NAME:___________________________________ DATE:_______CLASS_____LAB_____
Jump Up and Get Down
Background:
At the end of 19th century, physicists knew there were electrons inside atoms, and that the
wiggling of these electrons gave off light and other electromagnetic radiation. But there was still
a curious mystery to solve. Physicists would heat up different elements until they glowed, and
then direct the light through a prism...
I've done that with sunlight. You see the whole rainbow because the prism breaks the light into
all of its separate colors.
That's what you get with light from the sun. But when scientists looked at the light coming off of
just one element, hydrogen for instance, they didn't see the whole rainbow. Instead they just got
bright lines of certain colors.
Each type of atom gives off a unique set of colors. The colored lines (or Spectral Lines) are a
kind of "signature" for the atoms.
This technique is so reliable that scientists can tell what elements they are looking at just by
reading the lines. Spectroscopy is the science of using spectral lines to figure out what
something is made of. That's how we know the composition of distant stars, for instance.
To explain the spectral line puzzle, Bohr came up with a radical model of the atom which had
electrons orbiting around a nucleus.
In order to explain the "signature colors," Bohr came up with an extraordinary rule the electrons
had to follow: Electrons can only be in "special" orbits. All other orbits just were not possible.
They could "jump" between these special orbits, however, and when they jumped they would
wiggle a little bit... And that would cause radiation!
This energy released is bursts of visible light. We call these bursts photons.
But when we played with the orbits earlier, we saw that just about any orbit and any speed is
possible. It doesn't make sense that only some orbits would be "allowed."
Now you can see why the Bohr model was considered so radical! It said that energy could only
change in little jumps. These are called quanta and that's why this kind of physics is called
Quantum Mechanics.
Each color of light has its own specific wavelength
(measured in nanometers). Here is the range of colors and
their corresponding wavelengths. Wavelengths which fall
before violet are called ultraviolet and humans cannot see
them, and wavelengths which fall after red are called
infrared and humans cannot see them.
Color
Wavelength (nm)
Violet
380-435
Blue
435-500
Cyan
500-520
Green
520-565
Yellow
565-590
Orange
590-625
Red
625-740
Procedure:
Using the color chart and the individual line spectra data for each element plot out the bright line
spectrum on the scale.
1)
Line
1
2
3
4
5
6
7
Unknown Element A
Wavelength (nm)
383
388
397
410
434
486
656
Color
2)
Unknown Element B
Line
Wavelength (nm)
1
410
2
434
Color
3)
Line
Boron
Wavelength (nm)
1
412
2
419
3
449
4
450
5
510
6
608
7
703
Color
4)
Unknown Element C
Line
Wavelenght (nm)
1
447
2
471
3
492
4
502
5
587
6
667
Color
5)
Unknown Element D
Line
1
2
3
4
5
6
7
Wavelength (nm)
405
408
435
Color
491
546
577
579
6)
Lithium
Line
Wavelength (nm)
1
413
2
460
3
540
4
670
Color
7)
Neon
Line
Wavelength (nm)
1
540
2
585
3
588
4
603
5
607
6
616
7
622
8
627
9
633
10
638
11
640
12
651
13
660
14
692
15
703
Color
Questions:
1) Which unknown element best matches with this bright line spectra for sodium?
____________________
2) Which unknown element best matches with this bright line spectra for mercury?
____________________
3) Which unknown element best matches with this bright line spectra for helium?
_____________________
4) Which unknown element best matches with this bright line spectra for hydrogen?
_____________________
5) Which of the give elements match this spectral pattern.
_____________________
6) Why are bright line spectra able to be used to identify and element?
Reflection:
The diagram below shows bright-line spectra of selected elements.
A) Identify the two elements in the unknown spectrum.
________________
and
_________________
B) Explain how a bright-line spectrum is produced, in terms of excited state, energy transitions,
and ground state. [2]