How to find the mass number of an atom?

The hydrogen atom may contain a neutron, but it usually doesn't, so the mass number of hydrogen is 1. Oxygen, on the other hand, has an equal number of proteins and neutrons, which raises its mass number to 16. Subtracting an element's mass number from its atomic mass tells you the number of protons in its nucleus. read more

The atomic mass of the atom is the mass of the protons plus the mass of the neutrons, 6 + 7, or 13. 3) Weighted Average for All Atoms of an Element. The atomic mass of an element is a weighted average of all the element's isotopes based on their natural abundance. It is simple to calculate the atomic mass of an element with these steps. read more

Therefore, to find the number of neutrons of sodium, subtract sodium's number of protons, which is 11, from its atomic weight, which is 23. Sodium's number of neutrons is 12. Add neutrons and protons together. Add the number of neutrons and protons together. The sum of these two values is the mass number. Thus, sodium's mass number is 23. read more