Atomic weight is defined as which of the following?

Atomic weight is defined as which of the following?

• A. Mass number
• B. Number of protons
• C. Average of all isotopes of an atom
• D. Charge

Answer: (C)

Atomic weight reflects the actual mass of a sample of an element, taking into account all the isotopes that occur naturally and how abundant each one is. It’s a weighted average of the masses of those isotopes, not a property of a single atom. That’s why the definition is the average of all isotopes, weighted by their natural abundances. The mass number describes just one isotope (protons plus neutrons), the number of protons is the atomic number, and the charge depends on the ionization state—none of these give the overall average mass of natural samples. In practice, the atomic weight is often given in atomic mass units or grams per mole and can be a non-integer because of the varying isotope mix.

Atomic weight reflects the actual mass of a sample of an element, taking into account all the isotopes that occur naturally and how abundant each one is. It’s a weighted average of the masses of those isotopes, not a property of a single atom. That’s why the definition is the average of all isotopes, weighted by their natural abundances. The mass number describes just one isotope (protons plus neutrons), the number of protons is the atomic number, and the charge depends on the ionization state—none of these give the overall average mass of natural samples. In practice, the atomic weight is often given in atomic mass units or grams per mole and can be a non-integer because of the varying isotope mix.