Mass and Matter 18 18.2 The atomic nature of matter
Atoms are tiny particles that are the building blocks of matter. Atoms contain even smaller particles but these sub-atomic particles are not easily separated from each other. (The structure of the atom is examined in Chapter 22.) All matter is made from atoms. When atoms join together they form molecules. For example, carbon dioxide is made of molecules. A carbon dioxide molecule has 1 carbon atom and 2 oxygen atoms joined together. Atoms and molecules are together referred to as particles of matter.
Atom of Oxygen
Atom of Carbon
Fig. 6 A single molecule of carbon dioxide
Particles are moving all the time. Their movement is random. Sometimes they move very little and sometimes they move a lot. How the particles in an object move in relation to one another accounts for the state of matter of the object.
18.3 States of matter
By observing materials in a variety of different situations scientists have identified three states of matter: solid, liquid and gas. Scientists identify the state of matter of an object by observing its properties. Properties of matter may include shape, volume, colour and texture as well as many others. (See Chapter 21: Properties of Materials).
Fig. 7 The three states of matter: solid, liquid and gas.
Solids Solids are identified as materials that: Have a definite shape Have a definite volume Cannot be easily compressed Cannot flow
l l l l
Fig. 8 Molecules in a solid.
The atomic nature of matter accounts for these properties by suggesting that the particles (atoms or molecules) in a solid are tightly packed together. They move a little (vibrate) but stay close to one another. Ice is an example of a solid.