chapter 5 - atomic theory and structure (for entry)
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Atomic Theory and Structure
Engr. Yvonne Ligaya F. Musico
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Learning Objectives1. Discuss the historical concept of atoms
2. State the premises of Daltons AtomicTheory
3. Identify the three most importantparticles of an atom.
4. Differentiate proton, neutron andelectron
5. Determine the atomic number and
mass number of an atom6. Calculate the isotopic mass and
isotopic abundances of different atoms
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TOPIC Evolution of the Different Atomic
Theories
Structure of Atom and Propertiesof Atom
First Slide Last Slide
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Evolution of Different AtomicTheories
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The History of the Discovery of the Atom
The Greek Model of the Atom
Daltons Atomic Theory
Thomson Model
Rutherford Model
Bohr Model Modern Atomic Theory
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The Greek Model of the Atom
Beginning with Democritus, wholived during the late 5th and early
4th centuries BC, Greekphilosophers developed a theoryof matter that was not based onexperimental evidence, but ontheir attempts to understand theuniverse in philosophical terms.
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The Greek Model of the Atom
According to this theory, all
matter was composed of tiny,indivisible particles called
atoms (from the Greek word
atomos, meaningindivisible).
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The Greek Model of the Atom
According to the ancient Greeks,
atoms were all made of the same
basic material, but atoms of
different elements had different
sizes and shapes
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The Greek Model of the Atom
The sizes, shapes, and
arrangements of a materials
atoms determined the materials
properties.
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Daltons Atomic TheoryLate 1700s - John Dalton-
England
Teacher- summarized results ofhis experiments and those ofothers.
Daltons Atomic Theory
Combined ideas of elements withthat of atoms.
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Daltons Atomic Theory
All matter is made of tiny
indivisible particles called
atoms.
Atoms of the same element are
identical, those of different
atoms are different.
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Daltons Atomic Theory
Atoms of different elementscombine in whole number
ratios to form compounds.
Chemical reactions involve the
rearrangement of atoms. Nonew atoms are created ordestroyed.
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Just How Small an Atom
Think of cutting a piece of lead intosmaller and smaller pieces
How far can it be cut?
An atom is the smallest particle of anelement that retains the properties ofthat element
Atoms-very small
still observable with properinstruments
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Thomson Model
J. J. Thomson - English
physicist. 1897
Made a piece of equipment
called a cathode ray tube.
It is a vacuum tube - all theair has been pumped out.
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J.Js Atomic Model
Plum Pudding model
-electrons distributed randomly in a diffuse positive
cloud.
-plum pudding model: raisins dispersed in
pudding.
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Thomsons Experiment
Voltage source
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Vacuum tube
Metal Disks
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Thomsons Experiment
Voltage source
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Thomsons Experiment
Voltage source
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Thomsons Experiment
Voltage source
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Thomsons Experiment
Voltage source
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Passing an electric current makes a
beam appear to move from the
negative to the positive end
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Thomsons Experiment
Voltage source
+-
Passing an electric current makes a
beam appear to move from the negative
to the positive end
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Thomsons Experiment
Voltage source
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Passing an electric current makes a
beam appear to move from the negative
to the positive end
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Thomsons Experiment
Voltage source
By adding an electric field
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Thomsons Experiment
Voltage source
By adding an electric field
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Thomsons Experiment
Voltage source
By adding an electric field
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Thomsons Experiment
Voltage source
By adding an electric field
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Thomsons Experiment
Voltage source
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Thomsons Experiment
Voltage source
By adding an electric field
+
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Thomsons Experiment
Voltage source
By adding an electric field
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Thomsons Experiment
Voltage source
By adding an electric field he found that the
moving pieces were negative (electron)
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Other Particles
Proton - positively charged
pieces 1840 times heavier
than the electronby E.Goldstein
Neutron - no charge but the
same mass as a protonbyJ. Chadwick
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Rutherford Model
Ernest Rutherford -English
physicist. (1910)
Believed in the plum puddingmodel of the atom
Wanted to see how big they are.
