1.3 – THE CURRENT MODEL OF THE ATOM
SWBAT…
 Describe and justify the current electron-cloud model of the atom using
evidence from the double-slit experiment, Heisenberg, and Schrodinger
 Describe how the model of the atom changed through work by Dalton,
Thomson, Rutherford, Bohr, Chadwick, Heisenberg, and Schrodinger
Do Now: You do not have to answer in complete sentences. Exam prep: Six questions, six minutes.
1) If Thomson’s Plum-Pudding model of the atom was correct, what would Rutherford have observed in his gold
foil experiment?
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2) What were the two main conclusions from Rutherford’s gold foil experiment?
1. _______________________________________________________________________________________
2. _______________________________________________________________________________________
3) What problem could Rutherford’s model not explain that Bohr addressed?
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4) In Bohr’s model, photons are _____________________ when an electron transitions from a lower energy level
to a higher energy level.
5) In which letter electronic transition (labeled below) would a photon be emitted with the smallest wavelength?
6) How did Bohr’s model break down?
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The Double-Slit Experiment:
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A wave fired at a double slit will form an interference pattern
A particle fired at a double slit will form an impression
Light Fired at a double slit:
1) Will photons form an interference pattern or impressions?
Electrons fired at a double slit:
2) Will electrons form an interference pattern or impressions?
Game Changing Idea!
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Quantum particles, like ___________________ and _____________________ exhibit wave-particle duality.
o
o
Have momentum and energy like particles
Travel and behave like waves
SciShow: Heisenberg’s Uncertainty Principle
3) What two things can you not know about quantum particles at the same time?
4) What is the observer effect?
5) Does the uncertainty principle only apply when you are trying to observe particles (is it an observer effect)?
6) What property of quantum particles makes Heisenberg’s Uncertainty Principle a fundamental property?
7) Prediction: How do you think wave-particle duality and Heisenberg’s Uncertainty Principle changed the model of
the atom?
Key Points: Heisenberg’s Electron Cloud Model
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It is _______________________ to determine the exact position and momentum of an electron.
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Electrons exist as a ___________________________________________ surrounding the nucleus.
8) What is a probability?
9) What can this not explain?
Schrodinger’s Equation & Electron Orbitals:
Fun fact! As a chemistry or physics major, you will find solutions for this equation your junior year of college 
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Quantitative model predicting the energies of the electron-wave as a function of location
Used to determine the probability of electrons existing in certain regions of space
Explains how electrons remain stable (answers Rutherford’s problem)
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Electron orbitals are a region bounding the volume in which there is a _____________ probability of finding an
electron with a certain energy
o Used with current atomic emission spectra data for the majority of elements (solves Bohr’s problem)
o Helps explain properties of atoms and shapes of molecules (predictive)
Check Your Understanding
10) What was the problem with Bohr’s model?
11) What experiment and new discovery changed the way that scientists looked at electrons?
12) What does Heisenberg’s Uncertainty principle state?
13) Describe, in your own words, the electron cloud model of the atom. How is this similar to Bohr’s model? How is
it different?
THE BIG PICTURE: UNIT ONE
Enduring Understandings:
 Matter is composed of small particles called atoms.
 Atoms are so small that they are difficult to study directly; atomic models are constructed to explain experimental data on collections of atoms.
 The current model of atomic structure has changed over time and experimental evidence has led to changes in the atomic model.
 Each atom has a charged substructure consisting of a nucleus, which is made of protons and neutrons, surrounded by a cloud of electrons.
 Electrons in atoms have definite energy levels, with no values in between. When an electron moves from one energy level to another, it emits or absorbs
a photon that has equal energy to the energy difference between the levels. Consequently, each element has a unique emission or absorption spectrum.
Dalton’s Indivisible Atom:
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Atoms are indivisible building
blocks of matter
Atoms are not created or
destroyed in chemical reactions;
only rearranged
Heisenberg’s Electron Cloud Model:
Cathode Ray Tube Exp’t
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Thomson’s Plum-Pudding Model:
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Atoms have subatomic structure
Electrons are small, negatively
charged particles within atoms
Electrons are “stuck” to the atom
in a positive fluid
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Gold Foil Experiment
Rutherford’s Nuclear Model:
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Science Literacy Skill: Evaluating Scientific Models
A scientific model is…
 A representation of something we cannot see
 Explains observed phenomena
 Supported by experimental evidence
 Justified by existing accepted scientific theories
 Predictive and testable
 Developed over time
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Atoms contain a small, dense,
positively charged nucleus
surrounded by electrons
Most of the atom is empty space
Electrons exhibit wave-particle
duality
The exact location and exact
momentum of an electron can
never be known at the same time
An orbital is the enclosed region
around the nucleus there is a
90% probability of finding an
electron with a certain energy
H Emission Spectrum
Bohr’s Shell Model:
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Electrons orbit the nucleus at
discrete energy levels in
concentric circular paths
Electrons absorb or emit photons
when transitioning energy levels
The Double-Slit Exp’t
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