Question

The shape of \(\mathrm{IF}_{7}\) molecule is: (a) Pentagonal bipyramidal (b) Trigonal pyramidal (c) Tetrahedral (d) Square planar

Short answer

The shape of \( \mathrm{IF}_{7} \) molecule is pentagonal bipyramidal.

Step-by-step solution

Determine the Valence Electrons

Iodine (I) is in group 17 and thus has 7 valence electrons. Fluorine (F) is also in group 17, but since there are 7 F atoms bonding to I, we only focus on the electrons of I initially.

Count Total Electrons Involved

Since there are 7 fluorine atoms, each forming a single bond with iodine using one electron, consider these bonds to use 7 electrons from iodine's 7 valence electrons.

Apply VSEPR Theory

The bonding of 7 electron pairs around a central atom I means 7 bond pairs (no lone pairs left), resulting in a molecular shape of pentagonal bipyramidal based on VSEPR theory.

Identify Molecular Shape

Due to the arrangement of 7 bond pairs around the central iodine atom, the most stable arrangement is pentagonal bipyramidal. This involves 5 fluorine atoms in a planar pentagon and one fluorine atom above and one below the plane.

Key concepts

Molecular Geometry

Molecular geometry refers to the 3D arrangement of atoms within a molecule. It significantly influences the properties and reactions of a molecule. By analyzing molecular geometry, chemists can predict the behavior of the molecule in chemical reactions or its physical properties like polarity and phase of matter.

Geometry is determined by several factors, primarily the number of bonding pairs and lone pairs of electrons around a central atom. A common tool to predict molecular geometry is the Valence Shell Electron Pair Repulsion (VSEPR) theory. According to this theory, electron pairs arrange themselves to minimize repulsion, leading to a shape that keeps them as far apart as possible.

The shape of small molecules can often be described by standard geometries. These can include linear, trigonal planar, tetrahedral, and trigonal bipyramidal among others. More complex shapes, like pentagonal bipyramidal, arise when there are seven pairs of electrons around a central atom, leading to unique bond angles and shapes. Understanding these concepts equips students to better grasp how molecules interact and bond.

Valence Electrons

Valence electrons are the electrons in the outermost shell of an atom. They play a key role in chemical bonding, as they are the electrons most likely to participate in outer-shell activities and interactions. These electrons determine an element's chemical properties and its ability to form bonds with other elements.

The number of valence electrons can be determined by looking at an element's position in the periodic table. For instance, elements in group 17, such as iodine and fluorine, each have 7 valence electrons. In the bonding process, atoms will often share or transfer valence electrons to achieve full outer shells, which is often eight electrons (an octet).

Understanding valence electrons is crucial in predicting how atoms will bond in larger molecules. This is particularly useful in applying the VSEPR theory, which helps elucidate the shapes of molecules based on the distribution of these outer electrons.

Pentagonal Bipyramidal

The term "pentagonal bipyramidal" refers to a specific molecular geometry. This structure arises when seven pairs of bonding electrons surround a central atom. It is characterized by five atoms placed in a plane forming a pentagon, with two additional atoms positioned above and below this plane.

To visualize this shape, imagine a pentagon, the five corners of which are occupied by atoms, resembling a flat arrangement. Then, two other atoms sit above and below this planar setup, much like the points of a diamond resting within.

A prime example, and quite the intriguing one, of a molecule with pentagonal bipyramidal geometry is \(\mathrm{IF}_{7}\). In \(\mathrm{IF}_{7}\), iodine serves as the central atom, and the seven fluorine atoms form the unique shape. Such molecular geometry is essential in understanding how complex molecules fit in real-world systems and can aid in predicting the behavior of large polyatomic structures.