Answer
The two extra electrons in the sulfite ion, SO$_3^{2–}$, cause its shape to be different from the SO$_{3}$ molecule. The SO$_3^{2–}$ ion is trigonal pyramidal with 4 regions of high electron density, whereas the SO$_{3}$ molecule is trigonal planar.
Work Step by Step
The two extra electrons in the sulfite ion, SO$_3^{2–}$, cause its shape to be different from the SO$_{3}$ molecule. The SO$_3^{2–}$ ion is trigonal pyramidal with 4 regions of high electron density, whereas the SO$_{3}$ molecule is trigonal planar.