There are four basic quantum numbers to describe any electron in an atom.  The first three quantum numbers are the principal quantum number, the azimuthal quantum number, and the magnetic quantum number.  The principal quantum number denotes the energy shell level of the electron.  The azimuthal quantum number denotes the subshell of the electron.  These subshells have very specific shapes and as such they can determine the types of bonds the atom will be a part of and the reactivity of the bond.  Finally, the magnetic quantum number describes the specific orbital within the subshell that the electron occupies.