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What are the differences between stretching vibration and bending vibrations?

1 Answer
Dec 22, 2014

Stretching vibrations change bond lengths. Bending vibrations change bond angles.

Stretching Vibrations

A stretching vibration changes the bond length. There are two types of stretching vibrations.

In symmetric stretching, two or more bonds vibrate in and out together.

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In asymmetric stretching, some bonds are getting shorter at the same time as others are getting longer.

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Bending Vibrations

Bending vibrations change the angle between two bonds.

There are four types of bending vibration.

Scissoring is the movement of two atoms toward and away from each other.

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Rocking is like the motion of a pendulum on a clock, but an atom is the pendulum and there are two instead of one.

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Wagging is like the motion in which you make a "V" sign with your fingers and bend them back and forth from your wrist.

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Twisting is a motion as if the atoms were walking on a treadmill.

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Each type of vibration contributes to an infrared spectrum. For example, here is the spectrum of formaldehyde, H₂C=O.

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