A matter of importance
Francine Taylor-Campbell, Contributor

Welcome to another aids to chemistry series. This year, we hope to use simple questions to assess our understanding of the fundamental concepts in the subject.

Students should be able to:

• Explain the differences in the three states of matter, in terms of energy and particle arrangements.
• State the evidence that supports the particulate nature of matter.
• Describe the structure of atoms.

What is matter?

• Matter has mass and occupies space. The quantity of matter in a material is determined by its mass.
• The state that matter occupies depends on how the particles in it are packed.
• The three states of matter are solid, liquid and gas.
• Matter can be changed from one form to another by increasing or decreasing the kinetic energy of the material.
• Processes such as freezing, melting and boiling can change the form that matter takes.
• All substances are made of atoms. These combine to form elements which later form compounds.

What are the main differences in the three states of matter?

The three states of matter can be differentiated based on their volume, shape and the energy, arrangement and forces operating between particles.

A solid has a fixed shape and volume, with the particles arranged in a regular, repeated pattern. The fixed shape is maintained by the strong forces of attraction between the particles, hence they have little kinetic energy and can only vibrate in their positions. These fixed positions mean that solids are difficult to compress and expand.

In comparison, a liquid, while having a fixed volume, takes on the shape of the container in which it is placed. The particles in a liquid are arranged randomly with small spaces between them enabling them to move easily. The moderate attraction and energy of the particles enable them to move, but not to separate from each other. The small spaces present help the liquid to be easily compressed or expanded.

The particles in a gas, however, can fill any space in which they are placed, due to the large amounts of kinetic energy that they possess. This means that a gas has no defined shape as the particles are arranged randomly with large spaces between them. The weak forces of attraction between the particles of a gas also enable them to move rapidly and as far away from each other as possible. A gas can, therefore, be easily compressed or expanded.

How can matter be changed from one form to another?

When the temperature of a piece of ice is increased, for example, particles gain kinetic energy and will begin to move, changing their regular-ordered structure to that of a liquid. This represents the process of melting and the ice will change to water. Further increases in temperature will change the water to steam (gas), as the particles get more energy to move away from each other. This is called boiling and evaporation.

To reverse this process, the temperature is decreased by cooling (condensation) and freezing. A solid can also be changed directly into a gas (without becoming a liquid) by the process of sublimation. A common example is the use of dry ice, which changes to the gas carbon dioxide.

These processes represent the different ways in which matter can be changed from one form to another.

Jamaica's future scientists test their skills during a chemistry lab at the Winston Jones High School, recently. - Photo by Michael Lee

Wow! Chemistry can be amazing. - Photo by Michael Lee

Francine Taylor-Campbell is an independent contributor.