Question

What are the Differences between bending and stretching?

Answer 1

see below

Explanation:

stretching is the variation of the bond distance caused by a vibration. It can occur if a molecula has at least 2 atoms. Bending is the variation of the angle of the bond caused by a vibration. For having bending you must have a molecula with at least 3 atoms (for example `CO_2 or H_2O`)

Answer 2

Here are the key differences.

`ul("Motion"" ""Rel. Frequency"" "" ""Desc."" "" "" "" "" ")`
`"Str."" "" "color(white)(/)"Higher"" "" "" "" "" ""Bond length varies"`
`"Bend"" "" ""Lower"" "" "" "" "" ""Bond angle varies"`

Visual examples are shown below for stretching and bending of `"H"_2"O"`. Together they are called the vibrational modes of water:

![)

You can see that bends are often on the order of `tildenu = 400 - 1600 "cm"^(-1)`, while stretches are often on the order of `tildenu = 1600 - 4000 "cm"^(-1)`.

Bends are therefore found in the so-called fingerprint region of the IR spectrum (the right-hand side, lower frequency).