Separate Mass Number from Atomic Number - Practice 1

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Mass number is the number of protons plus neutrons in a particular nucleus. Subtract atomic number, the proton count, to find neutrons. Mass number is an integer count, not the average atomic mass printed on many periodic tables.

Worked example

A nucleus with mass number 23 and atomic number 11 has 23 - 11 = 12 neutrons.

A nucleus count model labels 6 protons P and 7 neutrons N. Atomic number is 6; mass number is 13. Electrons are omitted and the layout is not a physical scale model.

Question 1 A model isotope has atomic number 5 and mass number 12. How many neutrons are in its nucleus? Answer

Question 2 A model isotope has atomic number 6 and mass number 14. How many neutrons are in its nucleus? Answer

Question 3 A model isotope has atomic number 7 and mass number 16. How many neutrons are in its nucleus? Answer

Question 4 A model isotope has atomic number 8 and mass number 18. How many neutrons are in its nucleus? Answer

Question 5 A model isotope has atomic number 9 and mass number 20. How many neutrons are in its nucleus? Answer