Chemical Ideas 2.1. - University of York

Chemical Ideas 2.1. - University of York

Chemical Ideas 6.5 Mass spectrometry Whats inside? In the nucleus? And around the nucleus? Electrons Protons Neutrons

Location Mass How are they different? Charge Mass on Ar scale Charge

p 1 +1 n 1 0 e-

0.00055 -1 Nuclear symbols Mass number =? p+n 23 11 Atomic number =? Na

p? 11 e-? 11 n? 12 p ( = e -) What are isotopes? p? 35 17 Cl 17

e-? 17 n? 37 17 18 Cl p? 17 e-? 17 n? 20 Atoms of the same element with:

The same atomic number but different mass numbers Same number of protons but different numbers of neutrons Why is Cl O.K.? 35 Relative isotopic mass 35 17 Cl

Cl-35 Chlorine always has an atomic number of 17! 37 17 Cl Cl-37 So what is relative atomic mass?

Cl-35 75% 25% Cl-37 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? What 2 things did we need to know? Relative isotopic masses. The relative abundances. How do we find them

out? Use a mass spectromete r Mass spectrometry sample inlet vacuum chamber e-

Mg Mg+ electric field sample inlet vacuum chamber electric field flight path sample

inlet Ion detector vacuum chamber time measurement i n t e n s i

t y m/z KE = mv Ion 1 KE = 16 m=2 v=4

2 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 electric field flight path sample inlet Ion detector vacuum chamber time measurement i n

t e n s i t y m/z A mass spectrum 100 80 %

60 40 20 35 36 37 m/z 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? CH CH3CO+ CH CH33COCH

COCH33+ 3 e- Other fragments from propanone CH3COCH3? CH3COCH3 + CH3CO+ CH3+ CH3CO O O+ CH3C CH3C+

CH3 Which is the molecular ion? Which give a peak on a mass spectrum? Name it. CH3

CH2 CH O CH2 CH3 2-ethoxybutane CH3 This is the mass spectrum for 2-ethoxybutane;

15 CH3 14 CH2 13 CH 16 O 14 CH2

15 CH3 + 15 CH3 2? 3? Base peak? Molecul

ar ion ? 1?

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