1. Mass Spectrometry

2. Dalton’s model of the atom
Stated “all atoms of an element are identical”
Not entirely true…
Same number of protons and neutrons
Different masses (due to different numbers of neutrons)
Isotopes of same element
Examples: C-12, C-13, C-14

3. Mass Spectrometry
Provided evidence that Dalton’s model is incorrect and needed modification
Any time new evidence is collected theories must be revised
Technique provides a spectra of the masses of the substances that make up a sample of a substance
X-axis: mass of substance
Y-axis: Relative abundance (% of substance with that mass)

4. Mass Spectrometry for Singular Atoms
If Dalton’s theory was correct would expect for every singular element (B, C, Na, etc.) that the mass spec. graph would only contain one line
Since all atoms of the element would have had identical masses
In reality, each isotope should have it’s own peak on the spectra

5. Mass Spectrometry for boron
What does this Mass Spectrometry Graph tell us about Boron?

6. Mass Spectrometry for boron
Number of isotopes
Mass of each isotope
Relative abundance of each isotope
Estimate of Average atomic mass
Actual Average atomic mass of boron (can be calculated)

7. Average atomic mass

8. Chlorine Diatomic (Cl2) Two groups of peaks (one set midway)
Use the midway values to determine the average atomic mass of one atom of chlorine