Themes > Science > Physics > Atomic Physics > Atomic Structure > New System of the Atom > Particle Classification > Atomic Weight (Mass Number) and Atomic Number

Mass number would now become merely the number of neutrons. Previously, it was protons plus neutrons. But "protons" are decayed neutrons. What we previously called "neutrons" are undecayed neutrons. This makes mass number the total of decayed and undecayed neutrons, or just the total number of neutrons.

Atomic number was protons or electrons, which were numerically the same. Now, it can’t be protons because they’re not fundamental particles. It’s just electrons, as before.

    MASS NUMBER
    Old system: protons plus neutrons
    New system: neutrons

    ATOMIC NUMBER
    Old system: protons or electrons
    New system: electrons

Thus, for example, the standard symbol for sodium:

    11 Na 23

tells us the nucleus is made up of 23 neutrons, of which 11 are decayed.

This means there are 11 electrons, or negative charges, spreading out from the nucleus, and 11 anti-electrons, or positive charges, inside the decayed neutrons, making them "protons."

For comparison, helium is 2 He 4 , meaning the nucleus is made up of 4 neutrons, of which 2 are decayed.

Uranium is 92 U 238 , meaning the nucleus is made up of 238 neutrons, of which 92 are decayed.


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