Electrons are the smallest parts of the atom. They are the most numerous of the three. It has no known components or substructure, so it is an elementary particle. Its mass is 1/1836 of a proton. It is also considered to be a fermion. It has an antiparticle called the positron. The positron is identical to the electron except that it carries opposite charge. When an electron collides with a positron, both particles will either scatter or be destroyed producing gamma ray photons. Electrons can collide with other particles and be diffracted like light. Two electrons can not occupy the same quantum state based on the Pauli exclusion principle.
The proton is the part of an atom that helps to form the nucleus and has a positive charge. Protons must have an equal number of neutrons except int eh hydrogen atom where a single proton exists on its own. A proton is composed of 2 up quarks and one down quark. They are considered to be fermions and baryons. They are held together by the strong nuclear force. The number of protons in the nucleus of an atom determines the atomic number.
A neutron is the part of an atom that holds no charge. Neutrons and protons occur in equal numbers in stable atoms except in hydrogen. Protons and neutrons are often referred to together as nucleons. If there are more neutrons than protons, then the atom is considered an isotope. If an neutron becomes free of its proton, then it becomes unstable, undergoes beta decay, and will disintegrate in an average of 15 minutes. The neutron is also important in nuclear chain reactions: both natural and artificial.
This is only meant to be a basic introduction of the parts of an atom. With additional research you may find yourself immersed for hours in just the introduction to the world of the atom.
If you’d like more info on the atom, check out NASA’s Article on Analyzing Tiny Samples, and here’s a link to NASA’s Article about Atoms, Elements, and Isotopes.
We’ve also recorded an entire episode of Astronomy Cast all about the Atom. Listen here, Episode 164: Inside the Atom.