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Ch.9 - Molecular Geometry and Bonding Theories
Brown - Chemistry: The Central Science 14th Edition
Brown14th EditionChemistry: The Central ScienceISBN: 9780134414232Not the one you use?Change textbook
All textbooksBrown 14th EditionCh.9 - Molecular Geometry and Bonding TheoriesProblem 13a
Chapter 9, Problem 13a

(a) An AB2 molecule is linear. How many nonbonding electron pairs are around the A atom from this information?

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1
Identify the molecular geometry of the AB2 molecule. Given that the molecule is linear, this implies that the arrangement of atoms and electron pairs around the central atom A is in a straight line.
Recall VSEPR theory, which states that the shape of a molecule is determined by the repulsions between all electron pairs surrounding the central atom, including bonding and nonbonding pairs.
Determine the hybridization of the central atom A. For a linear shape in an AB2 molecule, the central atom typically has sp hybridization.
Understand that in sp hybridization, the central atom A has one s orbital and one p orbital mixing to form two sp hybrid orbitals, which are used to form sigma bonds with the two B atoms.
Conclude that since all available orbitals in sp hybridization are used for bonding and the molecule is linear, there are no nonbonding electron pairs (lone pairs) on the central atom A.

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Key Concepts

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

VSEPR Theory

Valence Shell Electron Pair Repulsion (VSEPR) Theory is used to predict the geometry of molecules based on the repulsion between electron pairs around a central atom. In the case of an AB2 molecule, the arrangement of bonding and nonbonding electron pairs determines the molecular shape, which in this instance is linear.
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Molecular Geometry

Molecular geometry refers to the three-dimensional arrangement of atoms in a molecule. For an AB2 molecule that is linear, the two B atoms are positioned 180 degrees apart, indicating that the central atom A has no lone pairs of electrons affecting the geometry, which is crucial for determining the number of nonbonding electron pairs.
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Molecular Geometry with Two Electron Groups

Lone Pairs

Lone pairs are pairs of valence electrons that are not involved in bonding and are localized on a single atom. In a linear AB2 molecule, the absence of lone pairs on the central atom A allows for the linear shape, indicating that there are zero nonbonding electron pairs around A.
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Related Practice
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For each of these contour representations of molecular orbitals, identify (c) whether the MO is bonding or antibonding (i)

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