Download Station 2: Atomic Models

Parts of an Atom
Atom – are the fundamental particles of matter.
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Means “uncuttable”, are about 1/10 of a billionth of a meter across.
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Are composed of protons (p+), neutrons (nº) and electrons (e-)
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Neutrons and protons are located in the center (nucleus)
Atoms are mostly empty space
- if an electron were basketball sized, the nucleus would be a car 20 miles
away.
Proton – means “first”
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Relatively large, have a positive charge.
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The # of protons in the nucleus determines what element the atom is (a.k.a. the atomic
Neutron – means neutral
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Approx. same mass as proton, no charge.
Determines whether an element is radioactive
Determines how much an element weighs
-
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neutron + proton = atomic
mass
Forms of an element that have different numbers of neutrons are isotopes.
Electron
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Small ( ~ 1/2000 mass of proton), negative charge.
Are attracted to protons
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Move around in patterns known as orbitals.
- The orbital (or shell) is the distance from the nucleus.
-
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The oribitals have names and are limited to the number of electrons they can hold.
The electrons in the outermost orbital are known as
Nucleus
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Contains protons and neutrons
Makes up most of the mass of an atom.
Small part of atoms volume.
valance electrons.
Electron Cloud
• Space in which electrons orbit the nucleus at
high speed.
• Large part of atoms volume.
• Subdivided into Energy Levels or Shells.
• Electrons occupy the lowest energy levels.
number)
Station 2: Atomic Models
Station 3: Plum Pudding Atoms
In 1897 J.J. Thomson discovered the electron, a negatively charged particle more
than two thousand times lighter than a hydrogen atom. An atom made of
thousands of electrons would have a very high, negative electric charge. This was
not observed, as atoms are usually uncharged.
Because matter is electrically neutral, there must be a positively
charged particle that balances the negative charge on the electrons
in an atom.
If electrons are very light, these positively charged particles must
carry the mass of the atom.
Thomson therefore suggested that atoms are spheres of positive
charge in which light, negatively charged electrons are embedded,
much as raisins might be embedded in the surface of a pudding. This plum pudding
model was generally accepted. Even Thomson's student Rutherford, who would
later prove the model incorrect, believed in it at the time.
Station 4 The Rutherford Model
In 1909 Ernest Rutherford conducted what is now a famous experiment where he
bombarded gold foil with alpha particles (Helium nuclei). A source which undergoes
alpha decay is placed in a lead box with a small hole in it. Any of the alpha
particles which hit the inside of the box are simply stopped by the box. Only
those which pass through the opening are allowed to escape, and they follow a
straight line to the gold foil. The figure below shows the experiment.
Observations
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Most of the alpha particles pass straight through
Some of the alpha particles get deflected
A very few get deflected greatly.
Even fewer get bounced back
Conclusions
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The atom is 99.99% empty space.
The nucleus contains a positive charge and most of the mass
The nucleus is 100,000 times smaller than the atom.
Station 5: Rutherford Scattering simulation [PHET,
Chemistry, Rutherford Scattering].
https://phet.colorado.edu/en/simulation/rutherfordscattering
This simulation gives a microscopic picture of Rutherford’s famous experiment in
which he shot alpha particles at a thin foil of gold.
Begin with the “Plum Pudding Model”
Turn the gun on for 10 seconds and record how the alpha particles move in relation
to the atomic model:
Switch to “Rutherford Atom”
Change the number of protons to “20” at the right side of the screen. Turn the
gun on again and record your observations:
Slide the “number of protons” bar to the right little by little and observe the
“particles” as they approach the central mass. Record how the deflection of the
particles changes as one adds more protons:
Station 6: “Models of the Hydrogen Atom” simulation.
Open the “Models of the Hydrogen Atom” simulation.
http://phet.colorado.edu/new/simulations/sims.php?sim=Models_of_the
_Hydrogen_Atom
Select “Experiment” and “White Light”
Click the button on the gun to start the experiment. Describe the
movement or color changes that you see:
Switch to “Prediction” in the upper left corner of the simulation. For
each of the models, run the simulation for 10 seconds and describe the
movement/color changes you observe.
Billiard Ball
Plum Pudding
Solar System
Bohr
deBroglie
Schrödinger
Which one matches what actually happens in the “Experiment” from the
first part?