Question 7
Magnesium has atomic number 12, so its configuration is 2, 8, 2. Where does it sit in the periodic table?
The right answer is the one marked above.
Period 3, group II.
- Electrons occupy 3 energy levels → period 3.
- The last level holds 2 electrons → group II.
The atomic number itself is never the period or the group — 12 is simply how many electrons there are to place. Everything else is read off the configuration once you have written it.