|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
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
Stereochemistry studies the arrangement
of atoms in molecules and the properties that follow from
Surface chemistry examines the surface
characteristics of chemical substances.
Polymer chemistry deals with plastics and
other chainlike molecules formed by linking many smaller
Synthetic chemistry involves combining
chemical elements and compounds to duplicate naturally occurring
substances or to produce compounds that do not occur naturally.k
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
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
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.