What is the valency of Magnesium with atomic number 12?

• A. 2
• B. 4
• C. 6
• D. 5

To determine the valency of magnesium, we first need to understand its position in the periodic table and its electron configuration. Magnesium has an atomic number of 12, which means it has 12 protons and, in a neutral atom, also 12 electrons. The electron configuration of magnesium is 1s² 2s² 2p⁶ 3s². This configuration shows that magnesium has two electrons in its outermost shell, which is the third energy level (3s²).

Understanding Valency

Valency refers to the ability of an atom to bond with other atoms, which is determined by the number of electrons in its outer shell. Atoms tend to be more stable when they have a full outer shell, typically consisting of eight electrons, known as the octet rule. However, some elements, like magnesium, can achieve stability by losing or gaining electrons.

Magnesium's Electron Configuration

In the case of magnesium, it has two electrons in its outermost shell. To achieve a stable electron configuration, magnesium can lose these two electrons. By losing these two electrons, magnesium achieves the electron configuration of neon, a noble gas, which is stable due to having a full outer shell.

Determining Valency

Since magnesium can lose two electrons to achieve stability, its valency is 2. This means magnesium typically forms compounds by losing two electrons, resulting in a +2 charge. For example, in magnesium oxide (MgO), magnesium donates its two outer electrons to oxygen, which needs two electrons to fill its outer shell.

Conclusion

Given the options provided, the correct answer is A. 2. Magnesium's ability to lose two electrons and form a +2 ion is what defines its valency. This property is crucial in understanding how magnesium interacts with other elements and compounds in various chemical reactions.