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Chapter 12: Problem 148

Micelles are spherical, although they are usually drawn as a flat cross section (as shown on page 495). Why wouldn't micelles exist in water as flat, two-dimensional structures?

Short Answer

Expert verified
Micelles cannot exist in water as flat, two-dimensional structures because such an arrangement would not fully satisfy the hydrophilic and hydrophobic behaviors of amphipathic molecules. A spherical structure is necessary for all hydrophilic "heads" to be in contact with water and all hydrophobic "tails" to avoid water. In a three-dimensional spherical structure, the tails are grouped in the center, and the heads form the outer surface.

Step by step solution

01

Understand what micelles are

Micelles are self-assembling, organise structures that amphipathic molecules (like certain kinds of fats or detergents) form when exposed to aqueous solutions. They are made up of individual molecules arranged so that the hydrophilic (water-loving) "head" regions of the molecules are exposed to the water, and the hydrophobic (water-fearing) "tail" regions are hidden on the inside, away from the water.
02

Discuss about hydrophilic and hydrophobic behavior

Hydrophilic means attracting water, and in an aqueous environment, the hydrophilic heads of the amphipathic molecules will naturally want to be in contact with water. On the other hand, hydrophobic means repelling water, the hydrophobic tails will want to avoid contact with the water.
03

Understand the structure of a micelle

When in water, the amphipathic molecules arrange themselves into a shape where all the hydrophilic heads can be in contact with water and all the hydrophobic tails are grouped together, protected from the water. This is what forms the structure of a micelle.
04

Explain why micelles are not flat

Creating a flat, two-dimensional structure would not allow all the hydrophobic tails to completely avoid water - only those in the center of the structure would be protected. In order to allow every tail to avoid water and every head to be in contact with water, the molecules must arrange themselves in a three-dimensional, spherical structure where the hydrophobic tails are all inside, and the hydrophilic heads form the outer surface that's in contact with the water.
05

Summarize the answer

Therefore, micelles cannot exist in water as flat, two-dimensional structures because such an arrangement wouldn't fully satisfy the hydrophilic and hydrophobic behaviors of the amphipathic molecules. All the hydrophilic "heads" need to be in contact with water and all the hydrophobic "tails" need to avoid water, which is only possible in a three-dimensional spherical structure where the tails are grouped in the center and the heads form the outer surface.

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