Atomic mass more significant figures than atomic weights. Standard atomic weight is related to atomic mass by the abundance ranking of isotopes for each element. It is usually "about" the same value as the atomic mass of the most abundant isotope, other than what looks like (but is not actually) a rounding difference. The atomic mass of atoms, ions, or atomic nuclei is slightly less than the sum of the masses of their constituent protons, neutrons, and electrons, due to binding energy mass loss (as per "E"="mc"). Relative "isotopic" mass (a property of a single atom) is not to be confused with
Avoided crossing one set of parameters. If both of the atoms of a diatomic molecule is same, the symmetry suggests that different configurations keeping their mutual distance fixed will result into same electronic states. So it is the relative distance formula_73 which acts as a parameter for the two equations promising level crossing. Hence due to the avoided crossing theorem in general we can not have level crossings between two electronic states of same symmetry. But in polyatomic molecules the number of independent mutual distances of nuclei are more. For a N-atomic molecule the number of independent mutual separation is formula_74 (for