To determine the number of valence electrons in an atom of magnesium, we need to understand magnesium’s electron configuration. Magnesium (Mg) has an atomic number of 12, meaning it has 12 electrons. It is also known to be in the third period of the periodic table and belongs to the group of alkaline earth metals. Alkaline earth metals characteristically have 2 valence electrons.
Let's break down the possible electron configuration for magnesium:
- The first energy level can hold up to 2 electrons.
- The second energy level can hold up to 8 electrons.
- The third energy level, where the valence electrons reside for magnesium, would hold the remaining electrons.
Since magnesium has 12 electrons:
- Filling the first shell: 2 electrons
- Filling the second shell: 8 electrons
- The remaining electrons go into the third shell, which would be: 2 electrons
Thus, the electron configuration of magnesium (Mg) is 2, 8, 2. Therefore, it has 2 valence electrons.
We need to find the expression that correctly calculates the number of valence electrons, 2. Let's analyze each given option:
A. [tex]\(12 \times 3 = 36\)[/tex]
The product does not match the number of valence electrons (2).
B. [tex]\(12 \div 3 = 4\)[/tex]
The quotient does not match the number of valence electrons (2).
C. [tex]\((12 - 8) - 2\)[/tex]
This expression simplifies as follows:
[tex]\[
12 - 8 = 4 \quad \text{and} \quad 4 - 2 = 2
\][/tex]
This correctly gives us the number of valence electrons (2).
D. [tex]\((12 - 2) + 8\)[/tex]
This expression simplifies as follows:
[tex]\[
12 - 2 = 10 \quad \text{and} \quad 10 + 8 = 18
\][/tex]
The sum does not match the number of valence electrons (2).
E. [tex]\((12 + 2) - 8\)[/tex]
This expression simplifies as follows:
[tex]\[
12 + 2 = 14 \quad \text{and} \quad 14 - 8 = 6
\][/tex]
The difference does not match the number of valence electrons (2).
Through the process of elimination and correct calculation, option C [tex]\((12 - 8) - 2\)[/tex] accurately provides the correct result for the number of valence electrons in one atom of magnesium. Thus, the correct answer is:
C. [tex]\((12 - 8) - 2\)[/tex]
