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Chemical Ideas 6.5

Chemical Ideas 6.5. Mass spectrometry. What’s inside?. In the nucleus?. Protons. And around the nucleus?. Neutrons. Electrons. Location. How are they different?. Mass. Charge. Nuclear symbols. p + n. Mass number =?. Na. 23. 11. p ( = e - ). 11 11 12. Atomic number =?. p?.

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Chemical Ideas 6.5

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  1. Chemical Ideas 6.5 Mass spectrometry

  2. What’s inside? In the nucleus? Protons And around the nucleus? Neutrons Electrons

  3. Location How are they different? Mass Charge

  4. Nuclear symbols p + n Mass number =? Na 23 11 p ( = e-) • 11 • 11 • 12 Atomic number =? p? e-? n?

  5. What are isotopes? 17 17 p? p? Cl Cl 17 17 35 37 e-? e-? 17 17 18 20 n? n? • Atoms of the same element with: • The same atomic number but different mass numbers • Same number of protons but different numbers of neutrons

  6. Why is 35Cl O.K.? Chlorine always has an atomic number of 17! Relative isotopic mass Cl Cl 37 35 17 17 Cl-37 Cl-35

  7. So what is relative atomic mass? Cl-35 75% 25% Cl-37

  8. Relative atomic mass is the average of the relative isotopic masses Cl-35 75% Cl-37 25% How do we get a relative atomic mass of 35.5?

  9. What 2 things did we need to know? Relative isotopic masses. The relative abundances.

  10. How do we find them out? Use a mass spectrometer

  11. Mass spectrometry

  12. sample inlet vacuum chamber

  13. Mg Mg+ e- e-

  14. electric field sample inlet vacuum chamber

  15. electric field flight path sample inlet Ion detector intensity vacuum chamber time measurement m/z

  16. KE = ½ mv2 • Ion 1 • KE = 16 • m = 2 • v = 4 • Ion 2 • KE = 16 • m = 8 • v = 2 • Greater the mass, the less the velocity • Greater the mass, greater the time of flight • From time of flight, mass is calculated

  17. electric field flight path sample inlet Ion detector intensity vacuum chamber time measurement m/z

  18. A mass spectrum … 100 80 60 % 40 20 m/z 35 36 37

  19. Relative atomic mass is the average of the relative isotopic masses Cl-35 75% Cl-37 25% How do we get a relative atomic mass of 35.5?

  20. CH3CO+ CH3COCH3 CH3COCH3+ CH3 e- e- e-

  21. Other fragments from propanone - CH3COCH3? CH3COCH3+ Which is the molecular ion? CH3CO+ CH3 • CH3+ • CH3CO • O • O+ • CH3C • CH3C+ Which give a peak on a mass spectrum?

  22. Name it. CH3 CH2 CH O CH2 CH3 CH3 2-ethoxybutane

  23. + Base peak? 2? Molecular ion ? 3? 1?

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