Electrons (symbol: e) are subatomic particles with a negative elementary electric charge.

 Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no known components or substructure.

The electron has a mass that is approximately 1/1836 that of the proton. Quantum mechanical properties of the electron include an intrinsic angular momentum (spin) of a half-integer value in units of ħ, which means that it is a fermion.

Being fermions, no two electrons can occupy the same quantum state, in accordance with the Pauli exclusion principle.

Electrons also have properties of both particles and waves, and so can collide with other particles and can be diffracted like light. Experiments with electrons best demonstrate this duality because electrons have a tiny mass.                                                                

note: There is no picture of an electron because you can't really 'see' an electron.

mass of electron is 0.5109989461(31) MeV/c2

source: http://en.wikipedia.org/wiki/Electron