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Ch.9 - Molecular Geometry and Bonding Theories
All textbooksBrown 14th EditionCh.9 - Molecular Geometry and Bonding TheoriesProblem 54a
Chapter 9, Problem 54a

(a) Which geometry and central atom hybridization would you expect in the series BH4-, CH4, NH4+?

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1
Identify the central atom in each of the given species: BH4-, CH4, and NH4+. The central atoms are B, C, and N respectively.
Determine the number of valence electrons for each central atom: Boron (B) has 3, Carbon (C) has 4, and Nitrogen (N) has 5 valence electrons.
Consider the charge on each species and adjust the total number of electrons accordingly: BH4- has an extra electron, CH4 is neutral, and NH4+ has one less electron.
Use the VSEPR (Valence Shell Electron Pair Repulsion) theory to predict the geometry: All three species have four regions of electron density around the central atom, leading to a tetrahedral geometry.
Determine the hybridization of the central atom: For a tetrahedral geometry, the hybridization is sp^3. Therefore, the central atom in each species (B, C, and N) is sp^3 hybridized.

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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. According to this theory, electron pairs, whether bonding or lone pairs, will arrange themselves to minimize repulsion, leading to specific molecular shapes such as tetrahedral, trigonal planar, or linear.
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Hybridization

Hybridization is the concept of mixing atomic orbitals to form new hybrid orbitals that can accommodate bonding. For example, in methane (CH4), the carbon atom undergoes sp3 hybridization, resulting in four equivalent sp3 hybrid orbitals that arrange themselves in a tetrahedral geometry, allowing for maximum separation and minimal repulsion between the bonds.
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Molecular Ions

Molecular ions are charged species formed when molecules gain or lose electrons. In the case of BH4-, CH4, and NH4+, the presence of a charge affects the hybridization and geometry. For instance, NH4+ has a positive charge, which influences its electron count and results in a tetrahedral shape similar to CH4, while BH4- has a negative charge, also leading to a tetrahedral arrangement.
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Related Practice
Textbook Question

What is the hybridization of the central atom in (d) NO2?

Textbook Question

Shown here are three pairs of hybrid orbitals, with each set at a characteristic angle. For each pair, determine the type of hybridization, if any, that could lead to hybrid orbitals at the specified angle. (a)


(b)


(c)

Textbook Question
(c) Write the formulas for the analogousspecies of the elements of period 3;
Textbook Question

(b) What would you expect for the magnitude and direction of the bond dipoles in this series?

Textbook Question

(a) Draw a picture showing how two p orbitals on two different atoms can be combined to make a σ bond. (b) Sketch a π bond that is constructed from p orbitals.

Textbook Question

(c) Which is generally stronger, a s bond or a p bond? Explain.