Question

18 core electrons
8 valence electrons
argon (ar): ne 3s²3p⁶
10 core electrons
8 valence electrons
magnesium (mg): 1s²2s²2p⁶3s²
core electrons
valence electrons

Explanation:

Step1: Identify core electrons

Core electrons are the electrons in all but the out - most shell. For Mg with electron configuration $1s^{2}2s^{2}2p^{6}3s^{2}$, the electrons in $1s^{2}2s^{2}2p^{6}$ are core electrons. Calculate the number of core electrons: $2 + 2+6=10$.

Step2: Identify valence electrons

Valence electrons are the electrons in the out - most shell. For Mg, the out - most shell is the 3rd shell with electron configuration $3s^{2}$, so the number of valence electrons is 2.

Answer:

Core electrons: 10
Valence electrons: 2