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Ch.11 - Liquids and Intermolecular Forces
Brown - Chemistry: The Central Science 14th Edition
Brown14th EditionChemistry: The Central ScienceISBN: 9780134414232Not the one you use?Change textbook
All textbooksBrown 14th EditionCh.11 - Liquids and Intermolecular ForcesProblem 21b,c
Chapter 11, Problem 21b,c

Which member in each pair has the greater dispersion forces? (b) CO2 or CO, (c) SiH4 or GeH4.

Verified step by step guidance
1
Understand that dispersion forces, also known as London dispersion forces, are a type of van der Waals force that occur between all atoms and molecules due to the temporary fluctuations in electron density.
Recognize that the strength of dispersion forces generally increases with the size of the electron cloud, which is related to the molar mass and the number of electrons in the molecule.
Compare the molar masses of SiH4 and GeH4. Silicon (Si) has a lower atomic mass than Germanium (Ge), so SiH4 will have a lower molar mass than GeH4.
Consider the number of electrons in each molecule. GeH4 has more electrons than SiH4 because Germanium has more electrons than Silicon.
Conclude that GeH4, having a larger molar mass and more electrons, will have greater dispersion forces compared to SiH4.

Key Concepts

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

Dispersion Forces

Dispersion forces, also known as London dispersion forces, are weak intermolecular forces arising from temporary fluctuations in electron density within molecules. These fluctuations create instantaneous dipoles that induce dipoles in neighboring molecules, leading to an attractive force. The strength of dispersion forces increases with the size and polarizability of the molecules involved.

Molecular Size and Polarizability

Polarizability refers to the ease with which the electron cloud of a molecule can be distorted by an external electric field or nearby charges. Larger molecules, like GeH4 compared to SiH4, generally have more electrons and a larger electron cloud, making them more polarizable. This increased polarizability results in stronger dispersion forces.
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Molecular Polarity

Comparative Analysis of Molecular Structures

When comparing molecular structures, it is essential to consider factors such as atomic size, molecular weight, and the number of electrons. In the case of SiH4 and GeH4, GeH4 has a larger atomic radius and more electrons due to the presence of germanium instead of silicon. This difference contributes to the greater dispersion forces in GeH4 compared to SiH4.
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Related Practice
Textbook Question

Ethylene glycol (HOCH2CH2OH), the major substance in antifreeze, has a normal boiling point of 198 °C. By comparison, ethyl alcohol (CH3CH2OH) boils at 78 °C at atmospheric pressure. Ethylene glycol dimethyl ether (CH3OCH2CH2OCH3) has a normal boiling point of 83 °C, and ethyl methyl ether (CH3CH2OCH3) has a nomral boiling point of 11 °C. (a) Explain why replacement of a hydrogen on the oxygen by a CH3 group generally results in a lower boiling point.

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Textbook Question

Which member in each pair has the stronger intermolecular dispersion forces? (a) Br2 or O2 (b) CH3CH2CH2CH2SH or CH3CH2CH2CH2CH2SH (c) CH3CH2CH2Cl or (CH3)2CHCl

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Textbook Question

True or false: (b) For the noble gases the dispersion forces decrease while the boiling points increase as you go down the column in the periodic table.

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Textbook Question

Which member in each pair has the greater dispersion forces? (a) H2O or H2S,

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Textbook Question

True or false: (e) The larger the atom, the more polarizable it is.

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