Answer
Magnesium (Mg): $ 1s^2 \, 2s^2 \, 2p^6 \, 3s^2 $
Strontium (Sr): $ 1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 4s^2 \, 3d^{10} \, 4p^6 \, 5s^2 $
Barium (Ba): $ 1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 4s^2 \, 3d^{10} \, 4p^6 \, 5s^2 \, 4d^{10} \, 5p^6 \, 6s^2 $
Work Step by Step
Let's predict the ground-state electron configurations for $\bf Magnesium (Mg)$:
The atomic number is 12.
Electron Configuration: The first 2 electrons will fill the 1s orbital, the next 2 will fill the 2s orbital, the next 6 will fill the 2p orbital, and the final 2 will occupy the 3s orbital.
Thus, the ground-state configuration of Mg is
$$
\boxed{ \text{Mg}: 1s^2 \, 2s^2 \, 2p^6 \, 3s^2}
$$
Let's predict the ground-state electron configurations for $\bf Strontium (Sr)$:
The atomic number is 38.
Electron Configuration: Following the filling order, the configuration will fill up to 4p and then 5s.
Thus, the ground-state configuration of Sr is
$$
\boxed{ \;\; \text{Sr}: 1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 4s^2 \, 3d^{10} \, 4p^6 \, 5s^2\;\;}
$$
Let's predict the ground-state electron configurations for $\bf Barium (Ba)$:
The atomic number is 56.
Electron Configuration: The configuration will fill up to 5p and then 6s.
Thus, the ground-state configuration of Ba is
$$
\boxed{ \;\; \text{Ba}: 1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 4s^2 \, 3d^{10} \, 4p^6 \, 5s^2 \, 4d^{10} \, 5p^6 \, 6s^2\;\;}
$$
