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HISTORY OF THE ATOMIC
MODEL
Chapters
4, 5.1,+ 25
SCIENTISTS
Aristole:
MODEL
The Greek Model (400 BC – 320 BC)
• 330 BC: Systematic concept of logic (Scientific Method)
• Atoms did not exist
• All matter was made up of 4 elements: Earth, Water, Fire, and Air
Democritus:
The Greek Model (460 BC – 370 BC)
• 400 BC: Matter can’t be divided forever; there must be
a smallest piece (atomos)
• Atoms are indestructible, indivisible, & the fundamental
units of matter
Atom: smallest particle of an element that retains the
properties of that element.
- no electric charge, electrically neutral
•No experiments to test his theories
SCIENTIST
John Dalton:
English
MODEL
Dalton’s Model
(1766 – 1844)
Dalton’s Atomic Theory (1803):
 All elements are composed of atoms that are
submicroscopic indivisible particles.



Atoms of the same elements are identical & atoms of
different elements are different.
Atoms of different elements can physically mix together or
chemically combine w/one another to form simple wholenumber ratios to form compounds.
Chemical reactions occur when atoms are separated,
rearranged or joined. Atoms of one element can never be
changed into atoms of another element.
SCIENTIST
J.J. Thomson:
English
•
•
•
•
•
MODEL
Thomson’s Model
(1856-1940)
1897: Used cathode ray tube to discover electrons
Cathode ray: glowing beam which travels from
the cathode(-) to the anode(+).
- are composed of electrons
- are attracted to positive metal plate
Atoms had negatively charged particles
ELECTRON: negatively charged subatomic particle
• not the original name (corpuscle)
“Plum Pudding” Model
•
(chocolate chip cookie) (watermelon)
• -a
ball of positive charge containing electrons
Thomson’s ATOMIC Model
POSITIVE
CHARGE
ELECTRONS
EMBEDDED
WITHIN
Cathode Ray Tube:
http://www.chem.uiuc.edu/demos/cathode.html
Robert Millikan (1868-1953)
Oil Drop Experiment (1916)
 American
 Determined
the
charge and
mass of an
electron
 The mass is
1/1840 of the
mass of a
hydrogen atom
(unit)?
SCIENTIST
Ernest Rutherford:
New Zealand
+++
+++
•
•
MODEL
Rutherford’s Model
(1871-1937)
Empty
Space
+ Nucleus
Gold Foil Experiment (1911)
Discovered that most of atom’s mass is located in the
positively charged nucleus
NUCLEUS: center of the atom composed of
PROTONS & NEUTRONS
 is 99.9% of the atom’s mass
 a marble in a football stadium
http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/ruther14.swf
Rutherford’s Gold Foil Experiment:
(1911)
http://micro.magnet.fsu.edu/electromag/java/rutherford/
Gold Foil Experiment: Rutherford
PROTON: positively charged subatomic particle
discovered by Eugen Goldstein (1850-1930)
 1886: put holes in cathode and saw rays traveling
in the opposite direction (canal rays)
NEUTRON: subatomic particle with no charge
discovered by English scientist
Sir James Chadwick (1891-1974)
 1932: mass is nearly equal to proton (1 amu)
Thomson & Rutherford proved
Dalton’s Theory incorrect:
ATOMS ARE DIVISIBLE
SCIENTIST
Niels Bohr:
(Danish)
MODEL
The Bohr Model (1885-1962)
Electrons
+++
+++



Energy
Levels
Electrons move in definite orbits around
the nucleus (planets around the sun)
1913: PLANETARY MODEL
Electrons are a part of energy levels
located certain distances from the
nucleus

Energy Levels: region around the nucleus where the
electron is likely to be moving.
 a ladder that isn’t equally spaced
 further the distance, closer the spacing
 the higher the energy level the farther it is from the
nucleus
Electrons can jump from 1 energy level to another.

