What is the Electron-Pair Geometry for I in IBr₃?
The electron-pair geometry for iodine (I) in IBr₃ is trigonal bipyramidal. Understanding this requires looking at iodine's valence electrons and how they participate in bonding with the bromine atoms.
Let's break down why:
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Iodine's Valence Electrons: Iodine, being in Group 17 of the periodic table, possesses seven valence electrons.
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Bonding with Bromine: In IBr₃, iodine forms three single bonds with three bromine atoms, using three of its valence electrons.
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Lone Pairs: This leaves iodine with four remaining valence electrons, which arrange themselves as two lone pairs.
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VSEPR Theory: The Valence Shell Electron Pair Repulsion (VSEPR) theory dictates that electron pairs (both bonding and lone pairs) around a central atom will arrange themselves to minimize repulsion. To achieve this minimum repulsion with three bonding pairs and two lone pairs around the central iodine atom, the optimal arrangement is a trigonal bipyramidal geometry.
Therefore, the electron-pair geometry is trigonal bipyramidal, even though the molecular geometry (considering only the positions of the atoms, not the lone pairs) is T-shaped. This distinction is crucial. Electron-pair geometry refers to the overall arrangement of electron pairs, while molecular geometry focuses only on the arrangement of atoms.
What is the difference between electron-pair geometry and molecular geometry?
This is a common point of confusion. Here's a clearer explanation:
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Electron-pair geometry: This describes the arrangement of all electron pairs around the central atom, including both bonding pairs and lone pairs. It dictates the overall spatial distribution of electrons.
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Molecular geometry: This describes the arrangement of only the atoms around the central atom. It ignores the lone pairs, focusing solely on the shape created by the atoms themselves.
In the case of IBr₃, the five electron pairs (three bonding, two lone) lead to a trigonal bipyramidal electron-pair geometry. However, the two lone pairs occupy equatorial positions to minimize repulsion, resulting in a T-shaped molecular geometry.
What is the hybridization of iodine in IBr₃?
The hybridization of iodine in IBr₃ is sp³d. This hybridization allows for the formation of five hybrid orbitals, which accommodate the three bonding pairs and two lone pairs in the trigonal bipyramidal electron-pair geometry.
Why is the molecular geometry of IBr₃ T-shaped?
The two lone pairs on the iodine atom occupy the equatorial positions in the trigonal bipyramidal arrangement. This is because the equatorial positions experience less repulsion than the axial positions. Consequently, the three bromine atoms are arranged at 90° angles to each other resulting in the T-shaped molecular geometry.
This comprehensive explanation covers the key aspects of IBr₃'s geometry, addressing the core question and related concepts. Understanding the difference between electron-pair and molecular geometry is essential for accurately predicting the shapes of molecules.
