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Ch.22 - The Main Group Elements
All textbooksMcMurry 8th EditionCh.22 - The Main Group ElementsProblem 63
Chapter 22, Problem 63

Describe the molecular geometry of: (a) GeH4 (b) NH3 (c) H2S

Verified step by step guidance
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Step 1: Determine the central atom and count the total number of valence electrons for each molecule. For GeH4, Ge is the central atom with 4 valence electrons, and each H contributes 1 electron, totaling 8 valence electrons. For NH3, N is the central atom with 5 valence electrons, and each H contributes 1 electron, totaling 8 valence electrons. For H2S, S is the central atom with 6 valence electrons, and each H contributes 1 electron, totaling 8 valence electrons.
Step 2: Draw the Lewis structure for each molecule. For GeH4, place Ge in the center and arrange the 4 H atoms around it, forming single bonds. For NH3, place N in the center with 3 H atoms bonded to it and a lone pair on N. For H2S, place S in the center with 2 H atoms bonded to it and 2 lone pairs on S.
Step 3: Apply the VSEPR (Valence Shell Electron Pair Repulsion) theory to predict the molecular geometry. For GeH4, with 4 bonding pairs and no lone pairs, the geometry is tetrahedral. For NH3, with 3 bonding pairs and 1 lone pair, the geometry is trigonal pyramidal. For H2S, with 2 bonding pairs and 2 lone pairs, the geometry is bent.
Step 4: Describe the bond angles based on the molecular geometry. In a tetrahedral geometry like GeH4, the bond angles are approximately 109.5°. In a trigonal pyramidal geometry like NH3, the bond angles are slightly less than 109.5° due to the lone pair repulsion. In a bent geometry like H2S, the bond angles are even smaller, typically around 104.5°.
Step 5: Summarize the molecular geometries: (a) GeH4 is tetrahedral, (b) NH3 is trigonal pyramidal, and (c) H2S is bent. These geometries are determined by the number of bonding pairs and lone pairs around the central atom, as predicted by VSEPR theory.

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 a model used to predict the geometry of individual molecules based on the repulsion between electron pairs in the valence shell of the central atom. According to this theory, electron pairs will arrange themselves as far apart as possible to minimize repulsion, leading to specific molecular shapes.
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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 GeH4, the germanium atom undergoes sp3 hybridization, resulting in four equivalent hybrid orbitals that arrange in a tetrahedral geometry. Understanding hybridization helps explain the bonding and shape of molecules.
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Molecular Geometry

Molecular geometry refers to the three-dimensional arrangement of atoms within a molecule. It is determined by the number of bonding pairs and lone pairs of electrons around the central atom. For instance, NH3 has a trigonal pyramidal shape due to one lone pair, while H2S has a bent shape because of two lone pairs, illustrating how lone pairs influence molecular structure.
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Related Practice
Textbook Question

Describe the molecular geometry of:

(a) H2Se

Textbook Question

Describe the molecular geometry of:

(b) AsH3

Textbook Question

Describe the molecular geometry of:

(c) SiH4

Textbook Question

What is a nonstoichiometric compound? Give an example, and account for its lack of stoichiometry in terms of structure.

Textbook Question

Explain why the hydrogen atoms in interstitial hydrides are mobile.