Mass Spectrometry

Question 1

what can mass spectras be used for

Answer 1

to identify the molecular mass of an organic compound to find out more info about its structure

Question 2

what happens when an organic compound is placed in the mass spectrometer

Answer 2

compound loses an electron and forms a +ve ion -> the molecular ion

Question 3

what’s the molecular mas value?

Answer 3

same as mr value

Question 4

what’s the m/z value of the x axis of the graph for?

Answer 4

represents molecular mass of molecular ion/original molecule

Question 5

how to find molecular mass from a mass spectrum

Answer 5

locate molecular peak

clear peak on right side for highest m/z value

Question 6

whats the symbol for the +ve molecular ion

Answer 6

M+

Question 7

why is there a very small peak after the M+ peak?

what’s it called?

Answer 7

M+ 1 peak

it exists bcus 1.1% of carbon is present as the carbon-13 isotope

Question 8

describe fragmentation

Answer 8

when some molecular ions break down into smaller pieces known as fragments
(fragment ions)

Question 9

what are the other peaks on the mass spectrum caused by?

Answer 9

fragment ions

Question 10

what does the simplest fragmentation break molecular ions into?

Answer 10

2 species :
+vely charged fragments ions -> detected by mass spectrometer
a radical -> uncharged radicals NOT detected

Question 11

how can you tell how a molecular ion can split to form a fragment ion and racial?

Answer 11

charged part -> fragment ion
uncharged part -> radical
p.g. 253

Question 12

why is the mass spectrum of each compound unique?

Answer 12

all molecules fragment in different ways depending on their structures -> can help identify molecules even if they have the same molecular mass

Question 13

no. of carbon atoms equation

Answer 13

(height of M+1 peak) / (height of M+ peak) x 100

Question 14

define FIRST ionisation enthalpy/energy

Answer 14

energy needed to remove 1 mole of electrons (to infinity) from 1 mole of gaseous atoms to form 1 mole of gaseous 1-positive ions

Question 15

why does fragmentation occur?

Answer 15

molecular ions are unstable

Question 16

does the radial produce a line on the spectrum and why?

Answer 16

no

it’s uncharged

Question 17

whats ionisation energy?

Answer 17

attr. between electrons + protons in nucleus

a measure of amount of energy needed to remove electrons from atoms

Question 18

define a TM element

Answer 18

forms 1 or more stable ions with an incompletely filled d-shell

Question 19

what happens to TM elements first to form an ion?

Answer 19

lose s-electron shell electrons first to form an ion

Question 20

1st ionisation energy of sodium equation

Answer 20

Na (g) -> Na+ (g) + e-

Question 21

why do some elements have large differences of 1st ionisation energies?

Answer 21

if one element has an outermost electron that’s further away there’s a weaker attr. -> less energy needed

Question 22

why can 2nd ionisation energies be lower than 1st ionisation energies?

Answer 22

For 2nd there’s more shielding so less enthalpy needed to remove 2nd

Question 23

what are sub-levels know as?

Answer 23

orbitals

Question 24

state the max no. of electrons for each orbital

Answer 24

s orbitals = 2
p orbitals = 6
d orbitals = 10
f orbitals = 14

Question 25

define an orbital

Answer 25

region in space (3D) where there’s a high probability of finding an electron

Question 26

what can orbitals do if they have opposite spin?

Answer 26

hold up to 2 electrons

pauli’s exclusion principal

Question 27

which element is an exception?

Answer 27

chronium

Question 28

effective nuclear charge equation

ENC

Answer 28

no. of PROTONS in nucleus - no. of inner shell ELECTRONS