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RELATIVE ATOMIC MASS

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... 6_Concourse 7_Concourse Equation RELATIVE ATOMIC MASS In order to ... of atoms and molecules Relative isotopic mass Isotopes of Hydrogen ... – PowerPoint PPT presentation

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Title: RELATIVE ATOMIC MASS


1
RELATIVE ATOMIC MASS

2
In order to produce correct amount of chemicals
  • We have to know about masses of atoms and
    molecules, how these are used in chemical
    calculations.

3
Masses of atoms and molecules Relative isotopic
mass
  • Isotopes
  • Atoms with the same number of protons, but
    different numbers of neutrons.
  • Atoms of the same element (same atomic number)
    with different mass numbers (nucleon numbers).
  • Isotopes of chlorine
  • 35Cl 37Cl
  • 17 17
  • chlorine - 35 chlorine - 37

4
Isotopes of Hydrogen element
Tritium
Deuterium
has the biggest abundance in nature.
5
Relative isotopic mass
  • Is the mass of a particular isotope of an element
    on a scale where an atom of carbon-12 has a mass
    of exactly 12 units.

6
Why C-12?
  • 12C is chosen as the STANDARD atom and given
    the mass of exactly 12 units.
  • The mass of other atoms is found by comparing
    their mass w/ the mass of Carbon-12 atoms.

7
C-12 is the standard atom
  • An atom twice as heavy as one C-12 has a mass of
    24.00 (Mg24.00). An atom 12 times lighter than
    one C-12 atom is 1.00 (H1.00

8

Relative isotopic mass
  • There are three naturally occurring isotopes of
    neon (Ne)
  • 20Ne isotopic mass 19.99244018 amu
  • 21Ne isotopic mass 20.9938467 amu
  • 22Ne isotopic mass 21.9913855 amu
  • 1 atomic mass unit 1/12th of the mass of
    one carbon-12 tom.

9
To determine the relative isotopic mass values
  • an instrument called MASS SPECTROMETER is used.

10
Mass spectrums provide
  • Relative abundance of isotopes
  • m/z ratio of isotopes
  • Since the isotopes detected are 1 charged

m/z ratio isotopic mass
11
Once again, mass spectrums provide
  • Relative abundance of isotopes
  • Isotopic mass of the isotopes.

12
Relative Atomic Mass, Ar
  • is the weighted average of the masses of the
    isotopes of an element on a scale on which a
    carbon-12 atom has a mass of exactly 12 units.
  • Ar

(IM 1x its RA) (IM2 x its RA)
The sum of RA of all isotopes
IM Isotopic mass RArelative abundance
13
IMPORTANT!!!
  • Since Ar is the ratio of the average mass per
    atom of an element to 1/12th of the mass of an
    atom of the C-12 isotope, IT HAS NO UNITS!!!
  • Ar is for
  • 1 ATOM!!!

14
What mass values of atoms are given in the data
booklet?
  • Any atom with whole number Ar?
  • What does having whole number Ar mean for an
    atom?
  • It has no isotopes!!!
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