A chemical element is a basic substance found in nature. It is something that cannot be broken down into simpler substances by using ordinary chemical processes. The elements are the building blocks for all other substances. When they are combined with other elements the result is called a compound. For example, water is a chemical compound of the elements oxygen and hydrogen.

Symbols of elements

Every element has a name as well as a symbol that is used to represent that name. Where possible, the capitalized first letter in the name of the element is used as the symbol. Therefore H is used for hydrogen, O for oxygen, and C for carbon. Symbols for other elements use two letters: He is used for helium and Cl for chlorine. In some cases, the element has a Latin name in addition to its English name and the symbol is taken from the Latin name. For example, Au is the symbol for gold, whose Latin name is aurum. Symbols for compounds are often constructed from those of the elements involved. Water, which is two parts hydrogen and one part oxygen, is written as H₂O.

How elements were discovered

Thousands of years ago people began to wonder whether there were certain substances that were basic to all matter. Some people in ancient Greece believed that all matter was made up of four elements—air, earth, water, and fire. This concept of an element was accepted for about 2,000 years. The work of people known as alchemists changed that idea, however. During the Middle Ages, which lasted from about 500 to 1500 AD, alchemists tried to change lead and other metals into gold using chemical processes. They failed in that effort, but in the course of their experiments with mixing and heating materials they discovered new elements and learned about the characteristics of elements. This work led to the science of chemistry.

In 1661 an English chemist named Robert Boyle realized that the four Greek “elements” could not be the basic building blocks of all matter. They could not be combined to make other substances, and they could not be obtained by breaking down other substances. He stressed the physical nature of elements and explained how they are combined to form compounds. This led scientists to look at common substances in a new way. Gold, silver, and lead, for example, had been known since ancient times, but they were not identified as elements until the 18th century. Scientists began to identify other substances as elements as well. By 1800, 23 elements were known, and as the tools of chemistry improved the rest were discovered.

Elements and atoms

All matter is composed of atoms. Every atom, in turn, has the same basic parts, including particles called protons, neutrons, and electrons. The properties of the atom, or the way it behaves, are determined by the numbers of these particles and the way they are arranged. The reason elements are considered basic substances that cannot be broken down further is that they are each made up of only one type of atom. This means that all atoms of an element have the same number of protons and electrons. Each element has a different number of protons. This number is called the atomic number. For example, the atomic number of hydrogen is 1 because a hydrogen atom has one proton.

Periodic table

In 1869 a Russian scientist named Dmitry Mendeleyev proposed a way of organizing the elements based on their chemical properties. The arrangement of elements that evolved from his idea is called the periodic table of the elements. It has become a principal tool for thinking about elements and the properties associated with them. Rows in the table are arranged by increasing atomic number of the elements. The columns are arranged in groups or “families” of elements exhibiting similar chemical characteristics.