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Difficulty: HardMolecular Shapes, VSEPR Theory, and Hybridization

Sulfur tetrafluoride (SF4SF_4) and xenon tetrafluoride (XeF4XeF_4) are both covalent fluorides containing four fluorine atoms bonded to a central atom. Based on VSEPR theory and hybridization models, which of the following correctly pairs the molecular geometry and central atom hybridization state for SF4SF_4 and XeF4XeF_4, respectively?

  1. SF4SF_4: Seesaw geometry with sp3dsp^3d hybridization; XeF4XeF_4: Square planar geometry with sp3d2sp^3d^2 hybridizationAnswer
  2. B
    SF4SF_4: Trigonal bipyramidal geometry with sp3dsp^3d hybridization; XeF4XeF_4: Octahedral geometry with sp3d2sp^3d^2 hybridization
  3. C
    SF4SF_4: Tetrahedral geometry with sp3sp^3 hybridization; XeF4XeF_4: Tetrahedral geometry with sp3sp^3 hybridization
  4. D
    SF4SF_4: Square planar geometry with sp3d2sp^3d^2 hybridization; XeF4XeF_4: Seesaw geometry with sp3dsp^3d hybridization

Answer

SF4SF_4 has a seesaw molecular geometry with sp3dsp^3d hybridization on the sulfur atom, while XeF4XeF_4 has a square planar molecular geometry with sp3d2sp^3d^2 hybridization on the xenon atom.
For SF4SF_4, sulfur has 6 valence electrons forming 4 single bonds and retaining 1 lone pair, giving 5 electron domains (sp3dsp^3d hybridization). The lone pair occupies an equatorial site of the trigonal bipyramid, yielding a seesaw shape. For XeF4XeF_4, xenon has 8 valence electrons forming 4 single bonds and retaining 2 lone pairs, giving 6 electron domains (sp3d2sp^3d^2 hybridization). The two lone pairs lie opposite each other along the axial axis, resulting in a square planar geometry.

Step-by-Step Solution

1
Determine valence electron count and electron domains for SF4SF_4
Sulfur has 6 valence electrons. Bonding 4 fluorine atoms consumes 4 electrons, leaving 2 non-bonding electrons (1 lone pair). Total steric number = 4 bonding pairs + 1 lone pair = 5 electron domains.
VSEPR theory requires calculating the total number of electron pairs around the central atom.
2
Assign hybridization and molecular geometry for SF4SF_4
A steric number of 5 corresponds to sp3dsp^3d hybridization and trigonal bipyramidal electron geometry. With 1 equatorial lone pair, the molecular shape is seesaw.
Lone pairs prefer equatorial positions in trigonal bipyramidal systems to minimize electron repulsion, leading to a seesaw geometry.
3
Determine valence electron count and electron domains for XeF4XeF_4
Xenon has 8 valence electrons. Bonding 4 fluorine atoms consumes 4 electrons, leaving 4 non-bonding electrons (2 lone pairs). Total steric number = 4 bonding pairs + 2 lone pairs = 6 electron domains.
Steric number governs hybridization and electron arrangement for the central xenon atom.
4
Assign hybridization and molecular geometry for XeF4XeF_4
A steric number of 6 corresponds to sp3d2sp^3d^2 hybridization and octahedral electron geometry. With 2 axial lone pairs opposing each other (180° apart), the molecular geometry is square planar.
Axial placement of two lone pairs in an octahedral arrangement maximizes separation and produces a planar square arrangement of bonded fluorine atoms.

Key Concept

Molecular Shapes, VSEPR Theory, and Hybridization
Estimated Time:2m 0s
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Topics

Molecular Shapes, VSEPR Theory, and Hybridization

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