Question

determine the number of 3s electrons in mg. express your answer as an integer. part b determine the number of 3d electrons in cr. express your answer as an integer.

Explanation:

Step1: Determine electron configuration of Mg

Magnesium (Mg) has atomic number \( Z = 12 \). Using the Aufbau principle, the electron configuration is \( 1s^{2}2s^{2}2p^{6}3s^{2} \).

Step2: Count 3s electrons

From the electron configuration \( 1s^{2}2s^{2}2p^{6}3s^{2} \), the number of 3s electrons is 2.

Step3: Determine electron configuration of Cr

Chromium (Cr) has atomic number \( Z = 24 \). Due to the stability of half - filled orbitals, its electron configuration is \( 1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{1}3d^{5} \).

Step4: Count 3d electrons

From the electron configuration \( 1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{1}3d^{5} \), the number of 3d electrons is 5.

Answer:

For Mg: 2
For Cr: 5