Spectroscopy

• What is the symbol of wavelength of a wave and its units

  The symbol: λ (or lambda)

  The units: metres
• What is the symbol of frequency of a wave and its units?

  The symbol: v

  The units: units s-1 or Hz
• Describe the trend of electromagnetic spectrum.


  From Radio waves to Cosmic rays:

  Wavelength decreases

  Frequency increases
• Describe the trend of visible light in the Electromagnetic spectrum.


  From the colours violet to red:

  The wavelength increases

  The frequency decreases
• Draw and label a light wave.


  An example:

  
• Define frequency of a wave.

  Its the number of complete oscillations per second.
• Define wavelength of a wave:


  The peak to peak distance between two waves
• Write an equation that links together both the frequency and wavelength of a wave:


  νλ = c

  where c is the speed of light
• What is the value of c and its units


  Value: approx 3× 10^8 in a vacuum

  units: m s^-1
• What is a limit of the wave model?


  Doesnt take account the phenomena associated with absorption and emission of radiant energy
• Describe the relation of the energy of a photon and frequency of the radiation

  The energy of the photon is proportional to the frequency of the radiation
• Write an equation linking the energy of a photon to its frequency

  E= hv

  Where h is the Planck's constant (6.628 x 10^-34 Js)

  
  

  The energy is proportional to the frequency
• Write an alternate equation of energy.

  v is equal to$1/λ$ and known to be the wavenumber

  Energy is indirectly proportional to the wavelength

  Energy is directly proportional to the wavenumber

  A) its equal to 1/λ

  
• Describe what happens when a molecule absorbs a photon.


  When a molecule absorbs a photon, the energy of the molecule increases. The molecule is promoted to an excited state

  If a molecule emits a photon, the energy of the molecule decreases.

  The lowest energy state of a molecule is known as the ground state
• How does light photons in identification in qualitative analysis?


  The substances absorb light at specific wavelengths due having certain energy level which could be used to identify the components of the sample
• Write the equations used for the involvement of light into quantitative analysis

  T=P/P0

  Where T is the transmittance (a fraction of the original light that passes through the sample) and P is the radiant power

  Another equation to use: $A=$$log(P0/P)=$$-log (T)$

  Where A is the absorbance
• Explain the value of A when there's no light.


  P=P0, then$A=$$log(1)$ which means A must be 0
• Define Beer's Law (or Beer-Lambert Law)


  Absorbance is directly proportional to concentration
• Write the equation for Beer's Law

  $A=$$\varepsilon bC$

  Where:

  b is the pathlength in cm

  C is the concentration (in M or moles $L^-1$)

  $\varepsilon$ (OR Epsilon) is the molar absorptivity with unit $M^-1$ $cm^-1$
• Define molar absorption

  The characteristic of a substance that tells us how much light is absorbed at different wavelengths
• How does light act like?

  a particle and a wave
• What is a limitation of a substance emitting and absorbing light?


  It can only emit light at wavelengths that it can absorb, i.e the range is specific
• Why is spectroscopy important?


  Using spectroscopy we can find out what a substance is and how much there is
• In Beer's law: The absorbance is proportional to concentration if: 


  1. the radiation is monochromatic,
  2. passing through a dilute solution
• The Beer's law fails to be applied if:


  The analyte undergoes a chemical change and the product of that change has a different spectrum to the original analyte