Organic chemistry

Organic chemistry deals with compounds that are related to living things. It focuses only on compounds featuring the element carbon. The vast majority of known compounds belong to this group. Organic compounds can be very complex because of certain features of the carbon atom. Carbon atoms have the unusual ability to combine with each other to form rings or long chains. No other element does so as extensively. Carbon will also combine with many different atoms or groups of atoms. These properties make carbon the most versatile of all elements in forming compounds. Some natural organic compounds include carbohydrates, proteins, and vitamins. Chemists have also created many new organic compounds, including plastics, drugs, and agricultural chemicals.

Inorganic chemistry

Inorganic chemistry focuses on elements and compounds that contain little or no carbon. Examples of inorganic compounds include common salt (a combination of sodium and chlorine) and ammonia (nitrogen and hydrogen). The study of such simple inorganic compounds as salt has led to some of the fundamental concepts of modern chemistry. One of those ideas is that for most pure chemical substances the elements are always present in fixed proportions. Chemists once thought that these inorganic elements were not associated with living things. They have since discovered that small amounts of inorganic elements—specifically, some metals—are essential for some biological processes such as respiration, nerve function, and the growth of cells.

Physical chemistry

Physical chemistry seeks to measure and explain the physical changes that take place in chemical processes. It is concerned with the interactions between substances rather than with the structure of the substances. This branch is closely related to the science of physics, which explains how matter behaves and how it is affected by energy. Physical chemists work in very specific areas. Some seek to measure and understand the rates of chemical reactions. Others study the effects of certain forms of energy, such as electricity and light, on chemical reactions. (See also physics.)

Analytical chemistry

Analytical chemistry is used to determine which elements are in a particular substance and how much of each element is there. The analysis involves taking the substances apart to look at their individual elements. This branch can be used to fight pollution because analytical chemists can examine the waste from a factory and determine what kinds of chemicals it contains. Scientists can then determine how best to get rid of the waste.

Industrial chemistry

Industrial chemistry involves chemicals used in industry. Chemists play an important role in the manufacture, inspection, and safe handling of such chemicals. They can provide the chemicals that are used as raw materials to make other products, such as textiles, metals, and paint. Chemists can also help develop new products. Pharmaceutical firms, for example, operate large research laboratories. Chemists in these laboratories test molecules to determine if they can be used to treat diseases.

Biochemistry

Biochemists use the techniques and theories of chemistry to understand the processes that occur in living things. This field combines chemistry, physics, and biology. Biochemists have established, among other things, the principles that underlie energy transfer in cells, the chemical structure of cell membranes, the way that traits are passed from one generation to another, and muscular and nerve function. Biochemical discoveries have had a great impact on the understanding and treatment of disease. Many diseases result from disruptions in normal biochemical processes. Frequently, drugs can help deal with these diseases. Discovering how drugs work is another major area of study in biochemistry. (See also biochemistry.)

Polymer chemistry

In the 20th century the new field of polymer chemistry was developed. Polymer chemistry focuses on compounds called polymers. These are large molecules made up of many smaller molecules (monomers), usually joined together in a chain. They can be organic or inorganic. They occur naturally and they can be created by chemists. Natural polymers make up many of the materials in living organisms, including, for example, proteins, cellulose, and DNA. Therefore the study of polymers can overlap with biochemistry. Many artificial polymers, such as plastics and nylon, are used in industry.

Early ideas

The ancient Greeks were among the first to try to explain the nature of matter. In doing so they developed the first theories about chemistry. They developed the idea of the atom, and they suggested that all substances were made from combinations of earth, air, water, and fire.

But the idea of experimenting with different substances began in the Middle Ages. The first people to experiment with changing one substance into another were called alchemists. They attempted to make gold from lead and other common metals, to find a universal cure for disease, and to discover a substance that could give everlasting life. Although many of their ideas were incorrect, the alchemists did identify many chemicals and experimented with reactions between them. Their research paved the way for modern chemistry.

Beginnings of modern chemistry

In 1661 Robert Boyle, a British scientist, published a book called The Sceptical Chymist. In the book he recognized the basic nature of a chemical element. He argued that the four Greek elements could not be the real chemical elements because they cannot combine to form other substances and they cannot be extracted from other substances. Boyle suggested that there were many different elements in the world and stressed the need for careful experimentation to find and study them.

In the following century chemists conducted such experiments. Their work began to make clear which substances could be broken down into elements and which could not. In the late 18th century Henry Cavendish discovered hydrogen, and oxygen was discovered independently by the Swedish chemist Carl Scheele and by the British scientist Joseph Priestley.

The French chemist Antoine Lavoisier explained the process of burning. Before Lavoisier's time, people thought that everything that could be burned contained a substance called phlogiston. They believed that when burning took place, phlogiston was given off. Lavoisier found that when things burned they really combined with oxygen, and phlogiston did not exist. His work helped to get rid of the idea that fire was associated with magic. Lavoisier also helped develop the law of conservation of mass and started the modern system for naming elements and their compounds.

The 19th century

The next great step in explaining chemical changes was made in 1803 by a British schoolmaster, John Dalton. He applied the Greek idea of atoms to chemistry. Dalton said that all elements were made up of tiny particles that could not be divided into anything smaller. He also said that elements combined because their atoms joined together in simple numbers to form compound atoms, or molecules.

As the list of different elements grew in the 19th century chemists attempted to group them together according to their chemical properties. In 1869 the Russian chemist Dmitry Mendeleyev produced the first such classification. He created a table of the elements in which the elements were arranged according to similarities in their properties.

Mendeleyev's table was later refined as chemists discovered more elements and learned more about the properties of atoms. The modern version of the periodic table contains more than 100 elements, 92 of which are found in nature. Those not found in nature are made by bombardment of other molecules with high-energy particles.

Modern developments

In the late 19th century two discoveries led to revolutions in the fields of chemistry and physics. In 1896 scientists found that certain atoms naturally give off energy in the form of rays. This process is called radioactivity. Scientists soon learned to make other atoms radioactive and to control the process. This led to the development of nuclear energy and weapons as well as the use of radiation in medicine and industry.

The other major discovery, made in 1897, was that atoms are not simple, solid objects. British scientist J.J. Thomson found that they contain particles that eventually came to be called electrons. As scientists researched radioactivity over the next several decades they learned that atoms contain a nucleus and other particles called protons and neutrons and that these particles are arranged in a complex structure. These discoveries helped explain how atoms form bonds with other atoms to create molecules.

In the 20th century chemists created hundreds of new substances that provided both benefit and potential harm to the world. There are many new drugs to help people suffering from disease, new building materials, and new fertilizers to help crops grow. At the same time, however, scientists have learned that the chemicals in waste products from industries and nuclear energy plants must be dealt with so that they do not contaminate the land, water, and air. The challenge facing chemists at the beginning of the 21st century was to balance the need for new products with the desire to maintain the health of people and the planet.