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Relative Atomic Mass Isotopes are present

Weighted average mass- due to presence of isotopes

Relative Isotopic Mass, (Ar) of an element: •Relative isotopic mass = Average mass of one atom of element 1/12 x mass of one carbon-12 • Relative isotopic mass, carbon = 12.01

Video on Isotopes

RAM = 12.01

Relative Abundance 98.9% 1.07%

13

Why RAM is not a whole number?

Relative Isotopic Mass: = (Mass 12C x % Abundance) + (Mass 13C x % Abundance) = (12 x 98.9/100) + (13 x 1.07/100) = 12.01

Video on weighted average Weighted average calculation

Video on Isotopes

RAM calculation

12

Mg - 3 Isotopes

24 Mg – (100/127.2) x 100% - 78.6% 25 Mg – (12.8/127.2) x 100% - 10.0% 26 Mg – (14.4/127.2) x 100% - 11.3%

Relative Isotopic Mass: = (Mass 24Mg x % Abundance) + (Mass 25Mg x % Abundance) + (Mass 26Mg x % Abundance) = (24 x 78.6/100) + (25 x 10.0/100) + (26 x 11.3/100) = 24.30

Relative Abundance % Abundance

Pb - 4 Isotopes

204Pb – (0.2/10) x 100% - 2% 206Pb – (2.4/10) x 100% - 24% 207Pb – (2.2/10) x 100% - 22% 208Pb – (5.2/10) x 100% - 52%

Relative Isotopic Mass = (Mass 204Pb x % Abundance) + (Mass 206Pb x % Abundance) + (Mass 207Pb x % Abundance) + (Mass 208Pb x % Abundance) = (204 x 2/100) + (206 x 24/100) + (207 x 22/100) + (208 x 52/100) = 207.20

Convert relative abundance to % abundance

Convert relative abundance to % abundance

Relative Abundance % Abundance

Relative Isotopic Mass

Radioactive isotopes Half-life

Uranium 238 4.5 x 109

Carbon-14 5.7 x 103

Radium-226 1.6 x 103

Strontium-90 28 years

Iodine-131 8.1 days

Bismuth-214 19.7 minutes

Polonium-214 1.5 x 10-4

Isotopes

Stable Isotopes Unstable Isotopes

Unstable Isotopes – emits radiation

RADIOISOTOPES

Simulation isotope 12C, 13C, 14C

Radioisotopes •Half-life – time taken for conc/amt isotope to fall to half of its original value. •Half life decay – always constant

Shorter half-life More unstable, decay fast

Long half-life More stable, decay slowly

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Emit radiation form unstable isotope

Simulation isotope 1H, 2H, 3H

Video on Half life

Simulation half life C-14/uranuim

Half-life

Radiocarbon/carbon dating

• Half life C-14 = 5730 years • Beta (β/electron ) decay

Carbon -14

Abundance – trace amt (Unstable , radioactive)

How is form? • C-14 produce in stratosphere when…… neutron hit a nitrogen atom to form C-14 •C-14 to N-14 by converting neutron proton (proton stay in nucleus), electron emit as β radiation • emit as β ray.

(proton in nucleus – increase proton number)

emit as β ray. •Ratio C14/C12- constant if alive – TAKE in C14 (C12 constant) •Ratio C14/C12- drop if dead - NOT taking C14. (C12 constant)

Video on C-14 Carbon Dating Video on C-14 Carbon Dating/Fossil Video on C-14 Half life Carbon Dating

Simulation C-14 (Half life) At 100% (Starting)

Simulation C-14 (Half life) At 50% (Starting)

Video on Radiocarbon dating

Click to view simulation

How Radiocarbon dating works?

Carbon – 3 Isotopes Radiocarbon/carbon dating

• Half life C-14 = 5730 years • Beta (β/electron ) decay

Conclusion Ratio C14/C12 is constant is organism alive

Ratio C14/C12 drop organism die

Uses • Age dead organic material/fossil contain Carbon element • Max age limit is 60,000 years old.

