Question

magnesium (mg) is in group 2 and period 3. how many energy levels (shells) does it have, and how many valence electrons?
2 energy levels, 2 valence electrons
2 energy levels, 8 valence electrons
3 energy levels, 2 valence electrons
3 energy levels, 8 valence electrons

Explanation:

Step1: Recall period - energy level relation

The period number of an element in the periodic table is equal to the number of energy levels (shells) it has. Magnesium is in period 3, so it has 3 energy levels.

Step2: Recall group - valence electron relation

The group number of a main - group element (groups 1 - 2 and 13 - 18) gives the number of valence electrons. Magnesium is in group 2, so it has 2 valence electrons.

Answer:

3 energy levels, 2 valence electrons (corresponds to the third option in the multiple - choice list)