Mass number

  • #1

Homework Statement

My instructor give me a question:
Mass number (number of protons and number of neutrons in an atom) is supposed to be a whole number for a particular atom, in reality IT IS NOT. Why is it so?

Homework Equations

The Attempt at a Solution

Here, I am very sure that this question ask for mass number (nucleon number) not atomic weight. However, how can only a part of a proton or neutron exist in an atom if mass number are not a whole number?
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Answers and Replies

  • #2
Staff Emeritus
Science Advisor
Homework Helper
Hint: Check out isotopes.
  • #3
you are absolutely correct. Mass number is the NUMBER of neutrons and protons (nucleons)
This does not mean that the MASS is a whole number.
Like steamking I suggest you look at isotopes to get the idea of mass

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