http://www.tutorvista.com/content/science/science-i/atoms-molecules/atom.php Relative Atomic Mass Isotopes are present Weighted average mass- due to presence of isotopes Relative Isotopic Mass, (A r ) 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 12 C x % Abundance) + (Mass 13 C 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
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IB Chemistry on Mass Spectrometry and Isotopes for Option A SL/HL.
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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%
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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
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
• 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
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-
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
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