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Chemical Ideas 6.5 Mass spectrometry What’s inside? In the nucleus? Protons And around the nucleus? Electrons Neutrons.

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Presentation on theme: "Chemical Ideas 6.5 Mass spectrometry What’s inside? In the nucleus? Protons And around the nucleus? Electrons Neutrons."— Presentation transcript:

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2 Chemical Ideas 6.5 Mass spectrometry

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

4 How are they different? Mass Charge Location

5 Mass on Ar scale Charge p1+1 n10 e-e

6 Nuclear symbols Na Mass number =? Atomic number =? p + n p ( = e - ) p? e-?e-? n? 11 12

7 What are isotopes? Cl Cl p? e-?e-? n? p? e-?e-? n? Atoms of the same element with: The same atomic number but different mass numbers Same number of protons but different numbers of neutrons

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

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

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

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

12 How do we find them out? Use a mass spectromete r

13 Mass spectrometry

14 sample inlet vacuum chamber

15 Mg e-e- e-e- Mg +

16 sample inlet vacuum chamber electric field

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

18 KE = ½ mv 2 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

19 sample inlet vacuum chamber electric field flight path time measurement Ion detector intensityintensity m/z

20 A mass spectrum … % m/z

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

22 CH 3 COCH 3 e-e- e-e- e-e- CH 3 COCH 3 + CH 3 CO + CH 3

23 Other fragments from propanone - CH 3 COCH 3 ? CH 3 COCH 3 + CH 3 CO + CH 3 + CH 3 CO O O + CH 3 C CH 3 C + CH 3 Which give a peak on a mass spectrum? Which is the molecular ion?

24 CH 3 Name it. CH 3 CH 2 CHCH 2 CH 3 O 2-ethoxybutane

25 Molecular ion ? Base peak? 3? 2? 1? +

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