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Rutherfords Experiment
Used radioactivity.
Alpha particles - positively charged
pieces- helium atoms minus
electrons
Shot them at gold foil which can be
made a few atoms thick.
When an alpha particle hits afluorescent screen, it glows.
Heres what it looked like
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Rutherfords Experiment
Lead
blockUranium
Gold Foil
Fluorescent
Screen
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Rutherfords Experiment
What he expected??
The alpha particles to pass
through without changing
direction very much.
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Rutherfords Experiment
What he expected..
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Rutherfords Experiment
Because
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He thought the mass was evenly
distributed in the atom
Rutherfords Experiment
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Rutherfords Experiment
Since he thought the
mass was evenly
distributed in the atom
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Rutherfords Experiment
What he got
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Rutherfords Experiment
How he explained it!
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Atom is mostly empty.
Small dense,
positive piece
at center.
Alpha particles
are deflected by
it if they get close
enough.
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Rutherfords Experiment
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Rutherfords Experiment
Since most of the particles went
through, it was mostly empty space.
Because the pieces turned so much,the positive pieces were heavy.
Small volume, big mass, big density.
This small dense positive area is the
nucleus.
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Bohr Model
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Bohr Model
Line-Emission Spectrum
ground state
excited state
ENERGY IN PHOTON OUT
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Bohr Model
e- exist only in orbits with
specific amounts of energy called
energy levels
Therefore
e-
can only gain or lose certainamounts of energy
only certain photons are produced
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Bohrs Model
1
23
45
6 Energy of photon
depends on thedifference in energylevels
Bohrs calculated
energies matchedthe IR, visible, andUV lines for the Hatom
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Other Elements
Each element has a unique bright-lineemission spectrum.
Atomic Fingerprint
Helium
Bohrs calculations only worked for
hydrogen!
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Subatomic Particles
Quarks
component
of protons& neutrons
6 types
3 quarks =
1 proton or
1 neutron
He
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Neutrons and protons are made up of
up quarks and down quarkstwo of
the six different kinds of quarks.
Quarks are unique among all
elementary particles in that they have
electric charges that are fractions of
the fundamental charge.
Quarks
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Quarks
All other particles have electric
charges of zero or of whole multiples
of the fundamental charge. Up
quarks have electric charges of +2/3.
Down quarks have charges of -1/3.
A proton is made up of two up quarks
and a down quark, so its electriccharge is 2/3 + 2/31/3, for a total
charge of +1.
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Quarks
A neutron is made up of an up quark
and two down quarks, so its electric
charge is 2/31/31/3, for a net
charge of zero.
Physicists believe that quarks are
true fundamental particles, so they
have no internal structure andcannot be split into something
smaller.
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Quarks
Physicists believe that quarks are
true fundamental particles, so they
have no internal structure and
cannot be split into something
smaller.
Microsoft Encarta Reference Library 2003. 1993-2002 Microsoft Corporation. All
rights reserved.
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Summary of the Model of the
Evolution of Atom
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Structure and Properties of
Atoms
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Structure and Properties of
Atoms
Properties of subatomic particles
Structure of atoms
Counting the pieces
Isotopes
LAST SLIDE
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Structure of Atoms
Electrons Negatively charge
Moving around the nucleus
Nucleus Protonspositively charge
Neutronsneutral
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Properties of Subatomic
Particles
Name Symbol Charge Relative
mass
Actual
mass (g)
Electron e- -1 1/1840 9.11 x 10-28
Proton p+ +1 1 1.67 x 10-24
Neutron n0 0 1 1.67 x 10-24
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Counting the Pieces
Atomic Number number of protons in the nucleus
number of protons determines kindof atom (since all protons are alike!)
the same as the number ofelectrons in the neutral atom.
