Mass number
The mass number is the number of protons plus the number of neutrons in the atom. It is always the biggest number and is roughly double the atomic number.
![The mass number is the protons plus neutrons, and is roughly double the atomic number](/images/user/base/Chemistry/2. Atomic Structure/2.2.11 Mass number memory aid (2).jpg)
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The mass number is the number of protons plus the number of neutrons in the atom. It is always the biggest number and is roughly double the atomic number.