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Magnesium is an alkaline earth metal with an atomic number of 12. It’s in the third row in the periodic table. Which expression shows one way to find the number of valence electrons in one atom of magnesium?
12 × 3
12 ÷ 3
(12 − 8) − 2
(12 − 2) + 8
(12 + 2) − 8
Magnesium is an alkaline earth metal with an atomic number of 12. It’s in the third row in the periodic table. Which expression shows one way to find the number of valence electrons in one atom of magnesium?
12 × 3
12 ÷ 3
(12 − 8) − 2
(12 − 2) + 8
(12 + 2) − 8
1 Answer
The number of valence electrons in one atom of magnesium is (12 − 8) − 2.
Explanation:
Magnesium is in the third row of the Periodic Table. It has 12 electrons.
Row 1 has two elements, and Row 2 has eight.
Each element has one more electron than the element preceding it.
The eight valence electrons in Group 2 are "core electrons" (inside the valence electrons) of Group 3 elements.
Subtracting these gives us (12 - 8) electrons.
However, the valence electrons in Group 1 are also core electrons of Group 3 elements.
We must subtract these electrons in magnesium.
(12 - 8) - 2 = 2
Thus, an atom of magnesium has ten core electrons and two valence electrons.
