What Are Chemical Elements?

Chemical elements are pure substances composed of atoms that all share the same number of protons in their nucleus, a quantity called the atomic number. Each element is the simplest form of matter that cannot be decomposed by ordinary chemical means, and the 118 confirmed elements constitute the building blocks from which all ordinary matter is assembled. Elements are organized in the periodic table, a systematic arrangement that groups them by atomic number and aligns elements with similar electronic configurations in the same column, revealing periodic trends in reactivity, conductivity, and physical state; the IUPAC periodic table of elements is the internationally adopted reference.

The field draws on atomic physics, quantum mechanics, and inorganic chemistry to explain and predict elemental behavior. Understanding the properties of individual elements is foundational to materials science, semiconductor engineering, nuclear technology, and the broader chemical sciences.

Metals and Industrially Critical Elements

The majority of elements are metals, characterized by high electrical and thermal conductivity, malleability, and a tendency to lose electrons in chemical reactions. Among the elements listed in engineering and materials contexts, aluminum is the most abundant metal in Earth's crust and a structural material of major industrial importance, used wherever low density combined with corrosion resistance is required. Calcium and barium are alkaline earth metals that appear in dielectric ceramics, phosphors, and electrochemical systems. Bismuth, antimony, and arsenic occupy the border between metals and nonmetals; arsenic and antimony serve as dopants in silicon and germanium semiconductors, and bismuth appears in low-melting alloys and thermoelectric materials. Boron, though a metalloid, is used in neutron-absorbing control rods for nuclear reactors and as a dopant in p-type silicon. The NIST Chemistry WebBook provides authoritative thermophysical and spectroscopic data for these and other elements.

Carbon and Nonmetallic Elements

Carbon is unique among elements in its ability to form stable chains and rings, giving rise to organic chemistry and, by extension, biochemistry and polymer science. In its pure forms, carbon appears as graphite, diamond, fullerenes, and graphene, each with distinct electrical and mechanical properties: graphite is a conductor, diamond an insulator with exceptional hardness, and graphene a two-dimensional material with extraordinary electron mobility. Bromine is a halogen liquid at room temperature, used in flame retardants and photographic chemistry. Cadmium, while classified as a metal, behaves chemically more like the heavier chalcogens and appears in cadmium telluride photovoltaic cells and nickel-cadmium batteries, though its toxicity has prompted regulatory restrictions in many jurisdictions.

Radioactive and Synthetic Elements

Several elements in the listed set are radioactive, either naturally occurring or synthetically produced in nuclear reactors and particle accelerators. Actinium, the first member of the actinide series, is a naturally occurring alpha emitter used in targeted cancer radiotherapy research. Americium, a synthetic transuranic element produced by neutron bombardment of plutonium, is used in ionization-type smoke detectors and as a portable gamma-ray source for industrial gauging. Berkelium and californium are synthetic elements produced at the Lawrence Berkeley National Laboratory, where their nuclear properties are studied for fundamental science and for neutron source applications. Astatine, the rarest naturally occurring element in Earth's crust, is a halogen with potential use in targeted alpha-particle cancer therapy due to its short half-life and decay characteristics. Bohrium is a synthetic element with atomic number 107, produced in heavy-ion accelerators and studied primarily for its nuclear structure.

Applications

Chemical elements have applications in a wide range of disciplines, including:

• Semiconductor manufacturing, where silicon, arsenic, boron, aluminum, and cadmium are used as base materials and dopants
• Nuclear energy and medicine, through the use of actinides and radioactive isotopes of actinium and americium
• Energy storage and conversion, including batteries, fuel cells, and photovoltaic materials
• Structural and aerospace engineering, relying on the strength-to-weight properties of aluminum and its alloys
• Biomedical applications, where trace elements serve physiological roles and radioisotopes enable imaging and therapy