Transcript Unit 2 – Atomic Theory - H

Unit 2 – Atomic Theory
Chapter 4 & 11.2
Unit Test: Oct. 3, 2008
Democritus
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Lived around 400
B.C.
Came up with the
concept of the
atom
John Dalton - 1803
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Known for Billiard
Ball Model
Called the father of
Atomic Theory
Dalton’s Atomic Theory - 1803
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All matter is composed
of atoms which are
indivisible
All atoms of the same
element are identical
Atoms of different
elements are different
Atoms bond in
different proportions to
form compounds (Law
of Definite Proportions)
J. J. Thomson - 1897
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Discovered the
electron (1st
subatomic particle)
through
experiments with
cathode ray tube
Plum Pudding
model (or
Chocolate Chip
Cookie model)
Thomson’s Model
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“Pudding” or
“Cookie” is the
positive charge and
most of the mass of
the atom
“Plums” or
“Chocolate Chips”
are the scattered
electrons
POSITIVE CHARGE
ELECTRONS
Ernest Rutherford - 1910
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Nuclear Model
(atom contains a
nucleus)
Gold foil
Experiment
Rutherford’s Experiment
Rutherford’s Model
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Atoms have:

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A nucleus
Protons (positive
charge) in nucleus
Mostly open space
Electrons found
somewhere around
the nucleus
Niels Bohr - 1913
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Planetary Model
Electrons (e-) have
definite path around the
nucleus (orbit)
e- arranged around the
nucleus according to
energy level
e- with lowest energy
level are closest to
nucleus
Bohr’s Model
Quantum Mechanical Model 1923
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Electron Cloud (modern theory)
Calculates the probability of finding the
electron within a given space
Electrons, instead of traveling in
defined orbits, travel in diffuse clouds
around the nucleus
Quantum Mechanical Model
Present Model of the Hydrogen Atom
Stepwise Timeline of Atomic
Theory
Dalton
1803
Rutherford
1910
Thomson
1897
Modern Theory
Bohr
1913
Subatomic Particles
Name
Symbol
Proton
Electron
Neutron
+
H
or
p
1
e1n
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Relative
Mass
1 amu
0 amu
1 amu
Charge
Position
1
-1
0
Nucleus
Outside
Nucleus
amu – atomic mass unit; based on carbon-12
1 amu = 1/12 mass of C-12 = mass H
Impractical to use actual mass of subatomic
particles
Elements of the Periodic Table
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Atomic Number
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Identifies element
# protons
# electrons in neutral
atom
Atomic Number
Atomic Symbol
Atomic Mass
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a.k.a. mass number
# protons + # neutrons
Atomic Mass
Isotope Notation
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Element Symbol with mass number and
atomic number
Can also be the element name dash mass
number
Mass
Number
Atomic
Number
X
or
Element- Mass
Practice
Symbol
19
9
F
#
#
#
Atomic
Mass
Protons neutrons electrons Number Number
9
10
9
9
19
28
59
14
6
C
150
30
94
65
Isotopes
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Atoms of the same element with
different numbers of neutrons
Think of it as different sized shirts!
12
6
C
6 neutrons
Carbon-12
C
7 neutrons
Carbon-13
8 neutrons
Carbon-14
13
6
14
6
C
Isotopes
Average Atomic Mass
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Mass listed on the periodic table
Determined by averaging the masses
of all naturally occurring isotopes of
that element
Explains why the atomic mass is
usually not a whole number
Finding Average Atomic Mass
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You are told there are 3 isotopes of
Cycreekium and their percent
abundance:
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Cycreekium-20; 10%
Cycreekium-22; 20%
Cycreekium-23; 70%
Find their average atomic mass!
Finding Average Atomic Mass
Formula: % abundance as decimal ×
atomic mass for each isotope; sum
results for avg. atomic mass.
10% × 20amu = 0.10 × 20amu = 2.0amu
20% × 22amu = 0.20 × 22amu = 4.4amu
70% × 23amu = 0.70 × 23amu = 16.1amu
Total: 22.5amu
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Percent Abundance
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If you are given information about an
elements isotope you can estimate the
most abundant isotope!
Example: Carbon-12, Carbon-13,
Carbon-14. Look at the atomic mass
on the periodic table. Which isotope is
the mass closest to?
End of Unit 2 Notes!
Study for Unit 2 Test on:
October 3, 2008