Chemistry is the science that deals with matter and the changes that it undergoes. It is a study of the composition, structure, and properties of matter and of the changes that occur in matter.

Perhaps the only permanent thing in the world is change. Iron rusts, snow melts, paints peel off and f ire woods burn. We grow up, we grow old. Living plants and animals undergo ceaseless change, and even dead animals and plants continue to change as they decay. Such changes fascinated people and inspired them to look more closely at nature’s way of working.

Matter also undergoes other kinds of changes called physical changes. These changes differ from chemical reactions in that the involved substances do not change their identities. For example, water remains H₂O whether it is in solid state (ice), liquid water or gaseous state (steam). Physical change also involves making or separating mixtures. Dissolving table salt (NaCl) in water is a physical change.

Branches of chemistry

The study of modern chemistry has many branches, but can generally be broken down into five main disciplines, or areas of study. These are:

• Physical chemistry: Physical chemistry is the study of macroscopic properties, atomic properties, and phenomena in chemical systems.
• Organic chemistry: Organic chemistry deals with the study of substances containing carbon.
• Inorganic chemistry: Inorganic chemistry is the study of substances that, in general, are not primarily based on carbon.
• Analytical chemistry: Analytical chemistry involves the study of the composition of matter. It focuses on separating, identifying, and quantifying chemicals in samples of matter.
• Biochemistry: Biochemistry is the study of chemical processes that occur in living things. Research may cover anything from basic cellular processes up to understanding disease states so that better treatments can be developed.