The wavelength of the electrons λ λ in vacuum is from the above equations λ λ = 1 k = h 2 m ∗ ∗ E = h c E ( 2 m 0 c 2 + E ) , and can range from about 0.1 nanometers, roughly the size of an atom, down to a thousandth of that. Typically the energy of the electrons is written in electronvolts (eV), the voltage used to accelerate the electrons; the actual energy of each electron is this voltage times the electron charge. For context, the typical energy of a chemical bond is a few eV; electron diffraction involves electrons up to 5,000,000 eV.