For a negative beta particle why is it that its mass number is 0 and its atomic number is -1 because if : mass number = num of (protons + neutrons) and atomic number= num of (protons) , why wouldn't the mass number be -1 aswell , I know the mass of an electron is 0 but if protons make up the mass and atomic numbers then why is just the atomic number -1?

  • $\begingroup$ The beta particle is an electron. $\endgroup$ – probably_someone Apr 18 '18 at 19:07
  • $\begingroup$ Yeah but what makes it's atomic number -1 , i'm sure it's the charge but why is the atomic number now charge ? $\endgroup$ – Fred Apr 18 '18 at 19:09
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    $\begingroup$ The atomic number was always charge. $\endgroup$ – probably_someone Apr 18 '18 at 19:09
  • $\begingroup$ I thought it was the total number of protons? $\endgroup$ – Fred Apr 18 '18 at 19:10
  • $\begingroup$ thats what I don't get why is it 0 over -1 ? $\endgroup$ – Fred Apr 18 '18 at 19:11

The so-called mass number is really a nucleon count, since the neutron's mass is very slightly more than the proton's, while the electron's is nearly 2000 times smaller. In fact, we can think of it more fundamentally as a conserved quantity called the baryon number (for which each nucleon scores 1, while the electron scores 0).

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    $\begingroup$ A related answer expands on baryon number as a conserved quantity, but also discusses some issues that are probably not yet useful to this asker. $\endgroup$ – rob Apr 18 '18 at 20:13

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