Quantum Energy: amount required to move an
electron from its present energy
level to the next higher one.
SCIENTIST
MODEL
Erwin Schrodinger Quantum Mechanic Model (1887-1961)
• Austrian(1926): Wave mechanics-mathematical
• Probable location of electron
• Cloud Shaped
• Pattern similar to a Propeller blade
Louis De Broglie Quantum Mechanic Model (1892-1987)
• French (1929): Wave nature of electrons discovery
• Electrons can act like waves (Quantum Physics)
• Wave particle duality/High energy emission in
elements—Synthetic elements
Subatomic particles:
Electrons, Protons, & Neutrons
 Atomic
•
Number: Number of Protons in the
nucleus
Whole number written above chemical symbol
Ex:
Hydrogen=1(P)
Oxygen=8(P)
 Atomic
Mass #: Sum of Protons + Neutrons
Ex:
Carbon Mass #12 = 6(P) + 6(N)
Oxygen Mass #16 = 8(P) + 8(N)
A.Mass # (#P + #N) - Atomic # (#P) =
#Neutrons
LETS HAVE SOME PRACTICE
Element
Symbol
Element
Name
Mass
Number
(P+N)
Atomic
Number
(P)
Atomic
Number
(P)
6
C
Carbon
12
12
6
Mass
Number
(P+N)
C
WHAT GIVES AN ATOM ITS
IDENTITY?

Isotope: Same # of Protons,
different # of Neutrons
• Different Mass Number
• Same Atomic Number
• Chemically alike
Ex:
Carbon-12 Mass #12 = 6(P) + 6(N)
Carbon-13 Mass #13 = 6(P) + 7(N)
Atomic Mass for isotopes of Carbon = 12.01 amu
SO, WHAT GIVES AN ATOM ITS
IDENTITY?
#
of protons gives the atom its identity
#
of electrons determines the chemistry
of the atom
#
of neutrons only changes the mass of
the atom
DO NOW
There are 3 isotopes for Oxygen
O-16
O-17
O-18
1.
Write the shorthand chemical symbol for
all three isotopes
12
6 C
O-16
16
8
O
O-17
17
8
O
O-18
18
8
O
Average Atomic Mass
80% tests ---50
20% homework---100
What is your average?
(50+100)/2=75, not the case,
tests are weighted more
.80x50= 40
.20x100=20
60 is your grade
Average Atomic Mass
Two isotopes of carbon are
C-12 the abundance is 98.89%
C-13 the abundance is 1.11%
What is the average atomic mass
(12+13)/2=12.5
C-12: (98.89%/100) x 12=11.87
C-13: (1.11%/100) x 13=0.14
11.87+0.14=12.01amu
Average Atomic Mass
 Do
questions #23 & #24 on page 117
DO NOW
Determine the # of protons, neutrons, &
electrons for the 4 isotopes of zinc:
Protons
Neutrons
Electrons
64
30
Zn
30
34
30
66
30
Zn
30
36
30
67
30
Zn
30
37
30
70
30
Zn
30
40
30
DO NOW
Element X has two natural isotopes with
mass 10.012 amu and a relative
abundance of 19.91%. The isotope with
mass 11.009 amu has a relative
abundance of 80.09%.
1. Calculate the atomic mass of this element
(show all work) and then name this
element.
Nuclear Chemistry
 The
study of changes in matter that
originate in atomic nuclei
 What makes a nucleus unstable?

Too many or Too few neutrons relative to the
# of protons
 The
nuclei of unstable isotopes gain
stability by undergoing changes
Changes that Radioactive Isotopes
Undergo

Alpha α particle



Beta β particle


Release of helium nuclei
Rutherford’s Gold Foil Exp.
Release of an electron
from the breaking apart of a neutron in an atom
Gamma γ ray

Release of photons (light energy)
What can they penetrate?

Alpha α =almost nothing




Beta β = somethings



Inhalation (radon)
Open wounds
Can’t go through skin,
paper, wood, plastic,
lead, concrete
Skin & paper
Can’t go through wood, plastic, lead, concrete
Gamma γ = a lot of stuff


Skin, paper, & wood
Can’t go through lead or concrete
http://www.furryelephant.com/player.php?subject=physics&jumpTo=re/2Ms4
Half-Life
 Unstable
isotopes have
a rate of
decay, known
as half-life
Uses of Radioactive Isotopes
 Carbon
dating (pg. 806, 814,815)
 Geiger counter (pg 817)
 Film Badge (817)
 Agriculture tracers (pg 818)
 Treating Cancer (pg 819)