6. The correct shape of the [TeF5]– ion on the basis of VSEPR theory is
a. trigonal bipyramidal
b. square pyramidal
c. pentagonal planar
d. see-saw
The correct shape of the [TeF₅]⁻ ion according to VSEPR theory is square pyramidal.
VSEPR Analysis
Tellurium (Te) in [TeF₅]⁻ has 6 valence electrons, each fluorine contributes 1 for bonding, and the negative charge adds 1 more, yielding 42 valence electrons total. The Lewis structure shows Te bonded to 5 F atoms (5 bonding pairs) with 1 lone pair on Te, giving 6 electron domains for octahedral electron geometry. Lone pairs occupy axial positions in octahedral arrangements, distorting the molecular shape to square pyramidal with 5 equatorial F atoms.
Option Explanations
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Trigonal bipyramidal: Matches AX₅ (5 bonding pairs, 0 lone pairs), like PF₅, but [TeF₅]⁻ has 6 domains.
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Square pyramidal: Correct for AX₅E (5 bonding pairs, 1 lone pair), as in IF₅ or [XeF₅]⁺ analogs.
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Pentagonal planar: Fits AX₅ for 7 domains (like XeF₅⁺), not applicable here.
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See-saw: Applies to AX₄E (5 domains), like SF₄, ignoring the extra domain.
The shape of [TeF5]- ion according to VSEPR theory is square pyramidal, a key concept for CSIR NET Life Sciences and JEE Chemistry exams. VSEPR theory predicts molecular geometry by minimizing repulsion among 6 electron pairs around Te: 5 Te-F bonds and 1 lone pair form octahedral electron geometry, with the lone pair apical for square pyramidal molecular shape.
Why Square Pyramidal?
Te (group 16) expands octet via d orbitals (sp³d² hybridization). Steric number 6 (AX₅E notation) positions the lone pair opposite the pyramid base, compressing basal angles below 90°. This mirrors IF₅, confirming experimental validity.
Ruling Out Other Shapes
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Trigonal bipyramidal suits 5-domain AX₅, lacking the lone pair’s influence.
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Pentagonal planar requires 7 domains (AX₇ or AX₅E₂).
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See-saw fits 5-domain AX₄E, undercounting pairs.
Mastering [TeF5]- ion VSEPR theory shape boosts exam scores—practice with similar polyhalides like BrF₅.
