Answers to GCSE Mass number and Atomic Number

Practice Questions

1. Using a periodic table, write down the mass number and atomic number of Fluorine. 

Mass number = 19

Atomic number = 9

If you do not have access to a periodic table, you can use the AQA one here

2. How many neutrons are in an atom of Phosphorous-31?

Mass number = 31

Atomic number = 15

Number of neutrons = mass number – atomic number 

Number of neutrons = 31-15 = 16

3. Explain why Aluminium atoms are electrically neutral

Each proton has a +1 charge and each electron has a -1 charge. An aluminium atom has 13 protons and 13 electrons, so the charges cancel out, it is electrically neutral