An AB5 molecule adopts the geometry shown here. (b) Do you think there are any nonbonding electron pairs on atom A?

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Identify the molecular geometry of the AB5 molecule shown in the image. The geometry appears to be trigonal bipyramidal.

Recall that in a trigonal bipyramidal geometry, the central atom (A) is surrounded by five atoms (B) with three atoms in the equatorial plane and two atoms in the axial positions.

Determine the electron domain geometry around the central atom (A). For a molecule with five bonding pairs and no lone pairs, the electron domain geometry is also trigonal bipyramidal.

Consider the presence of nonbonding electron pairs on the central atom (A). In a trigonal bipyramidal geometry, if there were any nonbonding electron pairs, they would occupy equatorial positions to minimize electron pair repulsion.

Conclude that since the molecule adopts a trigonal bipyramidal geometry with five bonding pairs and no lone pairs, there are no nonbonding electron pairs on atom A.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Molecular Geometry

Molecular geometry refers to the three-dimensional arrangement of atoms within a molecule. In the case of an AB5 molecule, where 'A' is the central atom and 'B' represents five surrounding atoms, the geometry is typically trigonal bipyramidal. Understanding this geometry is crucial for predicting the spatial orientation of the atoms and the potential presence of lone pairs.

VSEPR Theory

Valence Shell Electron Pair Repulsion (VSEPR) theory is a model used to predict the geometry of molecules based on the repulsion between electron pairs in the valence shell of the central atom. According to VSEPR, electron pairs, whether bonding or nonbonding, will arrange themselves to minimize repulsion, which helps determine the molecular shape and the presence of lone pairs.

Lone Pairs

Lone pairs are pairs of valence electrons that are not involved in bonding and are localized on a single atom. In the context of the AB5 molecule, the presence of lone pairs on atom A would influence its geometry and the angles between the surrounding B atoms. Identifying lone pairs is essential for accurately predicting molecular shape and reactivity.

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Textbook Question

Ethyl propanoate, CH₃CH₂COOCH₂CH₃, gives a fruity pineapple-like smell. (e) What are the approximate bond angles around each carbon atom in the molecule?

Textbook Question

An AB5 molecule adopts the geometry shown here. (c) Suppose the B atoms are halogen atoms. Of which group in the periodic table is atom A a member: (i) Group 15, (ii) Group 16, (iii) Group 17, (iv) Group 18, or (v) More information is needed?

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Textbook Question

The O¬H bond lengths in the water molecule 1H2O2 are 96 pm, and the H¬O¬H angle is 104.5°. The dipole moment of the water molecule is 1.85 D. (b) Calculate the magnitude of the bond dipole of the O¬H bonds. (Note: You will need to use vector addition to do this.)

Textbook Question

Ethyl propanoate, CH₃CH₂COOCH₂CH₃, gives a fruity pineapple-like smell. (a) Draw the Lewis structure for the molecule, assuming that carbon always forms four bonds in its stable compounds. (b) How many s and how many p bonds are in the molecule?