Draw the Lewis structure for SO32−, including lone pairs. Select Draw Rings More Erase Select Draw Rings More Erase Select Draw Rings More Erase Select Draw Rings More Erase S O What is the molecular shape of SO32−? bent trigonal pyramidal linear trigonal planar tetrahedral What is the O−S−O bond angle? 180∘ <109.5∘ 109.5∘ 120∘ The S−O bond in SO32− is The molecule SO32− is
The Correct Answer and Explanation is :
Lewis Structure of SO₃²⁻
To draw the Lewis structure of the sulfite ion (SO₃²⁻):
- Total valence electrons:
- Sulfur (S) has 6 valence electrons.
- Each oxygen (O) atom has 6 valence electrons, so for 3 oxygen atoms, that’s 18 electrons.
- The ion carries a 2− charge, meaning we add 2 more electrons to the total.
Total electrons: 6 (S) + 18 (O) + 2 (charge) = 26 electrons.
- Drawing the structure:
- Place sulfur in the center and arrange three oxygen atoms around it.
- Connect each oxygen to sulfur with a single bond. Each bond uses 2 electrons, so 3 bonds use 6 electrons.
- Distribute the remaining 20 electrons to satisfy the octet rule. Give each oxygen atom 6 electrons (3 lone pairs) and place a lone pair on the sulfur atom. After this, sulfur has 10 electrons (more than an octet) because it can expand its octet, being in Period 3 of the periodic table. However, the structure is stable with formal charges minimized by the arrangement.
Molecular Shape and Bond Angles
- Molecular shape:
The molecular shape of SO₃²⁻ is trigonal pyramidal. This is because the central sulfur atom is surrounded by three oxygen atoms and one lone pair. Lone pairs take up more space and repel the bonding pairs, resulting in this 3D shape. - Bond angles:
The ideal bond angle for a tetrahedral electron geometry is 109.5°, but due to the lone pair-bond pair repulsion, the O−S−O bond angles will be slightly less than 109.5°.
S−O Bond Characteristics and Molecular Polarity
- S−O bond:
The sulfur-oxygen bonds in SO₃²⁻ are polar due to the difference in electronegativity between sulfur and oxygen. However, the lone pair on sulfur adds asymmetry to the molecule. - Polarity:
SO₃²⁻ is a polar molecule because of its asymmetric shape, which leads to an unequal distribution of charge.