Problem 10 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

Shapes of certain interhalogen compounds are stated below. Which one of them is not correctly stated? [Main Online April 11, 2014] (a) \(\mathrm{IF}_{7}:\) pentagonal bipyramid (b) \(\mathrm{BrF}_{5}\) : trigonal bipyramid (c) \(\mathrm{BrF}_{3}\) : planar T-shaped (d) ICI. ' planar dimeric

Step-by-Step Solution

Answer

(b) \(\mathrm{BrF}_{5}\) : trigonal bipyramid is incorrectly stated.

Step 1: Identify Electron Geometry

The electron geometry describes the spatial arrangement of all the bonding and lone pairs of electrons around the central atom. For example, in \(\mathrm{IF}_{7}\), the geometry including 7 bonded pairs is a pentagonal bipyramid. Now identify the electron geometry for each given compound, keeping in mind that lone pairs will affect the molecular geometry.

Step 2: Determine Molecular Geometry

Molecular geometry is based on the arrangement of only the bonded atoms to the central atom after accounting for the lone pairs.- For \(\mathrm{BrF}_{5}\), if the electron geometry is octahedral (six regions of electron density), one of those would be a lone pair, making the molecular geometry square pyramidal.- For \(\mathrm{BrF}_{3}\), three regions of electron density are bonded and two are lone pairs, leading to a T-shaped geometry.

Step 3: Compare Each Option's Molecular Geometry

Now compare the determined molecular geometries with those stated in the exercise:- \(\mathrm{IF}_{7}\): Pentagonal bipyramid is correct.- \(\mathrm{BrF}_{5}\): Stated as trigonal bipyramid, but actual is square pyramidal.- \(\mathrm{BrF}_{3}\): Planar T-shaped, which is correct.- \(\mathrm{ICl}\): Assume it is iodide monol-chloride dimer; given as planar dimeric.

Step 4: Identify Incorrect Statement

From the comparison in Step 3, identify the incorrect statement. Clearly, the molecular geometry stated for \(\mathrm{BrF}_{5}\) is incorrect since it is actually square pyramidal and not trigonal bipyramidal.

Key Concepts

Interhalogen Compounds

Interhalogen compounds are fascinating molecules formed between two different halogens. Halogens, found in group 17 of the periodic table, include elements like fluorine \(F\), chlorine \(Cl\), bromine \(Br\), iodine \(I\), and astatine \(At\). These elements can bond together, creating compounds such as \(\text{IF}_7\), \(\text{BrF}_5\), and \(\text{ICl}\).
Interhalogen compounds are significant because they offer insights into the bonding and geometry of molecules with different halogens. Some key points about interhalogen compounds are:

• They often feature one halogen in excess, standing as the central atom.
• The central atom typically comes from a larger halogen due to its ability to accommodate more atoms around it.
• Interhalogen compounds can exhibit various geometries, depending on the number of atoms and electron pairs surrounding the central atom.

The study of these compounds helps us understand molecular geometry's impact on reactions and properties in chemistry.

Electron Geometry

Electron geometry considers the arrangement of all electron pairs (bonding and lone pairs) around a central atom. This includes both pairs utilized in bonds and those that are not engaged in bonding, known as lone pairs. Let's break down how electron geometry works:
- **Determining Electron Geometry:** The electron geometry depends on the steric number, which is the sum of bonded atoms and lone pairs around the central atom.- For example, in \(\text{BrF}_5\), the electron geometry is octahedral, with six positions filled by five bonding pairs and one lone pair.
By understanding electron geometry, we can predict:

• The spatial arrangement that minimizes repulsion between electron clouds.
• How variations in geometry influence molecular shape and physical properties.

This fundamental comprehension is crucial as the electron geometry serves as the foundation for determining the actual shape of the molecule, known as molecular geometry.

Shape of Molecules

The shape of a molecule, known as its molecular geometry, is influenced by the arrangement of bonded atoms around the central atom while considering the repulsion introduced by lone pairs. The presence of lone pairs can lead to an offset in the suggested geometry from the electron geometry. Let's consider some examples:
- **Molecular Geometry vs. Electron Geometry:** In \(\text{BrF}_5\), the electron geometry is octahedral; however, with one lone pair, the molecular geometry becomes square pyramidal.- **Influence of Lone Pairs:** Lone pairs on the central atom push bonding pairs closer together, thereby altering the molecule's shape.
Molecular geometry can vary greatly:

• Linear
• Tetrahedral
• Trigonal Planar
• Bent

Studying molecular shapes is essential in chemistry for comprehending how molecules interact, as well as predicting their reactivity, polarity, and physical properties. Knowing the shape helps chemists to better predict and understand reactions and interactions at a molecular level.