What is atomic weight?

What is atomic weight?

• A. Average of the mass numbers of all isotopes
• B. The number of protons in the nucleus
• C. The total number of electrons
• D. The mass number of the most abundant isotope

Answer: (A)

Atomic weight is the mass of an element as it occurs in nature, which comes from averaging the masses of its naturally occurring isotopes according to how abundant each isotope is. Since isotopes differ in neutron number, they have different masses, so the overall weight reflects a weighted average across those isotopes. In simple terms, you’re combining the mass numbers of all isotopes, weighted by how common each one is, to get the element’s average mass. The other options describe protons (atomic number), electrons (which can vary with charge), or the mass number of just the most abundant isotope, none of which capture the idea of averaging across all isotopes with their abundances.

Atomic weight is the mass of an element as it occurs in nature, which comes from averaging the masses of its naturally occurring isotopes according to how abundant each isotope is. Since isotopes differ in neutron number, they have different masses, so the overall weight reflects a weighted average across those isotopes. In simple terms, you’re combining the mass numbers of all isotopes, weighted by how common each one is, to get the element’s average mass. The other options describe protons (atomic number), electrons (which can vary with charge), or the mass number of just the most abundant isotope, none of which capture the idea of averaging across all isotopes with their abundances.