1. Atomic Masses/Mass Spectroscopy

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

3. Example 1: Neon has 3 natural isotopes. Ne-20 (90.51%, 19.99244 u) Ne-21 (0.27%, 20.99395 u) Ne-22 (9.22%, 21.99138 u) What is the weighted average atomic mass for Ne?

4. Remember Cathode Rays?? Electrons as cathode ray particles Additional research concluded, positive particles present in cathode……..HOW? o Opposite deflection o POSITIVE IONS formed from atoms presen t It is possible to produce a beam consisting of ONLY these positive ions

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

6. Mass Spectrometry (cont.) Ion separation can occur through the use of a magnetic field Most ions here have positive charge SO separation based on mass Chart of ion separation generated through mass spectrometer o Separates positive ions by mass/charge raio Comparison between mass spectrum of one compound to mass spectrum of standard o Enables identification of compound/atom

7. Analyzing a Mass Spectrum Peaks = o Isotope presence with corresponding mass Heights= o 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. o A) Calculate the average atomic mass of Neon based on this data. o B) Which of the peaks would be tallest? Why?

10. Other Types of Spectroscopy Infrared Spectroscopy---- o Determines structure and analyzes compounds Ultraviolet Spectroscopy---- o Molecule and ion analysis Nuclear Magnetic Resonance (NMR) Spectroscopy- --- o Organic molecular structures

11. Homework Mass Spectrometry Worksheet p. 29 #29 p. 293 #29-30