Draw the Lewis structure for each of the following molecules or ions, and predict their electron-domain and molecular geometries: HCN, SO2, SF4, PF6-, NH4+, N2, AsF5, CH4, BrF3, ClO2, XeF2, BrO2
The Correct Answer and Explanation is:
1. HCN (Hydrogen Cyanide)
Lewis Structure:
- H is bonded to C, and C is triple-bonded to N (C≡N).
- There are 10 valence electrons in total, which are distributed as follows: H (2), C (4), N (5).
- The C≡N bond is a triple bond, with one lone pair on C and one lone pair on N.
Electron-Domain Geometry: Linear
Molecular Geometry: Linear
The molecule has a straight line structure, with no lone pairs on the central atoms.
2. SO2 (Sulfur Dioxide)
Lewis Structure:
- S is double-bonded to both O atoms (O=S=O).
- The sulfur has one lone pair, and each oxygen has two lone pairs.
Electron-Domain Geometry: Trigonal Planar
Molecular Geometry: Bent
The lone pair on sulfur causes a bent shape due to electron repulsion.
3. SF4 (Sulfur Tetrafluoride)
Lewis Structure:
- S is in the center, bonded to four F atoms (S-F).
- There are two lone pairs on sulfur.
Electron-Domain Geometry: Trigonal Bipyramidal
Molecular Geometry: See-saw
The lone pairs occupy equatorial positions, causing the see-saw shape.
4. PF6- (Hexafluorophosphate ion)
Lewis Structure:
- P is in the center, bonded to six F atoms (P-F).
- There are no lone pairs on the phosphorus atom, and the ion has an extra electron, giving it a negative charge.
Electron-Domain Geometry: Octahedral
Molecular Geometry: Octahedral
There is symmetry with no lone pairs, so the geometry is octahedral.
5. NH4+ (Ammonium Ion)
Lewis Structure:
- N is bonded to four H atoms (N-H).
- There are no lone pairs on nitrogen.
- The positive charge is on the nitrogen atom, indicating it has lost one electron.
Electron-Domain Geometry: Tetrahedral
Molecular Geometry: Tetrahedral
The geometry remains tetrahedral, as all four bonds are equivalent.
6. N2 (Nitrogen Molecule)
Lewis Structure:
- N≡N with each nitrogen having one lone pair.
- There are 10 valence electrons, distributed as follows: N (5) + N (5).
Electron-Domain Geometry: Linear
Molecular Geometry: Linear
The molecule is linear with a triple bond between the nitrogen atoms.
7. AsF5 (Arsenic Pentafluoride)
Lewis Structure:
- As is in the center, bonded to five F atoms (As-F).
- There are no lone pairs on arsenic.
Electron-Domain Geometry: Trigonal Bipyramidal
Molecular Geometry: Trigonal Bipyramidal
The arrangement is symmetric with no lone pairs.
8. CH4 (Methane)
Lewis Structure:
- C is in the center, bonded to four H atoms (C-H).
- There are no lone pairs on carbon.
Electron-Domain Geometry: Tetrahedral
Molecular Geometry: Tetrahedral
The geometry is tetrahedral, with all bonds equal and no lone pairs.
9. BrF3 (Bromine Trifluoride)
Lewis Structure:
- Br is bonded to three F atoms (Br-F).
- There are two lone pairs on bromine.
Electron-Domain Geometry: Trigonal Bipyramidal
Molecular Geometry: T-shaped
The lone pairs occupy equatorial positions, leading to the T-shaped geometry.
10. ClO2 (Chlorine Dioxide)
Lewis Structure:
- Cl is bonded to two O atoms (Cl=O).
- There is one lone pair on chlorine, and each oxygen has two lone pairs.
Electron-Domain Geometry: Bent
Molecular Geometry: Bent
The lone pair on chlorine causes the molecule to be bent, even though it would have been linear without the lone pair.
11. XeF2 (Xenon Difluoride)
Lewis Structure:
- Xe is bonded to two F atoms (Xe-F).
- There are three lone pairs on xenon.
Electron-Domain Geometry: Octahedral
Molecular Geometry: Linear
The three lone pairs occupy the equatorial positions, and the two F atoms are placed in a linear arrangement.
12. BrO2 (Bromine Dioxide)
Lewis Structure:
- Br is bonded to two O atoms (Br=O).
- There are two lone pairs on bromine.
Electron-Domain Geometry: Trigonal Planar
Molecular Geometry: Bent
The two lone pairs on bromine push the O atoms into a bent shape.
In summary, the molecular geometries vary due to the number of bonding and nonbonding electron pairs around the central atoms.
