The electron is the lightest charged particle in an atom, about 1836 times lighter than a proton. That's why atomic mass is almost all in the nucleus.
Value of mₑ in different units
| Value | Use it when |
|---|---|
| 9.109 × 10⁻³¹ kg | SI. |
| 9.109 × 10⁻²⁸ g | CGS. |
| 5.486 × 10⁻⁴ u | About 1/1836 of a proton. |
| 0.511 MeV/c² | Rest energy, for nuclear and pair-production questions. |
Formulas that use mₑ
- λ = h/√(2mₑ·eV) for an accelerated electron
- rₙ = 0.529 n²/Z Å
- e/mₑ = 1.76 × 10¹¹ C/kg
Other constants
- Gas constant (R): 8.314 J mol⁻¹ K⁻¹
- Planck's constant (h): 6.626 × 10⁻³⁴ J s
- Avogadro's number (Nₐ): 6.022 × 10²³ mol⁻¹
- Speed of light (c): 3 × 10⁸ m/s
- Charge of an electron (e): 1.602 × 10⁻¹⁹ C
- Mass of an electron (mₑ): 9.109 × 10⁻³¹ kg
- Mass of a proton (mₚ): 1.673 × 10⁻²⁷ kg
- Mass of a neutron (mₙ): 1.675 × 10⁻²⁷ kg
- Universal gravitational constant (G): 6.674 × 10⁻¹¹ N m² kg⁻²
- Acceleration due to gravity (g): 9.8 m/s²
- Boltzmann constant (k): 1.381 × 10⁻²³ J/K
- Faraday constant (F): 96 485 C/mol
- Permittivity of free space (ε₀): 8.854 × 10⁻¹² C² N⁻¹ m⁻²
- Permeability of free space (μ₀): 4π × 10⁻⁷ T m/A
- Rydberg constant (R): 1.097 × 10⁷ m⁻¹
- Stefan–Boltzmann constant (σ): 5.67 × 10⁻⁸ W m⁻² K⁻⁴
- Wien's constant (b): 2.898 × 10⁻³ m K
- Bohr radius (a₀): 0.529 Å
- Molar volume of a gas at STP (Vₘ): 22.4 L/mol
The full list, searchable, is on the physical constants page.
Questions students ask
What is the value of mass of an electron?
mₑ = 9.109 × 10⁻³¹ kg. In other units: 9.109 × 10⁻³¹ kg; 9.109 × 10⁻²⁸ g; 5.486 × 10⁻⁴ u; 0.511 MeV/c².
What is mₑ in physics and chemistry?
The electron is the lightest charged particle in an atom, about 1836 times lighter than a proton. That's why atomic mass is almost all in the nucleus.
Which value of mₑ should I use?
9.109 × 10⁻³¹ kg: SI. 9.109 × 10⁻²⁸ g: CGS. 5.486 × 10⁻⁴ u: About 1/1836 of a proton. 0.511 MeV/c²: Rest energy, for nuclear and pair-production questions.