What is the electron configuration of a Mg2+ ion?

What is the electron configuration of a Mg2+ ion?

• A. [Ne] 3s2
• B. [Ne] (1s2 2s2 2p6)
• C. [Ar]
• D. [He] 2s2

Answer: (B)

The main idea is how ions reach a stable electron arrangement by losing electrons from the outer shell. Magnesium in its neutral state has the configuration 1s2 2s2 2p6 3s2. To form Mg2+, it loses the two electrons in the outer 3s orbital, leaving 1s2 2s2 2p6. That set of electrons is exactly the configuration of the noble gas neon, often written as [Ne]. So Mg2+ is [Ne], or equivalently [Ne] (1s2 2s2 2p6). The other possibilities describe either the neutral magnesium or a larger atom, which don’t match the ion in question.

The main idea is how ions reach a stable electron arrangement by losing electrons from the outer shell. Magnesium in its neutral state has the configuration 1s2 2s2 2p6 3s2. To form Mg2+, it loses the two electrons in the outer 3s orbital, leaving 1s2 2s2 2p6. That set of electrons is exactly the configuration of the noble gas neon, often written as [Ne]. So Mg2+ is [Ne], or equivalently [Ne] (1s2 2s2 2p6). The other possibilities describe either the neutral magnesium or a larger atom, which don’t match the ion in question.