Download Electron Arrangement and Atomic Emission Spectra

Atomic Structure 3
Electron Arrangement and Atomic Emission Spectra
IB Topic 2.3
http://english.turkcebilgi.com/Sodium+vapor+lamp
1
The Road to the Structure of the Atom
The Rutherford Model
http://astronomy.nmsu.edu/nicole/teaching/dste110/lectures/lecture18/slide01.html
• the atom is mostly empty space
• the nucleus is very small and
positively charged
• electrons are found in the region
around the nucleus
What theoretical challenge is
presented by this model?
http://tap.iop.org/atoms/duality/507/page_47057.html
2
The Road to the Structure of the Atom
TOK Connection: A paradigm shift ... the rules change!
A new way of looking at the physics of atoms is needed.
Good bye Newtonian Physics - Hello Quantum Physics.
“We are all agreed that your theory is crazy.
The question which divides us is whether it is crazy enough to have a chance of being correct.
My own feeling is that it is not crazy enough.”
Niels Bohr to Wolfgang Pauli
3
The Road to the Structure of the Atom
To address the question of why
electrons do not spiral into the
nucleus, Niels Bohr proposed that
the energy of electrons in an atom
is quantized.
This means that electrons are only
allowed to have certain defined
(or discrete) values of energy.
Therefore, electrons may only exist in defined energy levels
around the nucleus. They would not spiral into the nucleus.
4
The Bohr Model - Quantized Electrons
An analogy for quantized electrons:
5
The Bohr Model - Evidence
On what empirical (experimental) evidence did Bohr base
his proposal of energy levels in atoms?
http://www.green-planet-solar-energy.com/atomic-emission-spectrum.html
atomic emission spectra
6
The Bohr Model - Evidence
Electromagnetic Radiation Returns!
violet light
short wavelength
high energy
http://www.antonine-education.co.uk/physics_gcse/Unit_1/Topic_5/topic_5_what_are_the_uses_and_ha.htm
red light
long wavelength
low energy
7
The Bohr Model - Evidence
Spectroscopes
A spectroscope is used to analyze the light emitted from a substance.
It DISPERSES incoming light into its component wavelengths.
In this way, you may think of the spectroscope as acting like a prism.
white light viewed in a
spectroscope
neon light viewed in a
spectroscope
8
The Bohr Model - Evidence
two types of visible light spectra:
A light source that produces a
continuous spectrum suggests
that the source emits all
energies of visible light.
http://ausgo.aao.gov.au/IYAcontest/news.html
A light source that produces a
line spectrum suggests that the
source emits only certain discrete
energies of visible light.
AKA:
discrete (or line) spectrum
9
The Bohr Model - Evidence Lab Activity
Atomic Emission Spectra Activity
Flame Tests!
Complete the activity and
discuss the questions with your group members.
10
The Bohr Model - Evidence
How do atoms emit light?
Atomic Emission Spectrum Animation
e– must move up to a
higher energy level
less energy
absorb
energy
ground state atom
(all e– in the lowest
possible energy level)
more energy
excited state atom
(unstable)
e– fall down to lower
energy levels, releasing light
with different energy values
11
The Bohr Model - Evidence
Formation of the Line Spectrum in Hydrogen
In the visible light spectrum, energized electrons fall to n=2.
12
The Bohr Model - Evidence
Formation of the Line Spectrum in Hydrogen - Check
VB
400
G
R
500
600
700
(nm)
To which energy level do electrons fall in the visible light emission spectrum of
hydrogen?
Which electron transition gives the red line?
Which electron transition gives the blue line?
Compare the energy of these two electron transitions (i.e. red vs blue light
emission.)
13
The Bohr Model - Evidence
Formation of the Line Spectrum in Hydrogen - Check
VB
400
G
R
500
600
700
(nm)
To which energy level do electrons fall in the visible light emission
spectrum of hydrogen?
Which electron transition gives the red line?
Which electron transition gives the blue line?
Compare the energy of these two electron transitions.
Why is there no yellow line in this emission spectrum?
14
The Bohr Model - Evidence
Three Series of Atomic Emission Spectra for Hydrogen
Balmer series
visible (intermediate E)
electrons fall to n=2
Paschen series
infrared (lower E)
electrons fall to n=3
Lyman series
ultraviolet (higher E)
electrons fall to n=1
http://www.avogadro.co.uk/light/bohr/spectra.htm
15
The Bohr Model - Evidence
Three Series of Atomic Emission Spectra for Hydrogen
Compare the energy of the lines in the Lyman series
and the Paschen series.
Explain the difference in the energy released in the Lyman
series and the Paschen series.
16