Review of Basic Atomic Structure

1. Review of Basic Atomic Structure

2. Tell me… • Basic atomic structure terminology • How to calculate average atomic mass, and why an average atomic mass exists • General ideas in Dalton’s Theory • How does mass spectrometry call into question one of the postulates?

3. Mass Spectrometry Courtesy www.lab-initio.com

4. Purpose of Mass Spectrometry • Producesspectra of masses from the molecules in a sample of material, and fragments of the molecules. • Used to determine • elemental composition of a sample • masses of particles and of molecules • potential chemical structures of molecules by analyzing the fragments • identity of unknown compounds by determining mass and matching to known spectra • the isotopic composition of elements in a molecule* • *our primary use

5. How is this implemented into the AP curriculum? • Interpreting mass spectra • Relating data to avg atomic mass & presence of isotopes • Explain how mass spec data contributes to current atomic model & presence of the neutron

6. Stages The ionizer converts some of the sample into ions. Mass analyzers separate the ions according to their mass-to-charge ratio. The detector records either the charge induced or the current produced when an ion passes by or hits a surface

7. Sample Data – finding avg. at. mass

8. Sample Question • How many isotopes are present in this element?   • Which isotope is the most abundant? • Predict the identity of this element. • Explain why this graph cannot represent neon.

9. Sample Question • Based on the mass spectrum of atom Y, which of the following statements is false? • Peak A and peak D come from atoms that have the same number of electrons • There are seven isotopes of atom Y • Peak C comes from the most abundant isotope of atom Y • Peak D comes form an atom with 4 more protons than the atom that gave peak B

10. Sample Question • The identity of atom Y is: • Zirconium • Molybdenum • Americium • Einsteinium

11. Sample Question • Which peak comes from an atom with the greatest number of neutrons? • A • All peaks in the spectrum have the same number of neutrons • C • D

12. Sample Question • Bromine exists in nature as a mixture of two isotopes, Br-79 and Br-81. The mass spectrum of bromine (Br2) consists of three peaks with the characteristics listed on the table. • How do you interpret these data?

13. Spectra of Larger Molecules Spectra of large molecules have many fragments, and the interpretation of their spectra is beyond the scope of this course. Codeine, C18H21NO3

14. Mass Spectrometry in Forensics • Mass spectrometry is used to confirm the identify of unknowns, such as illegal drugs • Unknowns are often not pure, and must be separated from a mixture • Gas chromatography is used to separate the components of the mixture • Mass spectrometry “fingerprints” the components, so that they can be matched to existing known spectra Gas Chromatograph Mass Spectrometer Mixture