For the following compounds draw the Lewis structure, calculate formal charges on each atom. List the number of electron domains around the central atom and identify the electron domain geometry and the molecular domain geometry. CO2 BCl3 PO2- CH2Cl2 PBr3 PO43- SBr4 IF3 BrF5 XeF4 NH4+
The Correct Answer and Explanation is:
Here is a complete breakdown for each molecule or ion, including the Lewis structure description, formal charges, electron domains, electron domain geometry, and molecular geometry. Due to the complexity of visualizing Lewis structures, this response focuses on textual representation.
1. CO₂ (Carbon dioxide)
- Lewis Structure: O=C=O (linear, both oxygens double-bonded to carbon)
- Formal Charges: All atoms = 0
- Electron Domains: 2
- Electron Geometry: Linear
- Molecular Geometry: Linear
2. BCl₃ (Boron trichloride)
- Lewis Structure: B surrounded by 3 Cl atoms, single bonds
- Formal Charges: All atoms = 0
- Electron Domains: 3
- Electron Geometry: Trigonal planar
- Molecular Geometry: Trigonal planar
3. PO₂⁻ (Hypophosphite ion)
- Lewis Structure: P bonded to two O atoms, one single, one double; extra lone pair on P
- Formal Charges: One O = -1, others = 0
- Electron Domains: 3
- Electron Geometry: Trigonal planar
- Molecular Geometry: Bent
4. CH₂Cl₂ (Dichloromethane)
- Lewis Structure: C central, bonded to 2 H and 2 Cl
- Formal Charges: All atoms = 0
- Electron Domains: 4
- Electron Geometry: Tetrahedral
- Molecular Geometry: Tetrahedral
5. PBr₃ (Phosphorus tribromide)
- Lewis Structure: P central, 3 Br atoms, one lone pair on P
- Formal Charges: All atoms = 0
- Electron Domains: 4
- Electron Geometry: Tetrahedral
- Molecular Geometry: Trigonal pyramidal
6. PO₄³⁻ (Phosphate ion)
- Lewis Structure: P central, 4 O atoms, one with double bond, three with single and negative charge
- Formal Charges: Three O = -1, P = 0
- Electron Domains: 4
- Electron Geometry: Tetrahedral
- Molecular Geometry: Tetrahedral
7. SBr₄ (Sulfur tetrabromide)
- Lewis Structure: S central, 4 Br atoms, one lone pair
- Formal Charges: All atoms = 0
- Electron Domains: 5
- Electron Geometry: Trigonal bipyramidal
- Molecular Geometry: See-saw
8. IF₃ (Iodine trifluoride)
- Lewis Structure: I central, 3 F atoms, 2 lone pairs on I
- Formal Charges: All atoms = 0
- Electron Domains: 5
- Electron Geometry: Trigonal bipyramidal
- Molecular Geometry: T-shaped
9. BrF₅ (Bromine pentafluoride)
- Lewis Structure: Br central, 5 F atoms, 1 lone pair
- Formal Charges: All atoms = 0
- Electron Domains: 6
- Electron Geometry: Octahedral
- Molecular Geometry: Square pyramidal
10. XeF₄ (Xenon tetrafluoride)
- Lewis Structure: Xe central, 4 F atoms, 2 lone pairs
- Formal Charges: All atoms = 0
- Electron Domains: 6
- Electron Geometry: Octahedral
- Molecular Geometry: Square planar
11. NH₄⁺ (Ammonium ion)
- Lewis Structure: N central, 4 H atoms, positive charge on molecule
- Formal Charges: N = +1, each H = 0
- Electron Domains: 4
- Electron Geometry: Tetrahedral
- Molecular Geometry: Tetrahedral
Summary Explanation
Each molecule’s shape is determined by the number of regions of electron density (electron domains) around the central atom. These regions include bonding pairs and lone pairs. The electron domain geometry considers all electron regions, while the molecular geometry only considers atoms.
For example, CO₂ has two double bonds, resulting in two electron domains and a linear shape. In contrast, BCl₃ has three bonding regions forming a trigonal planar structure. Molecules like CH₂Cl₂ and NH₄⁺ have four electron domains, resulting in tetrahedral geometry. When lone pairs are present, as in PBr₃ and IF₃, the molecular geometry deviates from the electron geometry due to lone pair repulsion.
Formal charges are calculated by comparing the valence electrons of an atom with the electrons assigned to it in the Lewis structure. Most stable structures have formal charges close to zero. In ions like PO₄³⁻, resonance is important because the charge is delocalized.
Molecules like BrF₅ and XeF₄, with expanded octets, showcase the ability of elements in period 3 or beyond to hold more than eight electrons. These elements form geometries such as square pyramidal and square planar due to lone pairs occupying equatorial or axial positions.
Overall, understanding electron domains helps predict and explain molecular shapes and reactivities.
