What is an Element?

Element is the basic building block of all matter. It is the fundamental material of which all substances are composed; it is the substance that cannot be changed or transformed into any other material by chemical reactions. The term element is also used to refer to the basic features that characterize an object, a process or a problem: to be in one's element means to be at one's best; a brick wall has elements of clay and iron. Other words like component, constituent and ingredient have similar meanings but are less specific: they suggest a part that goes into the making of a whole or complete system or compound.

Until recently, there were only 118 known elements. The first list of elements was published in 1789 by Antoine-Laurent Lavoisier, who defined an element as any substance that could not be broken down into simpler substances by chemical processes. This definition comes close to the present-day one.

Elements are pure substances whose atoms all have the same number of protons. The number of protons determines the shape and size of an element's nucleus, which in turn determines the properties it has. The atoms of an element contain neutrons as well, and changing the number of neutrons does not change its elemental nature. Nevertheless, the number of protons and neutrons does determine the element's weight, so that it is possible to classify elements by their atomic numbers.

The seven original elements were recognized for their unique properties by the ancient Greeks, and they are mentioned in both the Bible and the Caraka-samhita, an Indian medical treatise. In the early 1800s, John Dalton proposed atomic theory and was able to assign atomic weights to many of the elements. Later, Dimitri Mendeleev arranged the known elements into groups according to their physical and chemical characteristics, and he made predictions about then unknown elements based on this arrangement.