Transcript Atomic Theory

Chapter 4
Atomic Structure
A Long, Long Time Ago…
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Greek Philosophers- 4 elements are
Earth, Water, Fire, and Air
Aristotle- first recorded atomic
thoughts
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Matter is continuous (no atoms)
Democritus (400 B.C.) - first recorded
atomic theory
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Atoms are smallest part of matter, each type
of matter has different atoms
Aristotle and Democritus
A Long Time Ago…
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Antoine Lavoisier (1782)
– Used experiments in closed containers to
develop the LCM
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Joseph Proust (1799)
– Analyzed water to develop the Law of Definite
Proportions
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John Dalton (1803)
– Compiled past research to develop the first
useful atomic theory
Lavoisier and Proust
John Dalton
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Dalton’s theory had 4
major tenets
1.
2.
3.
4.
All matter is
composed of atoms
Atoms are indivisible
Atoms of 1 element
are alike, but different
from those of other
elements
Atoms combine in
small, whole number
ratios to form
compounds
A Reminder
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Observation, Observation, Observation
Research
Hypothesis
Experiment, Revise hypothesis lots of
times
Results match….may become a theory
A Little While Ago…
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1897- J.J. Thomson
discovers the
electron using a
cathode ray tube
Cathode Ray Tube
Experiment
http://www.aip.org/history/electron/jjappara.
htm
The Nucleus Exists!
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1911- Ernest
Rutherford uses the
gold foil experiment
to “discover” the
nucleus
The Gold Foil Experiment
Results of Gold Foil
Experiment…
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http://online.cctt.org/physicslab/content/Phy1/lesso
nnotes/atomic/atomicmodelsandspectra.asp
http://micro.magnet.fsu.edu/electromag/java/ruther
ford/
Over 98% of the particles went straight
through
About 2% of the particles went through but
were deflected by large angles
About 0.01% of the particles bounced off the
gold foil
Rutherford’s Conclusion
Rutherford's Nuclear Model
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1. The atom contains a tiny dense center
called the nucleus
– the volume is about 1/10 trillionth the volume of the atom
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2. The nucleus is essentially the entire mass
of the atom
3. The nucleus is positively charged
– the amount of positive charge of the nucleus balances the
negative charge of the electrons
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4. The electrons move around in the empty
space of the atom surrounding the nucleus
Understanding Periodic
Blocks
19
K
39.0983
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Atomic Number
– # of protons
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Element Symbol
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Mass Number
– Protons + Neutrons
Can 20.0983 Neutrons
Exist???
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No, 39.0983 is an average mass of all
natural K atoms
– All K atoms MUST have 19 protons
– Some have 20 neutrons, some 19, some
21…
– Average is 20.0983 neutrons
– Individual isotopes are identified by the
number of neutrons
Identifying Protons,
Neutrons, and Electrons
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Chlorine-35 (element-mass number)
# of protons = 17
# electrons = # protons
# neutrons = mass number – protons
– 35-17 = 18
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Why no electrons in atomic mass?
– Electron has mass 1/1837 of Proton and
Neutron
Nuclear Stability
The Modern View of the
Atom
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Neils Bohr (1913) develops the planetary model of
the atom
– Developed from “electrocution” of hydrogen gas
– Only certain colors resulted
– Why???
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http://www.colorado.edu/physics/2000/qua
ntumzone/index.html
Bohr’s Hydrogen Atom
http://www.visionlearning.com/library/m
odule_viewer.php?mid=51
Schrodinger’s Revision…
http://www.colorado.edu/physics/2000/quantumzone/schroedinger.html