valence electron(n = noun.object) - an electron in the outer shell of an atom which can combine with other atoms to form molecules;
is a kind of electron, negatron

electron, electron accelerator, electron beam, electron emission, electron gun, electron lens, electron microscope, electron microscopic, electron microscopy, electron multiplier, electron optics, electron orbit, electron paramagnetic resonance, electron radiation, electron shell, electron spin resonance, electron tube, electron volt, free electron, valence