Electron: definition in chemistry
Electron: A tiny subatomic particle with a negative electric charge (−1) that occupies the space around an atom's nucleus.
Electrons have only about 1/1836 of the mass of a proton, so they add almost nothing to an atom's mass, but they control its chemistry. Bonds form when atoms transfer or share electrons, and an electric current in a metal is a flow of electrons. The electron was discovered in 1897 by the British physicist J. J. Thomson.
Examples
- Hydrogen atoms have 1 electron; uranium atoms have 92
- Sodium loses one electron to form Na⁺
- Electric current in a copper wire is a flow of electrons
- Beta particles are fast electrons given off by some unstable nuclei
On the periodic table
An element's atomic number equals the number of electrons in its neutral atom, and its position on the table shows how those electrons are arranged.