# What are the Differences between bending and stretching?

Apr 19, 2018

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 $C {O}_{2} \mathmr{and} {H}_{2} O$)

Jul 26, 2018

Here are the key differences.

$\underline{\text{Motion"" ""Rel. Frequency"" "" ""Desc."" "" "" "" "" }}$
$\text{Str."" "" "color(white)(/)"Higher"" "" "" "" "" ""Bond length varies}$
$\text{Bend"" "" ""Lower"" "" "" "" "" ""Bond angle varies}$

Visual examples are shown below for stretching and bending of $\text{H"_2"O}$. Together they are called the vibrational modes of water:

You can see that bends are often on the order of $t i l \mathrm{de} \nu = 400 - 1600 {\text{cm}}^{- 1}$, while stretches are often on the order of $t i l \mathrm{de} \nu = 1600 - 4000 {\text{cm}}^{- 1}$.

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