Mass Number the number of protons + neutrons.
These account for most of mass
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Atomic Symbols
Show themass number and atomic number
Give the symbol of the element
mass number23 Na sodium-23
atomic number 11
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Atomic Number on the Periodic
Table
11
Na
Atomic Number
Symbol
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All atoms of an element have
the same number of protons
11
Na
11 protons
Sodium
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Subatomic Particles in Some
Atoms
16 31 65O P Zn
8 15 308 p+ 15 p+ 30 p+
8 n 16 n 35 n
8 e
-
15
e
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30 e
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Learning Check?
YES NO
SKIP
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Solution
State the number of protons for atoms of
each of the following:
A. Nitrogen
2) 7 protons
B. Sulfur
2) 16 protons
C. Barium3) 56 protons
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Isotopes
Atoms with the same number of protons, but
different numbers of neutrons.
Atoms of the same element (same atomic number)
with different mass numbers
Isotopes of chlorine
35Cl 37Cl17 17
chlorine - 35 chlorine - 37
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Isotopes
Addison-Wesley Publishing Company, Inc.
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Isotopes of Hydrogen
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Relative Atomic Mass
12C atom = 1.992 10-23 g
atomic mass unit (amu)
1 amu = 1/12 the mass of a12C
atom
1 p = 1.007276 amu1 n = 1.008665 amu
1 e- = 0.0005486 amu
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Average Atomic Mass
weighted average of all isotopes
on the Periodic Table
round to 2 decimal places
100
(%)(mass(mass)(%) )
Avg.
AtomicMass
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Learning Check
Calculate the avg. atomic mass of
oxygen if its abundance in
nature is 99.76% 16O, 0.04%17O, and 0.20% 18O.
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Solution
Avg.AtomicMass
100(18)(0.20)(17)(0.04))(16)(99.76 16.00
amu
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Learning Check
Find chlorines average atomicmass if approximately 8 of every
10 atoms are chlorine-35 and 2are chlorine-37.
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Solution
Avg.AtomicMass
100
(37)(20)(35)(80)35.40 amu
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Learning Check
Gallium is a metallic element found in
small lasers used in compact disc players.
In a sample of gallium, there is 60.2% ofgallium-69 (68.9 amu) atoms and 39.8% of
gallium-71 (70.9 amu) atoms. What is the
atomic mass of gallium?
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Atomic Mass
Listed on the periodic table
Gives the mass of average atom of each element
compared to 12C
Average atom based on all the isotopes and their
abundance %
Atomic mass is not a whole number
Atomic mass is the weighted average mass of all
the atomic masses of the isotopes of that atom.
Na
22.99
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Solution
Using the periodic table, specify the
atomic mass of each element (round to the
tenths place):
A. calcium _40.1 amu _
B. aluminum _27.0 amu _
C. lead _207.2 amu_
D. barium _137.3 amu_
E. iron _55.8 amu__
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Finding an Isotopic MassAssign X and Y values:
X = % 10B Y = % 11B
Determine Y in terms of X
X + Y = 100
Y = 100 - X
Solve for X:
X (10.0) + (100 - X )(11.0) = 10.8
100 100
Multiply through by 10010.0 X + 1100 - 11.0X = 1080
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Finding an Isotopic Mass
Collect X terms
10.0 X - 11.0 X = 1080 - 1100
- 1.0 X = -20
X = -20 = 20 % 10B
- 1.0
Y = 100 - X
% 11B = 100 - 20% = 80% 11B
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Learning Check
Copper has two isotopes 63Cu (62.9 amu)
and 65Cu (64.9 amu). What is the %
abundance of each isotope? (Hint: Check
periodic table for atomic mass)
1) 30% 2) 70% 3) 100%
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Solution
2) 70%
Solution
62.9X + 6490 = 64.9X = 6350
-2.0 X = -140
X = 70%
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Thanks for listening
Stand by for the next topic