Draw the Lewis structure for ICl4- and answer the questions that follow. Do not include overall ion charges or formal charges in your drawing. b What is the electron-pair geometry for I in ICl4- ? c What is the the shape (molecular geometry) of ICl4-?
The Correct Answer and Explanation is:
Correct Answers:
a. Lewis Structure of ICl₄⁻
The central iodine (I) atom is surrounded by 4 chlorine (Cl) atoms and has 2 lone pairs of electrons. Each Cl is bonded to iodine with a single bond. The structure looks like this:
lessCopyEdit Cl
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Cl — I — Cl
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Cl
Also, include two lone pairs on iodine, placed opposite each other in the octahedral arrangement, making a total of six regions of electron density.
b. Electron-pair geometry for I in ICl₄⁻:
Octahedral
c. Molecular geometry (shape) of ICl₄⁻:
Square planar
Explanation
To draw the Lewis structure of ICl₄⁻, first count the total valence electrons. Iodine has 7 valence electrons, and each chlorine also has 7. Since there are four chlorine atoms, that gives 4 × 7 = 28 electrons. Add iodine’s 7 for a total of 35, and include 1 more for the negative charge, giving a total of 36 valence electrons.
Start by placing iodine in the center and forming single bonds to the four chlorine atoms. Each single bond uses 2 electrons, so 4 bonds use 8 electrons. That leaves 28 electrons. Place three lone pairs (6 electrons) on each chlorine to satisfy the octet rule. That uses 4 × 6 = 24 electrons, leaving 4 electrons. These remaining 4 electrons are placed as two lone pairs on the central iodine atom.
Now iodine has 4 bond pairs and 2 lone pairs, totaling 6 regions of electron density. According to VSEPR theory, 6 electron regions adopt an octahedral electron-pair geometry. However, since only 4 positions are occupied by atoms (the chlorines), and two are occupied by lone pairs, the actual shape is square planar. The lone pairs occupy positions opposite each other to minimize repulsion, and the four chlorine atoms form a flat square around the iodine atom.
This square planar geometry is common for species with six regions of electron density and two lone pairs, such as in d⁸ metal complexes or hypervalent main group compounds like ICl₄⁻.
