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The Structure of Atoms
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Bonds Atoms want a full valence shell.
They can share or take electrons from anotheratom to fill.
They will do whatever is easiest - gain a
few to fill it
Orlose a few to drop down to their
already filled shell.
Carbon wants 4 electrons
so will form 4 bonds
both atoms gain electrons by
sharing to = full valence shell
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What about the Nucleus?
Positive Charge
Mass = 1
Elements are defined by thenumber ofprotons in the
nucleus
Protons:
Neutrons:
No Charge (are neutral)Mass = 1
Elements can have atoms with differing # of neutrons.
Atoms of the same element but w/ different # of neutrons
= I s o t o p e s
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Elementary particles What are Protons and Neutrons made up of?
Quarks!
What are Quarks made of?
They appear to be the fundamental particle --They are not made up of anything else.
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Quarks carry partial charges
Quark Chargeup + 2/3
down - 1/3
top + 2/3
bottom -1/3
charm +2/3
strange -1/3
Electrons have -1 Photons have 0 charge
Other elementary
particles you know:
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Add it up:
Neutron:
1 up quark +
2 down quarks
1x(+2/3)
2x(-1/3)
2x(+2/3)1x(-1/3)
+3/3
Proton:
2 up quarks +1 down quark
0/3
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What holds it all together?
Strong Force uses Gluons to hold quarks
together into protons and neutrons.
Nucleus held together by the Strong Forcetoo.
Very very strong, but acts only across very
very smalldistances such as the width of a
nucleus.
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Forces Interact via
force carrier particles Remember the basketball example.
Electromagneticforces carrier particle =
It interacts with chargedparticles
Strong forces carrier particle =
Gravitys force carrier particle =
Photon
Electrons & Protons
Gluon
Graviton
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Quick Quiz:
Which of the following are fundamental particles?
Electrons
Protons Neutrons
Quarks
Photons
Nuclei Atoms
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Standard Model of MatterComposed of atoms which are constructed of:
Quarks combined into protons & neutrons.
Quarks held together by strong force/gluons. Protons & Neutrons all held together to make a
Nucleus by strong force/gluons.
Electrons(a type of lepton a fundamental particle)
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CERN
Large Particle Collider
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Some nuclei are unstable
Strong force not quite strong enough in
large molecules.
These nuclei spontaneously spit outparticles from the nucleus.
Radioactivity!
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Types of Radioactivity
Alpha decay
Beta decay
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Alpha decay
Releases an alpha particle
2 protons & 2 neutrons
Whats in the nucleus now?
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Beta decay
A neutron kicks out a tiny,
negatively charged particle.
Whats in the nucleus now?
a beta particle
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Rate of Decay Half-life
For a SAMPLE of atoms, rate is constant.
Measure rate in half-life
Time it takes for half the sample to decay.
When a given atom decays is unpredictable .
So decay rate is the probability of decay over time.
What is wrong with this definition?
Half-life equals half the time it takes for the sample to decay
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Application: Radiometric Dating
See in-class worksheet