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 behaviour 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.

Major branches of chemistryof chemistry

Analytical chemistry determines the properties of chemical substances and the structure and composition of compounds and mixtures.
Qualitative analysis identifies the types of elements and compounds that make up substances.
Quantitative analysis measures the amounts of the different chemicals that make up substances.
Radiochemistry involves the identification and production of radioactive elements and their use in the study of chemical processes.
Applied chemistry refers to the practical use of the knowledge of chemical substances and processes.
Agricultural chemistry develops fertilizers and pesticides and studies the chemical processes that occur in the soil and that are involved in crop growth.
Environmental chemistry studies, monitors, and controls chemical processes and other factors in the environment and their relationships to living things.
Industrial chemistry involves the chemical production of raw materials and the development, study, and control of industrial chemical processes and products.
Biochemistry deals with the chemical processes of living organisms.
Inorganic chemistry concerns chemical substances that do not contain carbon-to-carbon bonds.
Organic chemistry is the study of chemical substances that contain carbon-to-carbon bonds.
Physical chemistry interprets chemical processes in terms of physical properties of matter, such as mass, motion, heat, electricity, and radiation.
Chemical kinetics studies the sequence of steps in chemical reactions and the factors that affect the rates at which chemical reactions proceed.
Chemical thermodynamics deals with the energy changes that occur during chemical reactions and how temperature and pressure differences affect reactions.
Nuclear chemistry is the use of chemical techniques in the study of nuclear reactions.
Quantum chemistry analyzes the distribution of electrons inmolecules and interprets the chemical behavior of molecules in terms of their electron structure.
Radiation chemistry concerns the chemical effects of high-energy radiation on substances.
Solid-state chemistry deals with the composition of solids and the changes that occur within and between solids.
Stereochemistry studies the arrangement of atoms in molecules and the properties that follow from such arrangements.
Surface chemistry examines the surface characteristics of chemical substances.
Polymer chemistry deals with plastics and other chainlike molecules formed by linking many smaller molecules.
Synthetic chemistry involves combining chemical elements and compounds to duplicate naturally occurring substances or to produce compounds that do not occur naturally.k of chemists

The work of chemists

Chemistry involves the study of many substances. Substances differ greatly in properties, structure, and composition. The methods chemists use and the questions they attempt to answer also differ greatly. However, all chemists share certain fundamental ideas.

Fundamental ideas of chemistry. The most basic chemical substances are the chemical elements. They are the building blocks of all other substances. Each chemical element is made up of only one kind of atom. The atoms of one element differ from those of all other elements. Chemists use letters of the alphabet as symbols for the elements. The symbols for the elements carbon, hydrogen, oxygen, and iron, for example, are C, H, O, and Fe. There are 91 elements known to exist on earth. An additional 20 elements have been produced artificially.

The broad range of study. Chemists study substances according to questions they want to answer. Many chemists study special groups of substances, such as compounds containing carbon-to-carbon bonds. Some chemists specialize in techniques that enable them to analyse any substance and identify the elements and compounds it consists of. Other chemists study the forces involved in chemical changes. Much chemical research deals with the atomic and molecular structures of substances. Certain chemists try to predict chemical behaviour from theories about the forces at work within the atom. Chemists also work to create new substances and to make synthetic forms of rare but useful natural materials. Their field is called synthetic chemistry. A number of chemists apply their knowledge to finding ways of using substances and chemical processes in agriculture, industry, medicine, and other fields.

In some cases, chemistry overlaps such sciences as biology, geology, mathematics, and physics to such an extent that interdisciplinary sciences have been established. Biochemistry, for example, combines biology and chemistry in studying the chemical processes of living things. Geochemistry is the study of the chemical processes that take place on the earth and in the atmosphere. Geochemists also study the composition and chemical structure of rocks and minerals. Astrochemistry deals with the composition of matter in stars and in interstellar space.

Tools and techniques. Chemists use a wide variety of tools and techniques. Specialized instruments and electronic computers help chemists make accurate measurements. A device called a mass spectrometer, for example, enables chemists to determine the mass and atomic composition of molecules. Mass is the total quantity of matter that anything contains. Chemists can identify how atoms are arranged in molecules by using instruments that measure the radiation absorbed and given off by the molecules. A technique called chromatography enables chemists to separate complicated mixtures into their parts and to detect and measure low concentrations of substances, such as pollutants in air and water.