Week of Monday November 13 th , 2006
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Transcript of Week of Monday November 13 th , 2006
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Week of Monday November 13th, 2006
The atom
Rutherford’s Problem
Niels Bohr’s Solution
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Monday November 13th, 2006
The atomRutherford’s Problem
Niels Bohr’s Atomic ModelBohr’s Problem
Heisenberg’s Uncertainty Principle
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Drill
• Why don’t the nuclei of the atoms in your bottom touch the nuclei of atoms in the chair when you sit down?
• Atomic # number means the # of ______ and when the atom is neutral, the atomic # will be the same as the # of _________.
• Convert units:– 500 mL to ____________pL 13L = 13,000 ____– 17 ms to ____________Ms 0.1m = 100
_____– 3,001 mm to _______m 0.1 cm = 1 _____
500,000,000,0005 x 1011
0.000 000 0171.7 x 10-8
3.001
mL
mmmm
protons
electrons
Electrons repel each other.
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Subatomic particles
• Protons
• Neutrons
• ElectronsAll mass is in the nucleus
Mass = 1/2000th of The mass of neutronsOr protons.
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The world of the electron
• Electrons move about the nucleus (protons & neutrons)
• Electrons are exceedingly tiny– Rules are different for them– They live in the world of quantum mechanics
• The line separating matter from energy blurs
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Rutherford’s problem
Rutherford thought:• Nucleus is positive
(protons & neutrons)
• Electrons are negative
• Electrons orbit around nucleus like planets around the sun
Questions that remain:1. How do electrons manage
to stay apart from nucleus (opposites attract)?
2. When you add energy to atoms, why do they give off light?
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Niels Bohr’s Solution
1. Electrons can stay separate from nucleus if:
• Electrons have their own energy that keeps them from getting sucked into nucleus
Bohr tries to prove this by:• Predicting how much energy
that is for each electron– Kinetic energy of each
electron = KE = ½mv2
• Finding how far away those orbits are from nucleusThey should orbit at very
specific distances away from the nucleus for model to be stable
1885 - 1962
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Bohr’s model of the atom
nucleus
Electron orbitals/energy levels
Electron loses energy as it falls down an energy levelhv is wavelength of light given off
Lower energy Levels are closer to nucleus.
Higher energy Levels are farther from nucleus.
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Niels Bohr’s Solution
2. Atoms give off light when they absorb energy because:
• Each orbital = an energy level
• Electrons can jump energy levels when energy is added to an atom
• Electrons give off energy (light) when source of energy is taken away
• Light wavelength depends on how far electrons fall
1885 - 1962
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Bohr’s problem
• Could not measure how fast electrons moved without losing their location.
• Could not pinpoint electron location without losing information on their velocity.
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Schrödinger’s theory
• Thinks Bohr is wrong:– Electrons aren’t really matter, but waves of
energy
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Heisenberg’s Uncertainty Principle
Quantum mechanics– Impossible to know both location &
velocity of electron because observation involves using light.
• Light will change location and velocity of electron because it adds energy!
– What you can know is the probability of electron’s location & velocity
– Electron orbital now area where electron has a probability of being found
– Answers the particle/wave argument
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Atom in its neutral state
• # protons
• This is the way elements are shown in the PT
= atomic # = # electrons
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Normal (on earth) chemical rxns
Atoms Δ # of electrons by– Stealing– Losing– Sharing
with other atoms
Δ means “change”
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Nuclear Chemistry
• If you Δ what is in the nucleus you are doing nuclear chemistry– Δ # protons you have a new element– Δ # neutrons radioactive decay
Δ means “change”
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Where do elements come from?
While you are watching movie, write down no more than 4 words for each question.
HW for tonight
Rewrite your answers in complete sentences.
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Niels Bohr