Chemical elements
Introduction
Chemical elements are pure substances consisting of a single type of atom distinguished by its atomic number, which is the number of protons in its nucleus. The term "chemical element" is often used interchangeably with "element," which refers to a broader class of atoms distinguished by their atomic number. There are currently 118 confirmed elements, from hydrogen, which has one proton, to oganesson, which has 118 protons. Elements can be divided into metals, nonmetals, and metalloids.
History of Discovery
The concept of chemical elements dates back to ancient times. However, the first scientific discovery of an element occurred in the 17th century when Hennig Brand discovered phosphorus. In the 19th century, Dmitri Mendeleev created the periodic table, predicting the properties of elements yet to be discovered. As of 2021, all 118 elements have been discovered or synthesized, with the most recent addition being Tennessine in 2016.
Classification of Elements
Chemical elements can be classified in several ways, most commonly by metallicity, phase of matter (solid, liquid, or gas), and occurrence in nature.
By Metallicity
Elements are classified as metals, nonmetals, or metalloids based on their physical and chemical properties. Metals, such as iron and gold, are typically shiny, malleable, and good conductors of heat and electricity. Nonmetals, such as oxygen and carbon, lack these properties. Metalloids, such as silicon and arsenic, have properties in between.
By Phase of Matter
At room temperature, most elements are solids, but several are gases, and only two, bromine and mercury, are liquids. The phase of an element can provide clues about its physical properties.
By Occurrence
Elements are also classified by whether they occur naturally on Earth. Most elements are naturally occurring, but some, such as technetium and the transuranium elements, are only produced synthetically.
Properties of Elements
Each element has a unique set of physical and chemical properties that determine its behavior in chemical reactions, its state of matter, and its role in the natural world.
Physical Properties
Physical properties of elements include density, melting point, boiling point, and color. These properties are determined by the structure of the element's atoms and the nature of the chemical bonds between them.
Chemical Properties
Chemical properties of elements include reactivity, electronegativity, and the types of chemical bonds they can form. These properties are largely determined by the configuration of electrons in an element's atoms.
Uses of Elements
Elements have a wide range of uses in industry, medicine, and everyday life. For example, aluminum is used in construction and transportation, silicon in electronics, and helium in balloons. Radioactive elements such as uranium are used in nuclear power plants and medical imaging.