Chemistry is the scientific study of substances. Chemists investigate the properties (characteristics) of the substances that make up the universe. They study how those substances behave under different conditions. They attempt to explain the behavior of a substance in terms of the substance's structure and composition. Chemists also seek to understand chemical changes. Chemical changes involve alterations in a substance's chemical makeup. The combination of iron with oxygen from the air to form rust is a chemical change. Substances may also go through physical change without altering their chemical makeup. Water changes physically but not chemically when it freezes.
Chemical changes occur constantly in nature and make life on Earth possible. During a thunderstorm, for instance, lightning causes a chemical change in the air. The electrical energy and heat of a lightning bolt cause some of the nitrogen and oxygen in the atmosphere to combine and form gases called nitrogen oxides. The nitrogen oxides dissolve in raindrops that fall to the ground. In the soil, they are chemically changed into nitrates, substances that serve as fertilizer.
Chemical changes also occur as wood burns and becomes ashes and gases. The food we eat goes through many chemical changes in our bodies.
Chemists have learned much about the chemical substances and processes that occur in nature. In addition, chemical researchers have created many useful substances that do not occur naturally. Products resulting from chemical research include many artificial fibers, drugs, dyes, fertilizers, and plastics. The knowledge gained by chemists and the materials they have produced have greatly improved people's lives.
