1. Start with the neutral atom:
* Arsenic (As) has an atomic number of 33, meaning it has 33 protons and 33 electrons in its neutral state.
2. Determine the electron configuration of neutral arsenic:
* 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p³
3. Account for the negative charge:
* The As³⁻ ion has gained three electrons. These electrons will fill the 4p orbitals, which are the highest energy orbitals not completely filled in the neutral atom.
4. Final electron configuration of As³⁻:
* 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶
