metal that is liquid at room temperature.
Graphite (a form of carbon) conducts electricity; mercury is a liquid metal.
A student says, "Sodium floats on water, so it must be a non-metal." Is the student right?
No. Sodium has a low density, which is unusual for a metal, but it is shiny when freshly cut and conducts electricity. One unusual property does not change its group; sodium is a metal.
What two things must be present for iron to rust? Write the word equation for rusting.
Oxygen (air) and water (moisture). Iron + oxygen + water → rust (hydrated iron oxide).
In the three-test-tube activity, why does the nail in the tube with quicklime not rust?
Quicklime absorbs moisture, so the air in the closed tube is dry. Without water, iron cannot rust even though oxygen is present.
How would you show that rust is basic in nature?
Shake a little rust in water and dip red litmus paper into it. The red litmus turns blue, which shows that rust is basic.
Why are iron water pipes galvanised and not simply painted?
Zinc coating covers the iron and also protects it where it is scratched, because zinc corrodes in place of iron. Paint inside a pipe would wear away and could get into the water.