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Atomic Structure and Electron Configuration

AP Chemistry· difficulty 4/5

The electron configuration of Fe3+\text{Fe}^{3+} (Z=26) is

  • A

    [Ar] 3d5[Ar]\,3d^5

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  • B

    [Ar] 3d4 4s1[Ar]\,3d^4\,4s^1

  • C

    [Ar] 3d3 4s2[Ar]\,3d^3\,4s^2

  • D

    [Ar] 3d6 4s0[Ar]\,3d^6\,4s^0

Explanation

Fe is [Ar] 3d6 4s2[Ar]\,3d^6\,4s^2. When ionizing, 4s electrons leave first: Fe2+\text{Fe}^{2+} is [Ar] 3d6[Ar]\,3d^6, Fe3+\text{Fe}^{3+} is [Ar] 3d5[Ar]\,3d^5 (the half-filled stability further favors this).

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