6. Robert A. Millikan
-
-
-
Fg = mg
Fe = qE
1910-Millikan oil drop
e/me = - 1.758821011 C/kg
J.J. Thomson's experiment and the
charge-to-mass ratio of the electron
Newton's first law :
SF = 0 [Forces are Balanced]
9. Mass spectrometry (MS) is an analytical technique that ionizes chemical species and sorts the ions based
on their mass-to-charge ratio. In simpler terms, a mass spectrum measures the masses within a sample.
10. The Classical/Solar system
Atomic Model is doomed
• Let’s consider atoms as a quasi sun/planet model (only
one planet so that it is just a two body problem.
• The force balance of circular orbits for an electron
“going around” a stationary nucleolus
where v is the tangential velocity of the electron. Circular motion is
accelerated, accelerated charges need to radiate energy off
according to Maxwell, loosing kinetic energy
11. Figure : A prism spectroscope can be used to observe emission
spectra (a). The emission spectra of mercury (b) and barium (c)
show characteristic lines.
12. Figure : This apparatus is used to produce the absorption
spectrum of sodium (a). The emission spectrum of sodium
consists of several distinct lines (b), whereas the absorption
spectrum of sodium is nearly continuous (c).
13. Balmer Series
• In 1885, Johann Balmer found an empirical formula for
wavelengths of the emission spectrum for hydrogen in nm within
the visible range
(where k = 3,4,5…)
• A good physical theory needs to make sense of this empirical result
There is a minimum wavelength corresponding
to a maximum frequency and energy of photons
657
nm
Red
486
Blue
434
Violet
410
397
365
nm
Series
limit
14. Rydberg Equation
• As more scientists discovered emission lines at infrared and
ultraviolet wavelengths, the Balmer series equation was extended
to the Rydberg equation, actually on the basis of this equation,
people went out looking for more lines :
(where RH = 1.096776 x 107 m-1)
Hydrogen Series of Spectral Lines
Discoverer (year) Wavelength n k
Lyman (1916) Ultraviolet 1 >1
Balmer (1885) Visible, Ultraviolet 2 >2
Paschen (1908) Infrared 3 >3
Brackett (1922) Infrared 4 >4
Pfund (1924) Infrared 5 >5
Can be applied to isotopes of hydrogen by modifying R slightly
R
m
R
e
H
1
7
2
10
09737
.
1
2
m
h
c
m
R e
a
M
m
M
m
e
e
+
Aside: