* Protons: These particles have a positive charge and are located in the atom's nucleus. The number of protons in an atom defines its atomic number and determines what element it is.

* Neutrons: These particles have no charge (they are neutral) and are also located in the atom's nucleus. Along with protons, they make up the majority of an atom's mass.

* Electrons: These particles have a negative charge and orbit the nucleus in specific energy levels called electron shells. The number of electrons in an atom is usually equal to the number of protons, giving the atom an overall neutral charge.

It's important to note that there are other, more exotic subatomic particles that can be found within atoms, but these are not as fundamental as the three mentioned above.