Atomic Structure
Atomic and Mass Number
To use atomic number and mass number to work out the numbers of protons, neutrons and electrons in atoms.
What you will learn
What atomic number tells you about an element
What mass number tells you about a nucleus
How to work out the number of protons
How to calculate neutron and electron numbers
How to read atomic and mass number notation
Explanation
Atomic number is the number of protons and identifies the element. Mass number is the total number of protons and neutrons. Subtract atomic number from mass number to find neutrons; a neutral atom has the same number of electrons as protons. Example: A neutral atom has atomic number 8 and mass number 19. Determine its neutron number. Neutrons = A − Z = 19 − 8 = 11. It also has 8 protons and 8 electrons. A correct answer needs an appropriate unit as well as a numerical value. Justify your answer.