What is mass number equal to?

Answer 1

The total number of nucleons - protons and neutrons - in the nucleus of an atom is called the Mass Number.

For example, the most common isotope of fluorine has an atomic number of 9 and a mass number of 19.

The atomic number tells us there are 9 protons in the nucleus (and also 9 electrons in the shells surrounding the nucleus).

The mass number tells us the nucleus contains 19 particles in total. Since 9 of these are protons, the other 10 are neutrons. We call it the mass number because virtually all the mass in an atom comes from the protons and neutrons - electrons weigh about 1/2000th of the mass of a proton or neutron.

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Answer 2

Noah Aldrich

The mass number is equal to the total number of protons and neutrons in an atomic nucleus.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.