Carbon -12 Carbon -14 Carbon -13

Abundance – 99% (Stable) Abundance – 1% (Stable) Abundance – trace amt (Unstable , radioactive)

How is form? • C-14 produce in stratosphere when….. neutron hit a nitrogen atom to form C-14 •C-14 to N-14 by converting neutron proton (proton stay in nucleus), electron emit as β radiation • emit as β ray.

(proton in nucleus – increase proton number)

emit as β ray. •Ratio C14/C12- constant if alive – TAKE in C14 (C12 constant) •Ratio C14/C12- drop if dead - NOT taking C14. (C12 constant)

How it is form?

Mass Spectrometer

Uses mass spectrometer

Presence of isotopes and its abundance

Relative atomic mass of an element

Relative Molecular mass of a molecule

Structure of organic compound Distinguish between structural isomers

CH3CH2CH2OH OH | CH3CHCH3

CH3 | CH3C-CH3

| CH3

CO2

structural

formula

Organic structure determination

Mass Spectrometer

Parts of Mass Spectrometer

Sample injection

Vaporization Chamber • Sample heat to vapour state

Ionization Chamber • Molecule bombard with electrons form positive ions

Accelerator Chamber • M+ ions accelerated by Electric field

Deflector • M+ ions deflected by magnetic field

Detector • Convert abundance of M+ ions to electrical current. • M+ ions neutralize by electrons (more e needed - higher current – higher intensity of peak) • Intensity of peak show -relative abundance of ions

Sample X bombarded by electron • Form positive M+ ion • Accelerated (Electric Field) • Deflected (Magnetic Field) and Detected X + e- → X+ + 2e-

Vaporization Ionization Accelerator Deflector Detector 3 2 1 5 4

2

1

3 4

Click here notes from chemguide Detail notes from chem msu

5

Mass Spectrometer

Parts of Mass Spectrometer

Vaporization Ionization Accelerator Deflector Detector 3 2 1 5 4

Click here for simulation

Vaporization Injection/ vaporization of sample liquid state gaseous

Ionization

• Form radical cations, M+

Acceleration

• M+ ions accelerated by Electric field

Deflection

• M+ ion deflected by magnetic field

Deflection depend: •mass/charge (m/z) ratio: (m/z) ratio HIGH↑ - Deflection LOW↓

Deflection depend: • mass/charge (m/z) ratio: (m/z) ratio LOW↓- Deflection HIGH ↑

37CI+

35CI+

35CI2+

2

3 4

1 5 Detector

• Convert abundance of M+ ions to electrical current. • M+ ion neutralize by electrons (more e needed - higher current – higher intensity of peak) • Intensity of peak show -relative abundance of ions

Excellent Online Spectra Database. Click here to view

Mass Spectra Online Database

1 Search methane molecule, CH4

Video on mass spectrometer

Mass/charge m/z Relative

abundance

Isotopic peak M+ + 1 Molecular ion peak, M+

2 Fragmentation pattern CH4 3 Mass Spectrum CH4

Video Ionization/fragmentation Video how MS works Video Mass spectrometer Video how MS works

Mg - 3 Isotopes

26 Mg - 11.3% - m/z highest – deflect LEAST 25 Mg - 10.0% 24 Mg – 78.6% - m/z lowest – deflect MOST

Relative Isotopic Mass: = (24Mg x % Ab) + (25Mg x % Ab) + (26Mg x % Ab) = (24 x 78.6/100) + (25 x 10.0/100) + (26 x 11.3/100) = 24.30

Using Mass spectrometry to determine Relative Isotopic Mass

Deflect MOST Deflect LEAST

Pb - 4 Isotopes

208Pb – 52% - m/z highest – deflect LEAST 207Pb - 22% 206Pb - 24% 204Pb – 2% - m/z lowest – deflect MOST

Relative Isotopic Mass = (204Pb x % Ab) + (206Pb x % Ab) + (207Pb x % Ab) + (208Pb x % Ab) = (204 x 2/100) + (206 x 24/100) + (207 x 22/100) + (208 x 52/100) = 207.20

