17.2 Infrared Spectroscopy
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What do all bonds do at any given time?
Vibrate
What does infrared radiation do to covalent bonds?
Is absorbed by them, making them bend or stretch more.
What is stretching in covalent bonds?
Rhythmic movement along the line between the atoms, so the distance between the 2 atomic centres increase and decreases
What is bending in covalent bonds?
Increasing and decreasing the bond angle
What does the amount that a bond stretches or bends depend on?
• Mass of atoms in the bond • Strength of the bond
What type of radiation can any bond absorb?
Radiation that has the same frequency as the natural frequency of the bond
How do greenhouse gases lead to global warming?
Greenhouse gases absorb and re-emit longer wavelength infrared radiation that increases the temperature of the atmosphere
Describe the steps of infrared spectroscopy.
1- Sample under investigation is placed inside an IR spectrometer 2- A beam of IR radiation in the range 200-4000cm^-1 is passed through the sample 3- The molecule absorbs some of the IR frequencies, and the emerging beam of radiation is analysed to identify the frequencies that have been absorbed by the sample 4- IR spectrometer is connected to a computer that plots a graph of transmittance against wavenumber.
What is infrared spectroscopy used for?
Identifying the functional groups present in organic molecules
What is used to measure the natural frequency of a bond?
Wavenumber, measured in cm^-1
What is % transmittance?
How much light is received at the detector
What are dips in the IR spectrum called?
Peaks
What is the fingerprint region?
An area of infrared spectrum below 1500cm^-1 that gives a characteristic pattern for different compounds.
What are the applications of IR spectroscopy?
• Identifying pollutants • Breathalysers