Remember that the number of electrons are equal to the number of protons, and to find the number of protons you have to look and see the atomic mass of the atom is equal to the number of protons, and to find the number of neutrons you have too subtract the atomic mass to the atomic number.
Example:
You want to find out how many protons, neutrons, and electrons are in Platinum:
- Atomic number is equal to the number of protons:
- So platinum has 78 protons and electrons.
- Subtract atomic mass to atomic number:
(forgetting about the decimals)
So platinum has "78 protons, and electrons, and has 117 neutrons."
Hope this helps!