Deflect MOST Deflect LEAST

CI - 2 Isotopes

37 CI – 24.5% - m/z highest – deflect LEAST 35 CI – 75.5% - m/z lowest – deflect MOST

Relative Isotopic Mass: = (35CI x % Ab) + (37CI x % Ab) = (35 x 75.5/100) + (37 x 24.5/100) = 35.5

Using Mass spectrometry to determine Relative Isotopic Mass

Deflect MOST Deflect LEAST

Br - 2 Isotopes

81Br – 49.3% - m/z highest – deflect LEAST 79Br – 50.6% - m/z lowest – deflect MOST

Deflect MOST Deflect LEAST

35CI 37CI

35CI 37CI

Relative Isotopic Mass: = (79Br x % Ab) + (81Br x % Ab) = (79 x 50.6/100) + (81 x 49.3/100) = 79.9

79Br 81Br

79Br 81Br

H - 3 Isotopes

3H – trace amt 2H – 0.015% - m/z highest – deflect LEAST 1H – 99.9% - m/z lowest – deflect MOST

Relative Isotopic Mass: = (1H x % Ab) + (2H x % Ab) = (1 x 99.9/100) + (2 x 0.015/100) = 1.007

Using Mass spectrometry to determine Relative Isotopic Mass

Deflect MOST Deflect LEAST

C - 3 Isotopes

14C- trace amt

13C – 1.1% - m/z highest – deflect LEAST 12C – 98.9% - m/z lowest – deflect MOST

Deflect MOST Deflect LEAST

1H 2H

1H 2H

Relative Isotopic Mass: = (12C x % Ab) + (813Cx % Ab) = (12 x 98.9/100) + (13 x 1.1/100) = 12.01

12C 13C

12C 13C

3H

14C

Ionization forming M+

CH3CH2CH2 : CH3 + e → CH3CH2CH2+.CH3 + 2e

• Fragmentation of M+ producing 43 CH3CH2CH2

+·CH3 → CH3CH2CH2+ + ·CH3

• Fragmentation of M+ producing 15 CH3CH2CH2

+·CH3 → CH3CH2CH2· + +CH3

Ionization and Fragmentation Process- CH3CH2CH2CH3

Ionization Process - CH3CH2CH2CH3

• Bombarded by electron form cation

• Molecular ion, M+ = 58 • (CH3CH2CH2CH3)+ = 58

Fragmentation Process CH3CH2CH2CH3 • Molecular ion, M+ undergo fragmentation • Cation and Radical form • Cation - Detected • Radical –Not detected (No charged)

