Atomic mass refers to

Atomic mass refers to

• A. The number of protons plus the number of neutrons
• B. The number of electrons
• C. The number of electron shells
• D. The number of protons

Answer: (A)

Atomic mass is the total number of nucleons in the nucleus—the protons plus the neutrons. Mass mainly comes from these particles, while electrons are so light that their mass is negligible for this purpose. So the atomic mass essentially equals the mass number, the sum of protons and neutrons. The number of protons (the atomic number) defines the element, but not its mass. For example, carbon-12 has 6 protons and 6 neutrons, giving a mass of about 12 amu.

Atomic mass is the total number of nucleons in the nucleus—the protons plus the neutrons. Mass mainly comes from these particles, while electrons are so light that their mass is negligible for this purpose. So the atomic mass essentially equals the mass number, the sum of protons and neutrons. The number of protons (the atomic number) defines the element, but not its mass. For example, carbon-12 has 6 protons and 6 neutrons, giving a mass of about 12 amu.