• Question: How much to protons, neutrons and electrons weigh? (Not in relative mass)

    Asked by crouchingmurloc to Ed on 18 Jun 2013.
    • Photo: Ed Lowe

      Ed Lowe answered on 18 Jun 2013:

      If you’re happy with a first approximation, you can work it out! If we start out by assuming that protons and neutrons weigh the same and electons are weightless (none of these are true, but are very, very close to true) then we can say that all the mas of a hydrogen atom is a due to its single proton. A mole of hydrogen weighs 1g and contains Avogardro’s number (6×10^23, roughly) of atoms. This means that a single proton (or neutron) weighs roughly 1/(6×10^23) grammes, or 1.6×10^-27 kg in SI units, which is a very small number indeed!
      The textbook values are:
      proton: 1.672621777 ×10−27 kg
      neutron: 1.674927351 ×10−27 kg
      electron: 9.10938291 ×10−31 kg (more than 1000 times lighter than a proton!)

      So we weren’t too far out and it’s more fun to work it out.

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