LIWA

Matter and Its Composition

ICSE Class 7 · Chemistry · Chapter 1

What this chapter covers

Key definitions

Matter is anything that has mass and occupies space.

Mass is the amount of matter contained in an object.

Volume is the amount of space that an object occupies.

A solid is a form of matter that has a fixed shape and a fixed volume.

A liquid is a form of matter that has a fixed volume but no fixed shape.

A gas is a form of matter that has neither a fixed shape nor a fixed volume.

Particles are the extremely small pieces that every kind of matter is made of.

An atom is the smallest particle of an element that can take part in a chemical change.

A molecule is the smallest particle of an element or a compound that can exist on its own and still has the properties of that substance.

Intermolecular space is the gap between one particle of matter and the next.

Intermolecular attraction is the force of attraction that acts between the particles of a substance and holds them together.

Key points

Questions answered

Define matter. Name two things around you that are matter and two that are not.
Matter is anything that has mass and occupies space. A school bag and the water in a bottle are matter. Light and sound are not matter.
How could you show that air has mass?
Weigh a soft, deflated football, pump air into it and weigh it again. The mass increases, so the air pushed into it must have mass. A stick balancing two empty balloons also tilts when one balloon is filled with air.
A glass pushed mouth-down into water does not fill with water. Explain why.
The glass is full of air, and air occupies space. The trapped air keeps the water out until it is allowed to escape by tilting the glass.
Water rises from the 40 mL mark to the 55 mL mark when a key is dropped into a measuring cylinder. What is the volume of the key?
Volume of key = 55 mL − 40 mL = 15 mL, which is 15 cm3.
State one difference between a liquid and a gas in terms of shape and volume.
A liquid has a fixed volume but takes the shape of its container. A gas has no fixed volume or shape and spreads to fill the whole container.
When sugar dissolves in water, the water level hardly rises. What does this tell you about matter?
Matter is made of tiny particles with spaces between them. The sugar particles fit into the spaces between the water particles.
Describe how particles are arranged and how they move in a solid.
The particles are packed tightly in fixed positions, often in a regular pattern, with very small spaces between them. They can only vibrate about their fixed positions.
What is intermolecular attraction? In which state of matter is it strongest?
Intermolecular attraction is the force of attraction between the particles of a substance that holds them together. It is strongest in solids and weakest in gases.