1. Spectroscopy
Chapter 7

2. The electromagnetic spectrum
All forms of spectroscopy use a part of the electromagnetic spectrum to give us information about the materials around us.
Electromagnetic radiation interacts with atoms and molecules.
The nature of this interaction depends upon the energy of the electromagnetic radiation.

3. Spectroscopy
Various spectroscopic techniques provide us with information about:
The type of atom of molecule that is present
How much of a particular atom or molecule is present
The structure and bonding of the molecule.

4. Spectroscopy Spectroscopy techniques utilise the fact that:
Atoms or molecules absorb and emit electromagnetic radiation of specific energies
Atoms and molecules undergo a change when they absorb electromagnetic radiation
Different parts of the electromagnetic spectrum affect different parts of the atom or molecule

5. Energy
In each of the spectroscopic techniques we will look at this chapter, the atom or molecule absorbs a specific quantum of energy which causes the atom or molecule to move to a higher energy level.
With atoms we look at the movement of electrons to higher energy levels.

6. Energy
With molecules, as well as the movement of electrons to high energy levels
We observe the movement of molecules to higher
Vibrational
Rotational
Nuclear spin
Energy levels

8. Analysis of Atoms
The following 3 techniques that use radiation from the visible region of the electromagnetic spectrum to give us information about the elements present in a sample.
Flame tests
Emission Spectroscopy
Absorption absorption spectroscopy

9. Flame Tests A simple form of qualitative analysis
Identifies certain atoms in a compound.
Atoms of different elements have different electron arrangements and hence different capacities to absorb and emit electromagnetic radiation

10. How Flame Tests Work
When atoms become excited, by heating, they absorb energy as electrons move to higher energy levels, further from the nucleus.
Excited atoms emit energy as electrons return to lower energy levels, closer to the nucleus. This energy is emitted in the form of photons of light.
These photons correspond to a particular wavelength.
The unique electron arrangement of each metal means it produces a unique flame colour.

11. Atomic Emission Spectroscopy
Turn to page 80
As a class we are going to read.
Also don’t forget ROYGBIV
Then it is your turn
Page 81
Question 3
Page 106
Question 20

12. Atomic Absorption Spectroscopy
Atomic Spectroscopy is:
One of the most widely used modern instrumental techniques
An Australian invention
Very versatile, being capable of detecting over 70 elements
Extremely sensitive, detecting concentrations of elements as part per million (ppm) levels or, in some cases, part per billion (ppb)

13. AAS AAS can be used to: Measure the amount of mercury in fish
Detect toxic metals such as copper in blood
Test urine and blood to detect an excess or deficiency of metals
Environmental sampling
Soil sampling

14. How does AAS work
Atoms will absorb light if the energy of the light is exactly that required to promote an electron from its normal energy level to a higher energy level
Each element has its own absorption spectrum
Each element to be analysed requires its own light source that will emit light of the correct wavelength

15. AAS

16. How does AAS work?
A solution of the sample to be analysed is sprayed into a flame
It is converted into atomic vapour
Light containing the chosen wavelength is passed through the flame
Atoms of the element being analysed that are present absorb some of the radiation
The light beam is then passed through a filter (monochromator) to select for the light of the chosen wavelength
Its intensity is measured by an elecrontronic detector

17. Interpreting atomic absorption spectra
Worked Example 7.3 on page 83

18. Your Turn
Page 84
Question 5
Page 106
Question 23 and 24

19. UV-Visible Spectroscopy
Makes use of the fact that many substances absorb light of characteristic wavelengths
The wavelengths of the light absorbed by compounds can be useful for their identification

20. UV-Visible Spectroscopy
Whereas Flame Emission and AAS require that the sample being analysed is sprayed into a flame, UV-visible spectroscopy involves the sample, in aqueous solution, being placed in a glass holder.
Ultraviolet or visible light at a wavelength strongly absorbed by the species being analysed for, is passed through the solution and the amount of light absorbed is directly related to the amount of that species present in the sample

21. UV-Visible Spectroscopy
When a substance absorbs visible light, it appears coloured.
The colour observed is the compliment of the absorbed colour because this is what remains to reach our eyes.
Visible spectrum
Of chlorophyll

22. UV-Visible Spectroscopy Applications
Although it can be useful for qualitative analysis. UV-visible spectroscopy is usually used for determining concentration of a substance in a sample
The procedure involves recording the spectrum of the pure substance and selecting a wavelength at which the substance absorbs strongly but other components of the sample do not.
The absorbance of the sample is then measured at this wavelength and compared to the absorbance of a series of standard solutions.

23. Uses
Clinical analysis, such as the haemoglobin content and sugar levels in blood
Determining the amount of coloured dyes in plastics
In qualitative analysis of DNA and proteins in the field of molecular biology
Determining the levels of nutrients, additives and contaminants in water and foods.

24. UV-Visible Spectroscopy
The substance to be analysed is place in a special vial.
A reference cell must be used which contains pure solvent. This is used to compensate from any reflection, scattering or absorbance of the light by the solvent.

25. Interpreting ultraviolet-visible spectra
To interpret spectra’s from UV-visible spectrometry the absorbance by a series of standard solutions is measured and a calibration graph is drawn.
The graph shows absorbance on the y-axis and concentration on the x-axis
If the absorbance of an unknown solution is known we can use this to find the concentration.

26. Worked Example 7.4
Page 87

27. Your Turn Page 88 Questions 6-8 and 12 Pg 106-107
Question 23, 24 and 26