1. Atomic Masses/Mass Spectroscopy

2. How do we calculate atomic mass?
1) Masses of Isotopes
2) Fraction of the abundance of each isotope
usually a percentage
Average atomic mass = mass contributed by all isotopes
Fraction of abundance (isotope mass) = mass from a particular isotope

3. Example 1: Neon has 3 natural isotopes. Ne-20 (90. 51%, 19
Example 1: Neon has 3 natural isotopes. Ne-20 (90.51%, u) Ne-21 (0.27%, u) Ne-22 (9.22%, u) What is the weighted average atomic mass for Ne?
20.18 u

4. Remember Cathode Rays?? Electrons as cathode ray particles
Additional research concluded, positive particles present in cathode……..HOW?
Opposite deflection
POSITIVE IONS formed from atoms present
Positively charged ions also present in cathode ray tube.
Atoms bombarded with electrons electrons collide with atoms remove valence electrons produce POSITIVE IONS

5. Mass Spectrometry Technique to analyze positive ion beams
Aids in determining the mass of an atom/molecule
Ion Separation
Caused by utilization of magnetic field
Ions or compounds bombarded with electrons, ions fragment and provide unique fragmentation pattern for substance
Ions deflect from their course
Heavy ions---little deflection
Light ions—most deflection

6. Mass Spectrometry (cont.)
Most ions here have positive charge SO separation based on mass
Chart of ion separation generated through mass spectrometer
Separates positive ions by mass/charge ratio
Comparison between mass spectrum of one compound to mass spectrum of standard
Enables identification of compound/atom

7. Analyzing a Mass Spectrum
Peaks =
Isotope presence with corresponding mass
Heights=
Relative isotope abundance
** Diatomic elements—additional peaks will be present due to the masses of isotopes from individual atoms AND isotopes from paired atoms.
REMEMBER THEM

8. REFER TO WORKSHEET

9. Example 1:
The mass spectrum of Neon shows three peaks at mass/charge ratios of 20, 21, and 22 with abundances of 90.48%, 0.27%, and 9.25% respectively.
A) Calculate the average atomic mass of Neon based on this data.
B) Which of the peaks would be tallest? Why?

10. Other Types of Spectroscopy
Infrared Spectroscopy----
Determines structure and analyzes compounds
Ultraviolet Spectroscopy----
Molecule and ion analysis
Nuclear Magnetic Resonance (NMR) Spectroscopy----
Organic molecular structures
Beer-Lambert Law
Utilized to determine the concentration of a colored solution
Solution’s absorbance and concentration are directly related----MORE ON THIS TOPIC THURSDAY DURING LAB!!!