We learned before about how small atoms are,
but there are even things smaller that that!
An atom is really made up of two parts.
The nucleus in the middle, and the electrons that spin around the nucleus.
(from: wikipedia - atom)
The nucleus can be made up of two types of things, protons and neutrons.
Remember we've talked about positive and negative?
The electrons have negative charges, the protons have positive charges,
and the neutrons have no charge at all.