Which member in each pair has the stronger intermolecular dispersion forces? (a) Br 2 or O 2 (b) CH 3 CH 2 CH 2 CH 2 SH or CH 3 CH 2 CH 2 CH 2 CH 2 SH (c) CH 3 CH 2 CH 2 Cl or (CH 3 ) 2 CHCl

Hello everyone. Today. We are being asked to compare the inter molecular dispersion force of. We have two compounds here. And so the first thing we're gonna do is we want to go through our answer choices. So right off the bat we can see That answer. Choice A is the correct one. And in a minute we'll go through why each of the other ones aren't the same, Aren't the correct answers. So when evaluating these compounds, we have to look at the molecular weight first to determine what inter molecular force they may have. And since we only have carbon, hydrogen and bro means we know we can only stick with di pole dipole interactions. And so they both have the same weight. So both of these have a weight of 175 g per mole. They will have the same number of carbons, hydrogen and bromine atoms. When you have smaller molecular weight, you generally have weaker inter molecular forces. And since they're the same, we have to move on to our second factor. So we set our first factor as we look at the molecular weight for a second we look at branch versus linear. And we'd say that branched compounds will have higher boiling points due to having less surface area. And so since we'll say that branched will have less of a boiling point due to less surface area to cover. And so since the second compound here is branched, it has a weaker inter molecular force and therefore the linear chain which is the first compound will therefore have a stronger inter molecular dispersion force. I hope this helped, and until next time.

Ch.11 - Liquids and Intermolecular Forces

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Brown 15th Edition

Ch.11 - Liquids and Intermolecular Forces

Problem 24

Chapter 11, Problem 24

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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Identify the type of intermolecular forces present in both molecules. Both CH3CH2CH2Cl and (CH3)2CHCl primarily exhibit dispersion forces (London dispersion forces), which are influenced by the molar mass and shape of the molecule.

Compare the molar masses of the two molecules. Generally, a higher molar mass leads to stronger dispersion forces because there are more electrons that can contribute to temporary dipoles.

Analyze the molecular shapes and sizes. Molecules with a larger surface area in contact can have stronger dispersion forces because there are more opportunities for temporary dipoles to interact.

Consider the branching in the molecules. More branching typically reduces the surface area in contact and can lead to weaker dispersion forces compared to a less branched isomer.

Based on the molar mass, molecular shape, and degree of branching, determine which molecule would have the stronger dispersion forces.

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Key Concepts

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

Intermolecular Forces

Intermolecular forces are the forces of attraction or repulsion between molecules. They play a crucial role in determining the physical properties of substances, such as boiling and melting points. The main types of intermolecular forces include hydrogen bonding, dipole-dipole interactions, and dispersion forces, with dispersion forces being the weakest and arising from temporary dipoles in molecules.

Dispersion Forces

Dispersion forces, also known as London dispersion forces, are a type of van der Waals force that occur due to the momentary distribution of electron density in atoms or nonpolar molecules. These forces increase with the size and polarizability of the molecules involved. Larger molecules with more electrons can create stronger temporary dipoles, leading to stronger dispersion forces.

Molecular Structure and Polarity

The molecular structure and polarity of a compound significantly influence its intermolecular forces. In the given compounds, the branching and presence of chlorine affect how closely molecules can pack together and the strength of their dispersion forces. Generally, less branched molecules can have stronger dispersion forces due to a larger surface area for interactions compared to more branched counterparts.