Neutrons are the other principal component of the nucleus of an atom (along with protons). The neutron is neutral in charge and has a mass roughly similar to that of a proton. Atoms of the same element that contain different numbers of neutrons will generally still have the same behavior as one another in terms of chemical reactivity properties. Both protons and neutrons are, in fact, made up of even smaller particles, but chemistry doesn’t usually deal with these even smaller bits.