Atomic weight
From Encyclopædia
Atomic weight is the
average Mass of
atoms of an element relative to some standard; the present standard is the
carbon-12 isotope, which is assigned an atomic weight of exactly 12 atomic
Mass units (amu).
Mass numbers (the sum of an
atom's protons and
neutrons) are always whole
numbers, but the atomic weight of an element is the
average of the weights of its ISOTOPES, taking the
frequency of their natural occurrence into account, and is not usually a whole
number. A gram atomic weight is a quantity of an element in grams that has the same numerical value as the element's atomic weight; the gram atomic weight of
carbon, for example, is 12 grams. Such a quantity always contains 6.022X(10 to the power of 23)
atoms (one mole). For the atomic weights of the elements, see
periodic table.
