Question

use the periodic table to identify the number of core electrons and the number of valence electrons in each case below.
potassium (k): 1s²2s²2p⁶3s²3p⁶4s¹
argon (ar): ne3s²3p⁶
18 √ core electrons
1 √ valence electrons
complete
10 √ core electrons
8 √ valence electrons
complete
iron (fe): ar4s²3d⁶
magnesium (mg): 1s²2s²2p⁶3s²
18 √ core electrons
8 √ valence electrons
complete
core electrons
valence electrons
done √

Explanation:

Step1: Recall electron - configuration rules

Core electrons are inner - shell electrons, and valence electrons are outer - shell electrons.

Step2: Analyze magnesium's electron configuration

Magnesium (Mg) has an electron configuration of $1s^{2}2s^{2}2p^{6}3s^{2}$. The noble - gas core equivalent to neon is $1s^{2}2s^{2}2p^{6}$, which has 10 electrons. These are the core electrons.

Step3: Determine valence electrons

The electrons in the outermost shell (n = 3 for Mg) are the valence electrons. In the $3s^{2}$ sub - shell, there are 2 valence electrons.

Answer:

10 core electrons
2 valence electrons