what are stretching vibrations ? Explain with figure the vibration of CH2 molecule.
Answers
Answer:
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. In asymmetric stretching, some bonds are getting shorter at the same time as others are getting longer.
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Explanation:
Answer:
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. . In asymmetric stretching, some bonds are getting shorter at the same time as others are getting longer.
If the molecule has more than two atoms, then things get more complicated. Suppose just one more atom is added so now there are three atoms like in water H2O where the two hydrogen atoms are both attached to the central oxygen atom. Remember with hydrogen there was one kind of stretching, but in water there are two kinds of stretching and four other kinds of vibration called bending vibrations as shown below.
The atoms in a CH2 group or molecules like water can vibrate in six different ways: symmetric and antisymmetric stretching, scissoring, rocking, wagging and twisting:
symmetric stretching: when the two attached atoms move away and toward the central atom at the same time.
antisymmetric stretching: When the two attached atoms do not move away and toward the central atom at the same time.
scissoring: Just like the name says scissoring is when the two atoms move away and toward each other
rocking: This motion is like a pendulum on a clock going back and forth only here an atom is the pendulum and there are two instead of one.
wagging: If a person holds up their hand in front of them and puts there two fingers in a "V" sign and bend there wrist toward and away from them. Here the tips of the fingers are the attached atoms and the wrist is the central atom.
twisting: This motion is like a person is walking on a treadmill where their waist is the central atom and their feet are the two attached atom
Molecules with more than three atoms
Molecules with more than three atoms are even more complicated and have even more vibrations which are sometimes called "vibrational modes". Each new vibrational mode is basically a different combination of the six shown above. The more atoms in the molecule the more ways they can be combined. For most molecules with N atoms the number of possible vibrations for that molecule is 3N - 6 while linear molecules, or molecules with there atoms in a straight line, have 3N-5 vibrational modes.