Elements

Elements are the fundamental substances that cannot be broken down into simpler substances by chemical means. Each element is defined by the number of protons in its nucleus, its atomic number, which determines its identity and its place in the periodic table.

Most elements occur as atoms or in combination as ions and molecules in matter. In chemical reactions, elements rearrange to form compounds, while the total amount of each element is conserved.

The periodic table arranges known elements by increasing atomic number and electron configuration. Its rows and columns reflect recurring trends in properties, and groups such as the alkali metals, alkaline earth metals, halogens, and noble gases share characteristic chemistry.

Elements have varying natural abundances; many are natural, while others are synthetic and produced in laboratories or reactors.

The most common elements in the Earth's crust include oxygen, silicon, aluminum, iron, calcium, and sodium, while hydrogen dominates the universe.

Isotopes are variants with different numbers of neutrons; some are stable, others radioactive.

Elements can exist in different allotropes, such as carbon as graphite and diamond, depending on structure.

Key properties include state of matter, conductivity, and reactivity, which depend on electron configuration and bonding.

Elements are the building blocks of all substances: through chemical bonds they form compounds and materials central to chemistry, biology, geology, and physics.