H H

| | CH3CH2CH2 C:H + e → CH3CH2CH2 C

+.H + 2e | | H H

Ionization forming M+

CH3CH2:CH2CH3 + e → CH3CH2+·CH2CH3 + 2e

• Fragmentation of M+ producing 29 CH3CH2

+·CH2CH3 → CH3CH2+ + .CH2CH3

Ionization M+, m/z = 58

CH3CH2CH2CH3 + e → CH3CH2CH2CH3

+ + 2e

Ionization and Fragmentation of M+ • Form - m/z = 58, 43 and 15

m/z = 58

m/z = 43

m/z = 15

Ionization and Fragmentation of M+ • Form- m/z = 58 and 29

m/z = 58

m/z = 58

m/z = 29

Ionization and Fragmentation

Unpair electron Positively charged

Will MOVE (ACCELARATED) NOT move

CH3CH2CH2CH3

CH3CH2CH2CH3+- 58 - m/z highest –deflect LEAST

CH3CH2CH2+ – 43

CH3CH2+ – 29

CH3+ –15 - m/z lowest– deflect MOST

Mass spectrometry - Ionization/ Fragmentation pattern for CH3CH2CH2CH3

Deflect MOST Deflect LEAST

CH3CH2CH2CH3+

CH3CH2CH2+

Ionization

CH3+

CH3+

Ionization and Fragmentation Process

Fragmentation

Ionization of CH3CH2CH2CH3

CH3CH2CH2CH3 + e → CH3CH2CH2CH3+ + 2e → 58

or CH3CH2:CH2CH3 + e → CH3CH2

+·CH2CH3 + 2e → 58

Mass spectrum CH3CH2CH2CH3 Ionization CH3CH2CH2CH3

CH3CH2+

CH3CH2CH2CH3+

Fragmentation of M+ CH3CH2CH2

+·CH3 → CH3CH2CH2+ - 43

CH3CH2

+·CH2CH3 → CH3CH2+ – 29

CH3CH2CH2

+·CH3 → +CH3 - 15

CH3CH2CH2CH3+- 58 - m/z highest –deflect LEAST

CH3CH2CH2+ - 43

CH3CH2+ – 29

CH3+ –15 - m/z lowest– deflect MOST

CH3CH2CH2OH

CH3CH2CH2OH+- 60 - m/z highest –deflect LEAST CH2CH2OH+ – 45 CH2OH+ - 31 CH3CH2

+ – 29 CH3

+ - 15 - m/z lowest– deflect MOST

Mass spectrometry - Ionization/ Fragmentation pattern for CH3CH2CH2OH

Deflect MOST Deflect LEAST

CH3CH2CH2OH+

Ionization

CH3 +

CH3+

Ionization and Fragmentation Process

Fragmentation

Ionization of CH3CH2CH2OH

CH3CH2CH2OH + e → CH3CH2CH2OH+ + 2e → 60 or CH3CH2CH2OH + e → CH3CH2

+. CH2OH + 2e → 60

Mass spectrum CH3CH2CH2CH3 Ionization CH3CH2CH2OH

CH3CH2+

CH3CH2CH2OH+

Fragmentation of M+ CH3

+.CH2CH2OH→ +CH2CH2OH - 45

CH3CH2

+·CH2OH→ +CH2OH – 31

CH3CH2

+·CH2OH→ CH3CH2+ – 29

CH3

+.CH2CH2OH→ +CH3 - 15

CH2CH2OH+ CH2OH+

15 60

CH3CH2CH2OH+- 60 - m/z highest – deflect LEAST CH2CH2OH+ – 45 CH2OH+ - 31 CH3CH2

+ – 29 CH3

+ –15 - m/z lowest– deflect MOST

15 60

CH3CH(CH3)CH2CH3+- 72 - m/z highest –deflect LEAST

CH3CH(CH3)CH2+ – 57

CH3CH(CH3)+ - 43 CH3CH2

+ – 29 CH3

+ –15 - m/z lowest– deflect MOST

Mass spectrometry - Ionization/ Fragmentation pattern CH3CH(CH3)CH2CH3

Deflect MOST Deflect LEAST

CH3CH(CH3)CH2CH3+

Ionization

CH3+

CH3+

Ionization and Fragmentation Process

Fragmentation

Ionization of CH3CH(CH3)CH2CH3

CH3CH(CH3)CH2CH3 + e → CH3CH(CH3)CH2CH3 + + 2e → 72 or CH3CH(CH3)CH2CH3 + e → CH3CH(CH3)CH2

+.CH3+ 2e → 72 or CH3CH(CH3)CH2CH3 + e → CH3CH(CH3)+.CH2CH3 + 2e → 72

Mass spectrum CH3CH(CH3)CH2CH3 Ionization CH3CH(CH3)CH2CH3

