Stoichiometry, Moles, and Molecular Weight

 Atoms are made up of protons (positive), neutrons (neutral), and electrons (negative).  The nucleus (center) of an atom contains the protons and neutrons, whereas the electrons are scattered away from the nucleus.  An element is a substance whose atoms all have the same atomic number (have the same number of protons).  The arrangement of a particular nucleus for a given element is called a nuclide, and nuclides are often expressed in the following way: