The atom’s mass is about 15 atomic mass units (amu).

Quick Scoop

  • Protons and neutrons each have a mass of roughly 1 amu.
  • Mass number ≈ protons + neutrons = 7+7=147+7=147+7=14 if you use the numbers in your text, or 7+8=157+8=157+8=15 for the common nitrogen‑15 case often discussed in class.
  • Because electrons are so light, their total mass barely changes the result.

In school chemistry, when someone asks “what is the mass of an atom with seven protons, seven neutrons, and eight electrons?” , they almost always want the mass number , so you add protons and neutrons and get 14–15 amu depending on the exact neutron count assumed.

Bottom line: if the nucleus has 7 protons and 7 neutrons, use 14 amu ; if it’s the usual nitrogen‑15 example with 7 protons and 8 neutrons, it’s 15 amu.

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