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Atomic Theory – Outline Notes
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I.
Atomic Theory is: scientific theory of structure & behavior of atoms.
II.
Atomic Theory: modified over time w/new discoveries about atoms.
A.
Around 450 BCE - Ancient Greek understandings of matter – 4 fundamental
elements
B.
1.
Fire, air, water, earth
2.
Characteristics of substances depended on ratios of these 4 things
3.
This was NOT science – no experimentation.
460 BCE to 370 BCE - Democritus - ancient Greek who coined term “atomos”
http://www.youtube.com/watch?v=NSAgLvKOPLQ (0:00 to about 3:00)
1.
“Atomos”: source of word “atom”
2.
“Atomos”: “uncuttable”, indivisible
3.
Idea of “atomos” from thought experiments - what would happen if you
kept cutting something pure in half forever?
4.
This was NOT science – no experimentation.
5.
Aristotle rejected this for the fire, air, water, earth elements so NOT
accepted until 2000+ yrs later!
C.
1803 Dalton – British teacher & scientist developed 1st modern atomic theory
using recent experiments by others– SCIENCE!
1.
Needed to explain ideas being discovered
Go to Dalton’s Playhouse: http://www.visionlearning.com/en/library/Chemistry/1/EarlyIdeas-about-Matter/49/reading (use internet explorer) Discuss each new discovery and
ask students to try to guess how the model changed because of that new
information…
2.
Joseph Priestly –
Some substances are made of two or more different substances
3.
Antoine Lavoisier’s - Law of Conservation of Mass
Mass of reactants equals mass of products
4.
Diamonds vs charcoal
Things that look very different can be made of the same stuff
5.
Dalton's theory had four main concepts:
a)
All matter is composed of indivisible particles called atoms.
b)
All atoms of a given element are identical; atoms of different
elements have different properties.
c)
Chemical reactions involve the combination of atoms, not the
destruction of atoms.
d)
When elements react to form compounds, they react in defined,
whole-number ratios.
D.
1897 JJ Thompson – Discovered the Electron (e-)
http://www.youtube.com/watch?v=Rb6MguN0Uj4
1.
Showed atoms were made of smaller parts
a)
2.
E.
Cathode Ray Tube experiment
(1)
Ray bends when 2 metal plates connected to electricity
(2)
Ray bends toward the + plate so ray is made of neg stuff
b)
Tried again w/a magnet & ray bends in predicted way
c)
Tried with different metals and all gave off cathode rays
Atom model changes
a)
e-s exist & are 1,000x smaller than H atom
b)
e-s are neg
c)
atoms usually neutral
d)
something must be +
e)
Plum Pudding (or blueberry muffin) model is result
f)
(Note: the density of the dough was thought to be light & fluffy)
1911 Ernest Rutherford – discovers nucleus
http://www.youtube.com/watch?v=dNp-vP17asI
1.
2.
3.
Gold Foil Experiment
a)
Shot tiny alpha particles at gold foil.
b)
Set up detector around foil to see where the alpha particles went
c)
MOST alpha particles went straight through…
d)
SOME particles veered to side or bounced backwards!
These results helped to show:
a)
Atoms must be mostly empty space!
b)
There must be something sm & hard inside atoms!
c)
Atoms have a sm, dense nucleus
d)
Nucleus is probably + charged
Later people also add the ideas that:
a)
Neg. electrons must be moving around quickly (so they don’t get
pulled into the positive nucleus)
b)
F.
Nucleus is made of sm particles called protons
Discoveries about electrons
http://www.youtube.com/watch?v=NSAgLvKOPLQ (5:45 to 8:15)
1.
1913 - Neils Bohr (Rutherford’s student)- Electrons in orbits
Proposed e-s arranged in concentric circular orbits around nucleus like
solar system (so also “planetary model”). 4 main ideas:
a) e-s occupy only certain stable, stationary orbits around nucleus.
b) Each orbit has an energy associated w/it. Orbit nearest nucleus has
energy of E1, the next orbit E2, etc.
c) Energy is absorbed when e-s jump from lower to higher orbits & energy
is emitted when e-s fall from higher to lower orbits.
d) The energy & frequency of light emitted or absorbed can be calculated
by using the difference btwn the 2 orbital energies.
2.
1926 – Erwin Schrödinger – Quantum Mechanical Model
Schrödinger used mathematical eqs to describe likelihood of finding an e- in
a certain position. This model does not define the exact path of an e-. It predicts
the odds of the location of the electron. Looks like a nucleus w/a e- cloud.
G.
a)
e-s whiz around like hyper flies
b)
e-s sketched out particular shapes – orbitals
c)
Orbitals are not all spherical
1932 James Chadwick – discovers neutrons
http://www.youtube.com/watch?v=_7DAlvRI1M4
1.
There were problems with the last model:
a)
How do protons stay so close together? Shouldn’t they repel?
b)
Why is mass of 2 H atoms (w/1 P) < mass of 1 He atom (w/2 P)?
Mass 4 H atoms = 1 He atom – why?
c)
Scientists could find no. of protons and mass of atoms, but they
didn’t match! Why?
2.
So Chadwick made an experiment where he shot metals with alpha
particles.
3.
a)
Something shot out of metals! (particles!)
b)
Didn’t have a charge (not e- or p+)
c)
Made protons shoot out of wax! (so particles are fast & heavy)
So, particles ~ same size & mass as protons, but w/no charge = neutrons!
----- break ----Quantum theory was a big focus during this time. (So was WWII.)It had more to do with
understanding the levels of energy inside of atoms. This was a big deal because Einstein
showed scientists that Newtonian physics was NOT complete. A lot more study was
needed to understand what happens at the atomic level. We’re not going into this this
year. You’ll get there later. Take physics!
----- break ----H.
1960’s - The Standard Model
http://t3rfde.com/wp-content/uploads/2014/02/modern_atom_model.png
1.
Many new tiny particles being discovered in particle accelerators
2.
Murray Gell-Mann & George Zweig had idea of quarks. They said mesons
& baryons made of 3 quarks or antiquarks, called up, down, or strange.
3.
e-s shot at protons in a linear accelerator & the e-s seem to bounce off
small hard cores inside the proton. James Bjorken and Richard Feynman
analyze data which later is shown to provide evidence for quarks.
4.
More evidence keeps coming from bigger particle accelerators, the latest
was the discovery of the Higgs-Boson
http://www.visionlearning.com/en/library/Chemistry/1
http://www.particleadventure.org/standard-model.html
http://www.youtube.com/results?search_query=tyler%20dewitt%20chemistry%20atom&sm=3
http://www.particleadventure.org/other/history/earlyt.html