Fragmentation of M+

CH3CH(CH3)CH2+ - 57

CH3CH(CH3)+ – 43

CH3CH2+ – 29

CH3+ - 15

CH3CH(CH3)+

15

CH3CH(CH3)CH2+

CH3CH(CH3)CH2CH3+

CH3CH2+

CH3CH(CH3)CH2CH3+

CH3CH(CH3)CH2CH3+- 72 - m/z highest –deflect LEAST

CH3CH(CH3)CH2+ – 57

CH3CH(CH3)+ - 43 CH3CH2

+ – 29 CH3

+ –15 - m/z lowest– deflect MOST

C(CH3)4+ - 72 - m/z highest –deflect LEAST

C(CH3)3+ – 57

C(CH3)2+ - 42

C(CH3)+ – 27 CH3

+ –15 - m/z lowest– deflect MOST

Mass spectrometry - Ionization/ Fragmentation pattern C(CH3)4

Deflect MOST Deflect LEAST

C(CH3)4+

Ionization

CH3+

CH3+

Ionization and Fragmentation Process

Fragmentation

Ionization of C(CH3)4

C(CH3)4 + e → C(CH3)4

+ + 2e → 72

Mass spectrum C(CH3)4 Ionization C(CH3)4

C(CH3)3+

C(CH3)4

C(CH3)2+

C(CH3)+

(C(CH3)4)+ - 72 - m/z highest –deflect LEAST (C(CH3)3)+ – 57 (C(CH3)2)+ - 42 (C(CH3))+ – 27 CH3

+ –15 - m/z lowest– deflect MOST

Fragmentation of M+

(C(CH3)3)+ – 57 (C(CH3)2)+ - 42 (C(CH3))+ –27 CH3

+ –15

(C(CH3)4)+

CI2molecule

37CI-37CI - 74 - m/z highest – deflect LEAST 35CI-37CI –72 35CI-35CI –70 37CI –37 35CI –35 - m/z lowest– deflect MOST

Mass spectrometry - Ionization/ Fragmentation pattern for molecule CI2

Deflect MOST Deflect LEAST

35CI-35CI+

35CI+

35CI-37CI+

37CI-37CI+

Ionization

37CI+

35CI+

37CI-37CI+

Ionization and Fragmentation Process

Fragmentation

Fragmentation of CI2+ into CI+

CI+.CI → [35CI+ + 35CI·] + 2e –35 CI+.CI → [37CI+ + 37CI·] + 2e –37

Ionization of CI2 to CI2+

CI:CI + e- → [35CI+.35CI] + 2e – 70 CI:CI + e- → [35CI+.37CI] + 2e – 72 CI:CI + e- → [37CI+.37CI] + 2e – 74

m/z = 37

m/z = 35

Ratio (35CI : 37CI) - 3:1

Mass spectrum CI2 / CI atoms

Ratio (35CI35CI: 35CI37CI: 37CI37CI) - 9:6:1

Ionization CI2 molecule

37CI-37CI - 74 - m/z highest – deflect LEAST 35CI-37CI –72 35CI-35CI –70 37CI –37 35CI –35 - m/z lowest– deflect MOST

Br2molecule

81Br-81Br - 162 - m/z highest – deflect LEAST 79Br-81Br –160 79Br-79Br –158 81Br –81 79Br –79 - m/z lowest– deflect MOST

Deflect MOST Deflect LEAST

79Br-79Br+

79Br+

79Br-81Br+

81Br-81Br+

Ionization

81Br+

79Br+

81Br-81Br+

Ionization and Fragmentation Process

Fragmentation

Fragmentation of Br2+ to Br+

Br+.Br → [81Br+ + 81Br·] – 81 Br+.Br →[79Br+ + 79Br·] – 79

Ionization of Br2 to Br2+

Br:Br + e- → [81Br+.81Br] + 2e – 162 Br:Br + e- → [79Br+.81Br] + 2e – 160 Br:Br + e- → [79Br+.79Br] + 2e– 158 m/z = 79

m/z = 81

Ratio (79Br : 81Br) - 1:1

Mass spectrum Br2 / Br atoms

Ratio (79Br79Br: 79Br81Br: 81Br81Br) – 1:2:1

Ionization Br2 molecule

81Br-81Br - 162 - m/z highest – deflect LEAST 79Br-81Br –160 79Br-79Br –158 81Br – 81 79Br – 79 - m/z lowest– deflect MOST

Mass spectrometry - Ionization/ Fragmentation pattern for molecule Br2