July 7, 2021
Why do molecules absorb IR radiation? 🤔
- Think of bonds between atoms as vibrating springs.
- Each bond has it’s own frequency of vibration.
- Depends on types of atoms and types of bond.
- When exposed to IR radiation each bond absorbs energy at a particular frequency.
- This causes it vibrate more vigorously.
A typical IR spectrum:
- X-axis shows wavenumber in cm-1
- Y-axis shows percentage transmittance.
- Absorptions are described as strong, medium or hydrogen bonded.
- Below 1500 cm-1 is the fingerprint region.
- Typical absorption occur at about 3500 cm-1 for O-H bonds1750 cm-1 for C=O bonds
This table is very useful in AS/A-level Chemistry, as it shows the corresponding bond in different range of wavenumbers. 👩🏫
You will need this table to identify bonds and compounds!
The IR Spectroscopy below is a great example of how you can identify the bonds of a compound!
References:
- https://www.savemyexams.co.uk/notes/as-chemistry-cie/4-analysis-as/4-1-analytical-techniques-as/4-1-1-infra-red-spectroscopy-as/
- https://www.tes.com/teaching-resource/ir-spectroscopy-ocr-a-level-chemistry-11839252
This is the end of the topic!
Drafted by Cherry (Chemistry)