Problem 47 - A Complete Resource Book in Chemistry for JEE Main

Question

The shape of IF \(_{7}\) molecule is (a) pentagonal bipyramidal (b) trigonal pyramidal (c) tetrahedral (d) square planar

Step-by-Step Solution

Answer

The shape of IF _{7} is pentagonal bipyramidal.

Step 1: Understanding the Question

We need to determine the molecular geometry of the iodine heptafluoride molecule, denoted as IF _{7}. The options suggest various geometrical shapes for this molecule. To solve this, we must use the VSEPR (Valence Shell Electron Pair Repulsion) theory.

Step 2: Determine the Central Atom and Valence Electrons

The central atom is Iodine (I) in IF _{7}. Iodine belongs to Group 17 of the Periodic Table and has 7 valence electrons. Each Fluorine (F) atom contributes 1 electron, for a total of 7 fluorine atoms contributing 7 electrons.

Step 3: Count Total Valence Electrons

Add the valence electrons from Iodine and the 7 Fluorine atoms: 7 (from Iodine) + 7 (from Fluorines) = 14 electrons.

Step 4: Determine Electron-Region Geometry

In VSEPR theory, the arrangement of electron pairs around the central atom dictates the geometry. For 7 bonding pairs (since all are bonds with fluorine and there are no lone pairs), the geometry is five equatorial atoms and two axial atoms, forming a pentagonal bipyramidal structure.

Step 5: Decide the Correct Molecular Shape

According to the VSEPR and the distribution of electron pairs, IF _{7} has a pentagonal bipyramidal shape. This matches option (a).

Key Concepts

Molecular Geometry

Molecular geometry is all about understanding how atoms are arranged in a molecule. This layout can tell us a lot about the properties and behavior of a molecule. To figure out a molecule's shape, we often turn to VSEPR theory. This theory helps us predict how electron pairs will orient themselves around a central atom to minimize repulsion. By understanding these arrangements, we can determine if a molecule is linear, angular, tetrehadral and so on. The geometry of a molecule influences physical and chemical characteristics, such as polarity and reactivity.

• Molecules aim to have angles between bonds that reduce repulsion.
• Electron pairs, both bonding and lone pairs, influence this arrangement.
• Shapes could be linear, trigonal planar, tetrahedral, among others.

Knowing molecular geometry is crucial in fields like chemistry and biology, as it affects interactions and functions.

Iodine Heptafluoride

Iodine heptafluoride, or IF _{7}, is an intriguing molecule because of its unique configuration. It is one of the rare examples of molecules where a central atom has more than four atoms bonded to it. In IF _{7}, iodine is the central atom, and it's surrounded by seven fluorine atoms.
This molecule exhibits a distinctive geometry that deviates from most molecules we encounter:

• The iodine atom uses its seven valence electrons to form bonds with each fluorine atom.
• This bonding situation arises due to iodine's ability to expand its valence shell beyond the typical octet.
• As a result, it adopts a particular shape to accommodate these bonds.

Studying iodine heptafluoride can enhance understanding of molecular geometries involving heavy transition elements.

Valence Electrons

Valence electrons are crucial in determining molecular structure, reactivity, and bonding possibilities. These electrons are found in an atom's outer shell and are most involved in chemical reactions. For atoms to achieve stability, they often seek to have full valence shells, similar to noble gases.

• For iodine, there are 7 valence electrons, given its position in Group 17.
• Fluorine, too, has 7 valence electrons, contributing one to each bond with iodine.
• In IF _{7}, iodine shares one valence electron with each of seven fluorine atoms, resulting in a total of 14 valence electrons involved in bonding.

Valence electrons play a fundamental role in forming the pentagonal bipyramidal shape by dictating the spatial arrangement of atoms and bonds in a molecule.

Pentagonal Bipyramidal Shape

The pentagonal bipyramidal shape is an arrangement found in some specific molecules like iodine heptafluoride. This geometric shape arises when a molecule has a central atom bonded to seven atoms with no lone pairs on the central atom. In this structure, five atoms form a pentagonal planar around the central atom, while two atoms are located axially above and below this plane.

• The geometry results from distributing seven bonding electron pairs around the central atom.
• This distribution minimizes repulsion between electron pairs according to VSEPR theory.
• It can be visualized as a molecular structure having two pyramids sharing a pentagonal base.

Recognizing this shape helps chemists predict and understand the properties of substances, providing insight into the behavior of complex molecules like IF _{7}.