Electron rest mass
The electron rest mass (symbol: me) is the mass of a stationary electron. It is one of the fundamental constants of physics, and is also very important in chemistry because of its relation to the Avogadro constant. It has a value of about 9.11×10 kilograms or about 5.486×10 atomic mass units, equivalent to an energy of about 8.19×10 joules or about 0.511 megaelectronvolts.