States of matter
Matter is anything that occupies space. Matter exists in three states: solids, liquids and gases. Matter can be changed in various ways which includes physical, chemical and nuclear changes.
- a) Physical changes– they are normally reversible and no new substances formed. Examples are;
(i) Change of state such as melting and vaporization
(ii) Thermal expansion due to heating
(iii) Dissolving solids in liquids
(v) Charging electrically
- b) Chemical changes– they are irreversible and new substances are formed Examples are;
(i) Changes caused by burning
(ii) Changes occurring in some chemicals due to heating e.g. mercuric oxide
(iii) The reactions resulting from mixing chemicals to form other substances.
- c) Nuclear changes– these are changes occurring in nuclear substances which give off some particles i.e. Uranium and Radium. As this happens they change into other substances.
Particulate nature of matter
Matter is made up of millions of tiny particles which cannot be seen with naked eyes. These particles are called atoms and are made up of sub-atomic particles called protons, neutrons and electrons. Atoms join together to form molecules.
Movement of particles
Particles move from one region to another by the process of diffusion. Diffusion is the movement of molecules from regions of high concentration to regions of low concentration until an equilibrium is reached or achieved. Gases diffuse faster or readily than liquids.
The rate of diffusion depends on the manner of arrangement of individual particles.
Individual atoms in solids have a small space between them hence their forces of attraction are very strong. They vibrate in their fixed positions and this gives solids a fixed shape.
Forces of attraction between liquid molecules are not as strong as in solids where motion is not restricted. They collide with each other as they move about. They take the shape of the container they are put in hence have no definite shape.
Molecules of atoms in gaseous state are further apart experiencing very small forces of attraction. This makes them almost completely free from each other. We say they are independent in space. Gases have no definite shape and volume but they take up the space and volume of the container they are put in.