Atomic mass?

Atomic mass?

• A. The total number of electrons in the atom
• B. The number of protons in the nucleus of an atom
• C. Number of protons and neutrons in the nucleus of an atom
• D. The mass of the atom

Answer: (C)

Atomic mass is determined by the particles in the nucleus—the protons and neutrons. The mass number, which defines atomic mass in a single isotope, is simply the sum of protons and neutrons. Electrons contribute very little to the overall mass, so they’re not what’s counted when we talk about atomic mass. That’s why the best description is the number of protons and neutrons in the nucleus. The other ideas aren’t right because the total number of electrons doesn’t reflect mass, protons alone don’t account for the entire nuclear mass, and “the mass of the atom” is a vague phrase that can imply electrons and binding energy rather than just the nucleons.

Atomic mass is determined by the particles in the nucleus—the protons and neutrons. The mass number, which defines atomic mass in a single isotope, is simply the sum of protons and neutrons. Electrons contribute very little to the overall mass, so they’re not what’s counted when we talk about atomic mass. That’s why the best description is the number of protons and neutrons in the nucleus.

The other ideas aren’t right because the total number of electrons doesn’t reflect mass, protons alone don’t account for the entire nuclear mass, and “the mass of the atom” is a vague phrase that can imply electrons and binding energy rather than just the nucleons.