Unit 3 - Atomic Theory
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Transcript of Unit 3 - Atomic Theory
8/3/2019 Unit 3 - Atomic Theory
http://slidepdf.com/reader/full/unit-3-atomic-theory 1/24
The Atomic TheoryUnit 3 – Honors Chemistry
By PresenterMedia.com
8/3/2019 Unit 3 - Atomic Theory
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• Democritus (~400 BC)• Greek philosopher • Thought that all matter
was made of smallparticles.
• Called them “ATOMS”
which were indivisibleand indestructible.
Discovering the Atoms
8/3/2019 Unit 3 - Atomic Theory
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• Antoine Lavoisier (1789)• Law of Conservation of Mass• Mass can neither be created
nor destroyed!• Joseph Proust (1797)
• Law of Definite Proportions• Compounds always contain
the same proportion of
elements by mass.
Discovering the Atoms
8/3/2019 Unit 3 - Atomic Theory
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• John Dalton (1803)• English Scientist who created
the first Atomic Theory:1. All matter is made of atoms.2.
Atoms of an element areidentical in size and mass.3. Atoms of different elements
can mix physically or combine chemically.
4. In reactions, atomscombine, separate or rearrange.
5. Atoms cannot be divided,created or destroyed.
Discovering the Atom
John Dalton’s
Atom
8/3/2019 Unit 3 - Atomic Theory
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• JJ Thomson (1897)• Performed the cathode
ray experiments• Discovered electrons• Said electrons areembedded throughoutthe atom.
• Plum Pudding Model•
The atoms containedpositively-chargedmaterial, withnegatively-chargedelectrons in it.
Discovering the Atom
8/3/2019 Unit 3 - Atomic Theory
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• R.A. Millikan (1909)• The Oil Drop Experiment• Calculated the specific
mass and charge of theelectron.
• Mass = 9.109 x 10 -28 kg
Discovering the Atom
8/3/2019 Unit 3 - Atomic Theory
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• Ernest Rutherford (1911)• The Gold Foil Experiment
• Fired alpha rays (+) ata sheet of gold foil.
• Most of the rays passedthrough, but somebounced back!
• Conclusions•
The atom is mostlyempty space• A dense, positively-charged nucleus is incenter of each atom
Discovering the Atom
8/3/2019 Unit 3 - Atomic Theory
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• Eugene Goldstein (1886)• Observed a Carthode Ray
Tube• Some particles travelled to
the negative end.• Discovered the proton!
• 1840 times bigger thanan electron.
Discovering the Atom
8/3/2019 Unit 3 - Atomic Theory
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• Neils Bohr (1922)• Planetary Model of the
Atom• Electrons move indefinite orbits aroundthe nucleus
• Each energy level islocated at a certaindistance from thenucleus
Discovering the Atom
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• James Chadwick (1932)• Discovered the neutron.• No Charge•
Same mass as the proton.
Discovering the Atom
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• Enrico Fermi (1942)• Successfully split the
atomic nucleus• Paved the way for nuclear
power and weapons.
Discovering the Atom
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• EVERYTHING is made ofATOMS!
• Understanding the atomhelps us understand howeverything works.
• Understanding thestructure of the atom helpsus understand how it doeswhat it does.
Atomic Structure
8/3/2019 Unit 3 - Atomic Theory
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• The Atom is mostlyempty space.
• A tiny, positively chargednucleus in the center.
• Even tinier, negativelycharged electronswhirling around it.
• Atomic Structure
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• The Nucleus• Makes up 99.99% of the
atom’s mass. • About 1 fm wide (10 -15 )• Composed of Protons
and Neutrons.
• Atomic Structure
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• Protons (p +)• Positively-Charged
Particle• 1 amu (10 -27 kg)• Determines the type of
element.• Neutrons (n 0)
• Carries NO CHARGE!• 1 amu (10 -27 kg)• Holds the nucleus
together with strongforces.
• Atomic Structure
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• Electron Clouds• Shows the probable
location of an electron.• Lowest energy level is
closest to the nucleus.• Electrons (e -)
• Negatively-ChargedParticle
•
0 amu (10 -31 kg)• Determines the chemical
properties of the element.
Atomic Structure
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• Atomic Number (Z)• The Number of Protons in
an Element• Every element has a
different Atomic Number!• In a neutral atom, the
number of protons equalsthe number of electrons.
•
Mass Number (A)• The number of Protons +
the number of Neutrons
Identifying Elements
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Identifying Elements
Z = #p + = #e -
A = Z + n0
n 0 = A - Z
8/3/2019 Unit 3 - Atomic Theory
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• Elements• Different numbers of protons.
• Ions•
Different numbers ofelectrons.• Lose an e- Positive Ion• Gain an e- Negative Ion
• Isotopes• Different numbers of neutrons.• Hydrogen has Three Isotopes• Unstable isotopes are
radioactive!
Changing Elements
8/3/2019 Unit 3 - Atomic Theory
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• Accounts for theabundance of eachisotope.
•
The number found on theperiodic table.
Average Atomic Mass
Atomic Mass = (0.7890)(24 amu) + (0.1000)(25 amu) + (0.1110)(26 amu)