17.2 Infrared Spectroscopy

Question 1

What property of molecules does infrared spectroscopy use to identify specific types of covalent bonds?

Answer 1

covalent bonds absorb infrared radiation.

(different types of covalent bonds absorb specific wavelengths of IR radiation

infrared spectroscopy detects absence of wavelengths (ie the ones absorbed by the covalent bonds)

therefore identifying the type of covalent bonds present in the molecule.)

Question 2

What happens when a covalent bond absorbs IR radiation?

Answer 2

vibrates (stretches/bends)

Question 3

What are the 2 types of vibration that may occur when a covalent bond absorbs IR radiation?

Answer 3

BEND

STRETCH

Question 4

What are the 2 factors affecting the extent that a covalent bond bends/stetches after absorbing IR radiation?

Answer 4

• MASS OF ATOMS
  
  • heavier atoms vibrate slower
• STRENGTH OF COVALENT BOND
  
  • stronger bonds vibrate faster

Question 5

How does the presence of greenhouse gases in the atmosphere affect the average global temperature?

Answer 5

• Radiation in form of visible light passes through atmosphere
  
  • absorbed by earth surface
• Some absorbed radiation re-emitted as longer wavelength IR radiation
  
  • absorbed by greenhouse gases, instead of leaving the atmosphere
• greenhouse gas molecules re-emit this energy
  
  • increases temperature

Question 6

Outline the process by which infrared spectroscopy can be used to identify functional groups:

Answer 6

1. sample placed in infrared spectrometer
2. beam of IR radiation in range 200-4000cm^-1 passed through sample
3. Molecule absorbs specific frequencies of IR radiation.
4. Computer plots graph of %transmission against wavenumber
5. Absorbed frequencies are identified by peaks, indicating functional groups.

Question 7

What are the uses of infrared spectroscopy?

Answer 7

1. BREATHALYSERS
2. VEHICLE POLLUTANT EMISSIONS