-the basic building block of all matter
- made up of protons, neutrons, and electrons.
substance made entirely of one type of atom
a group of two or more atoms that are joined together.
Special type of molecule
- Made up of two or more elements.
tells you how many protons and electrons are in an atom
-the number of protons + the number of neutrons
Found inside the nucleus of an atom.
# of neutrons = (atomic number) - (number of protons)