Electron

An electron is a fundamental particle carrying negative electric charge. It is one of the three most important components of atomic structure, along with the proton (positively charged) and the neutron (uncharged). Electrons orbit the nucleus of an atom in a structured energy level system.

The electron mass is extremely small compared to that of a proton—roughly more than a thousand times lighter. For this reason, most of an atom's mass resides in the nucleus, while electrons determine the atom's size and how it interacts with other atoms.

Basic properties

The electron is a lepton—a class of particles that do not participate in the strong nuclear force. As far as modern physics knows, the electron has no smaller constituent parts and is therefore considered a fundamental particle. It possesses a property called spin, with a value of one-half, making it a type of particle known as a fermion. Fermions obey the Pauli exclusion principle, which states that no two electrons can occupy the same quantum state within the same atom.

Role in chemistry and electricity

Chemical changes depend largely on how electrons in the outer shell of an atom are transferred or shared. Ionic bonding results from electron transfer, while covalent bonding results from electron sharing. Similarly, electric current in metal circuits consists of the flow of free electrons moving through the metal.

Wave and particle nature

The electron exhibits both particle and wave properties. Diffraction experiments showed that electrons behave like waves when passing through very small openings. This observation underlies quantum physics and is applied in devices such as the electron microscope, which uses electrons instead of light to image extremely small objects.

Positron

Every electron has an opposite counterpart called a positron, which has the same mass but positive charge. When an electron and positron meet, they annihilate each other and convert into light energy (photons). The positron has medical applications in PET imaging.