To determine the valency of chlorine, sulfur, and magnesium, you need to find the number of electrons each atom needs to gain, lose, or share to achieve a stable electron configuration, typically a full outer shell with 8 electrons (octet rule).
Chlorine (Cl):
Electronic configuration: Chlorine has 17 electrons. Its electron configuration is 2, 8, 7.
Valency: To achieve a full outer shell, chlorine needs to gain one electron. Therefore, its valency is 1.
Sulfur (S):
Electronic configuration: Sulfur has 16 electrons. Its electron configuration is 2, 8, 6.
Valency: Sulfur needs to gain two electrons to complete its octet. Therefore, its valency is 2.
Magnesium (Mg):
Electronic configuration: Magnesium has 12 electrons. Its electron configuration is 2, 8, 2.
Valency: Magnesium can lose two electrons to achieve a full outer shell, making it a stable 8-electron configuration. Therefore, its valency is 2.