photon and its wavelength. 9.10938291(40)×10 -31 The mass of an electron in kilograms, from CODATA 2010 values 50 . 1.672621777(74)×10 -27 The mass of a proton in kilograms, from CODATA 2010 values 50 . 1.674927351(74)×10 -27 The mass of a neutron in kilograms, from CODATA 2010 values 50 . 5.77×10 -24