Mn II (Manganese(II) ion) possesses an electron configuration of 3d⁵. This specific configuration arises from the way electrons are organized in neutral manganese and subsequently lost during the ionization process to form the Mn²⁺ cation.
Understanding Manganese's Electron Configuration
To comprehend why Mn II is 3d⁵, we first need to look at the electron configuration of a neutral manganese atom (Mn), which has an atomic number of 25.
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Neutral Manganese (Mn): The electron configuration for a neutral manganese atom is
[Ar] 3d⁵ 4s². This means it has the core electron configuration of Argon, followed by five electrons in the 3d subshell and two electrons in the 4s subshell.- The (n+l) Rule: The filling order of electron shells and subshells in neutral atoms is often determined by the (n+l) rule, where 'n' is the principal quantum number and 'l' is the azimuthal quantum number. Lower (n+l) values indicate lower energy.
- For 4s: n=4, l=0; (n+l) = 4+0 = 4
- For 3d: n=3, l=2; (n+l) = 3+2 = 5
- Based on this rule, the 4s subshell has a lower energy than the 3d subshell, which is why the 4s orbital is filled with electrons before the 3d orbital in neutral manganese atoms.
- The (n+l) Rule: The filling order of electron shells and subshells in neutral atoms is often determined by the (n+l) rule, where 'n' is the principal quantum number and 'l' is the azimuthal quantum number. Lower (n+l) values indicate lower energy.
Formation of the Mn(II) Ion
When a neutral atom forms a cation (a positively charged ion), it loses electrons. For transition metals like manganese, there's a specific pattern for electron removal:
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Electron Ejection from the Outermost Subshell: When manganese forms a +2 ion (Mn²⁺), it loses two electrons. Although the 3d subshell is filled after the 4s subshell in neutral manganese due to the (n+l) rule, the 4s subshell electrons are actually in the outermost principal energy level (n=4) compared to the 3d subshell (n=3). Consequently, the electrons with the highest principal quantum number are the first to be removed during ionization.
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Loss of 4s Electrons: Therefore, the two electrons in the 4s subshell are the first to be ejected from the manganese atom.
- Neutral Mn:
[Ar] 3d⁵ 4s² - Mn²⁺ formation: Removes two electrons from
4s² - Resulting Mn²⁺:
[Ar] 3d⁵ 4s⁰(or simply[Ar] 3d⁵)
- Neutral Mn:
Why 3d⁵ is Stable
The resulting 3d⁵ electron configuration for Mn²⁺ is particularly stable. According to Hund's Rule and the principles of quantum mechanics, a half-filled subshell (like 3d⁵, where each of the five d orbitals contains one electron) exhibits extra stability due to:
- Symmetry: A half-filled subshell is highly symmetrical.
- Exchange Energy: All electrons in a half-filled subshell have parallel spins, leading to maximum exchange energy, which contributes to increased stability.
This enhanced stability is a significant factor in why Mn²⁺ is a common and stable ion for manganese.
Summary of Electron Configurations
| Species | Atomic Number | Electron Configuration | Key Characteristic |
|---|---|---|---|
| Neutral Mn | 25 | [Ar] 3d⁵ 4s² |
4s filled before 3d |
| Mn(II) Ion | 25 | [Ar] 3d⁵ |
4s electrons removed, 3d⁵ stable |
For further reading on electron configurations and the (n+l) rule, you can explore resources like LibreTexts Chemistry.
