Transcript The Quantum Model of the Atom

The Quantum Model of the
Atom Part 1
Electrons as Waves
The Word for the day is…
 QuantizedOnly certain specific values are allowed.
 The electron’s energy is quantized. This
means that it can only have certain specific
amounts of energy at a given time
Quantized
 What if the accelerator on your car was
quantized?
 Is it?
What do you think?
 My fingerprint looks
like this
 An Elements
fingerprint looks like
this
Atomic Emission Spectrum
 We need someone who
could make a
connection between
the atomic emission
spectrum of an element
and the model of an
atom
 And his name was
– Bohr
–Neils Bohr
How did Bohr’s model explain the
bright line spectrum produced by
hydrogen?
 When the atom absorbs energy the electron
“jumps” to a higher energy level (orbit).
 When the electron “falls” to a lower orbit the
energy is released as a photon of light.
 The color of light produced corresponds to
the size of the energy change.
 Remember this equation:
 E = hf
What type of spectrum is produced
when hydrogen emits light and why?
 A bright line or atomic emission spectrum is
produced … NOT a continuous spectrum
 The electron’s energy levels are quantized.
 Electrons can only absorb or release certain
specific amounts of energy. Thus…
…only certain specific colors, frequencies or
photons (energies) of light can be produced!
Bohr Model of the Atom
 How does the photon that is
emitted (the released energy)
correspond to the colored lines we
see in the atomic emission
spectrum?
 Lets look again at Hydrogen
Remember
Why are only certain specific colors
produced?
 Because the electron can only have certain
specific amounts of potential energy. In
other words, it is quantized!
 Thus, the electron can only absorb or
release certain specific amounts of
energy…corresponding to the specific colors
in it’s atomic emission spectrum.
HOMEWORK
 Read pages 135-137
 Answer questions #1,2 on page 140
 Look at slide #14, what is wrong with this
image?
What did Bohr’s Model Give Us
 Three important idea’s:
 1 – Electron’s exist in stable orbits about the
nucleus
 2 – Only certain orbits are allowed
 3 - An electron passing from a lower orbit to
a higher orbit must absorb light with exactly
the difference in energy between the two
orbits. Similarly, for an electron to move
from a higher orbit to a lower one, it must
emit light corresponding to exactly the
difference in energy.
What were the shortcomings of Bohr’s
model of the atom?
• Scientists did not understand why the
electron could only exist in certain specific
orbits or energy levels? (quantized)
•It worked perfectly for hydrogen (1
electron) but not for the other
elements.
Matter Waves
-The wave-like behavior of particles
Louis de Broglie
 de Broglie Hypothesis states that any moving
particle or object has an associated wave.
 For this he won the Nobel Prize in Physics in
1929
 Tiny electrons behave similar to waves
 When confined to a space, waves can only have
certain frequencies (energies). Thus, they are
quantized like electrons in Bohr’s model.
 Light has a dual (particle/wave) nature. The
electron has a dual (particle/wave) nature as well.
Lets take a look at the Double Slit
Experiment
http://www.youtube.com/watch?v=DfPeprQ7oGc
Every object has wave properties
 De Broglie wavelength equation
h

mv
 An electron that has a mass of 9.11 x 10-28 g is
traveling at 90 mi/hr
– It has a wavelength of 2 x 10-5 m measured in the IR
section
 A baseball that has a mass of 0.15 kg that is
pitched at 90 mi/hr
– It has a wavelength of 1.1 x 10-34 m, not measurable by
any instrument
Homework
 Read pg 137 – 140
 Answer question #3 on page 140
 Answer question #18 on pg 157
Heisenberg’s Uncertainty Principle
 It is impossible to determine simultaneously
the position and velocity of an electron or
any other particle.
 This is due to the fact that by observing an
electron, the measurement itself will cause
the electron to change position. Light will
interact with an electron and cause it to
move.
 The way around this problem is to describe
electron location in terms of probability of
finding the electron in certain regions in the
atom.
 Werner Heisenberg is speeding down a
highway, when he's pulled over by the police.
The cop walks up to him and says, "Excuse
me, sir, do you know how fast you were
driving?"
 Heisenberg looks up to the
officer and says,
"Nope, but I know
exactly where
I was!"
SchrÖdinger’s Wave Equation
  2  2  2
 x 2  y 2  z 2

 8 2m
  h 2  E  V  x, y, z    x, y, z   0

Memorize this equation
Just Kidding
SchrÖdinger’s Wave Equation
 Equation describes the wave properties of
electrons and other small particles.
 Proved quantization
– Only waves of specific energies and therefore
frequencies provide solutions to the equation
 Describes the arrangement of electrons in
atoms.
Together, the ideas that electrons
are quantized, the de Broglie wave
properties, the Heisenberg
uncertainty principle and the addition
of the Schrödinger wave equation
laid the foundation for the
development of the quantummechanical model of an atom.
The modern electron cloud model
(a.k.a. quantum-mechanical model)
shows electrons orbiting around
the nucleus in specific regions (or
“clouds”) based on the probability
of finding them within that region.
Yet again another modification
to the atomic model
Lets take a look back
Orbitals
 ORBITAL ≠ ORBIT
 A three dimensional region around the
nucleus that indicates the most probable
location of an electron with a given energy.
– Higher probability – higher electron density
– Lower probability – lower electron density
 There are several different types of orbitals
each having a different fundamental shape.
The 5 d orbitals
http://www.winter.group.shef.ac.uk/orbitr
on/AOs/3d/index.html
http://www.falstad.com/qmatom/