Download Early Atomic Theorists

Early Atomic Theorists
John Dalton (1766-1844)
Democritus (460-370 BC)
No
Research
All matter is
composed of
atoms that are
indestructible
and indivisible
Research
Dalton’s Atomic Theory
All elements are composed of tiny indivisible particles
called atoms.
Atoms of the same element are identical. Atoms of any
one element are different from those of any other
element.
Atoms cannot be created, divided into smaller particles
or destroyed.
Atoms of different elements can physically mix together
or can chemically combine with one another in simple
whole-number ratios to form compounds.
Chemical reactions occur when atoms are separated,
joined, or rearranged. Atoms of one element, however,
are never changed into atoms of another element as a
result of a chemical reaction.
The Atom
The smallest particle of an element that retains
the property of that element
Relative Size
World Population
6000000000
Atoms in a penny 29000000000000000000000
Discovering the Electron
Cathode (-)
Anode (+)
Experiments with electricity, using cathode ray
tubes led to the discovery cathode rays.
oCathode rays were a stream of charged particles
oThe particles carried a negative charge
JJ Thompson
Determined the
Charge to Mass ratio
of cathode particles
(~1/1840 the mass of
a hydrogen atom)
and discovered the
electron
Disproved Daltons theory that atoms were
indivisible because he determined that the
mass of a cathode particle was far less than
that of a hydrogen atom.
+
-
+ -
Proposed the “Plum Pudding”
model of the atom
+
-
+
-
+
+
-
+
-
Ernest Rutherford
Discovered
the nucleus
of the atom
with the
“Gold Foil”
experiment
Nuclear Model of the Atom
o Most of the atom consist of electrons
moving rapidly through empty space.
o Electrons are held in place in the atom by
their attraction to a positively charged
nucleus
Does this picture
accurately represent
Rutherford’s Nuclear
Model?
James Chadwick
Discovered
the Neutron
Rutherford model, consisting of electrons
and protons could not account for the total
mass of the atom, which led to the discovery
of the neutron.
Properties of Subatomic Particles
Particle Symbol
Electron
Proton
Neutron
ep+
n0
Location
Space surrounding
the nucleus
Nucleus
Nucleus
Relative
Electrical
Charge
Relative
Mass
Actual
Mass (g)
1-
1_
1840
9.11 x 10-28
1+
1
1.637 x 10-24
0
1
1.675 x 10-24
Review
6
Atomic = # protons
Number = # electrons
C
12.011
Atomic
Number
=
Mass Number = protons + neutrons
The weighted average mass of all the
isotopes of an element
Change in the number of protons results in a new atom
Change in the number of electrons results in an ion (+ or – charge)
Change in the number of neutrons results in an isotope
Isotopes
Atoms of the same element that contain the same
number of protons and different numbers of neutrons.
Nuclear or Nuclide notation
Isotope Notation
(used in nuclear equations)
C-14
Mass
Number
Atomic
Mass
14
6
C
Mass
Number
Atomic Mass Problems
Boron has two naturally occurring isotopes: boron-10 (19.8%, 10.013 amu)
and boron 11 (80.2%, 11.009 amu). What is the atomic mass of boron?
Find the Abundance x Mass for each isotope and then add products together.
0.198 x 10.013 = 1.98
0.802 x 11.009 = 8.83
1.000
10.81 amu
Unstable Nuclei and Radioactive Decay
o Nuclear Reactions involve a change in the nucleus of an
atom
C   N
14
6
0
1
14
7
o Some substances spontaneously emit radiation in a
process called radioactivity due to nuclear instability
(stability is determined by neutron to proton ratios)
o Rays and particles emitted by radioactive materials are
called radiation
o Unstable nuclei decay until they form stable nonradioactive nuclei
Types of Radiation
Alpha
226
88
Ra  He  Rn
4
2
Beta
<
222
86
<
C   N
14
6
0
1
14
7
Gamma
U  Th He  
238
92
234
90
4
2
0
0
Pre-class Activity 11/11/08
What type of nuclear decay has neptunium-237
undergone in the following reaction?
237
93
Np233
91 Pa  ___
Alpha, a, or 4 He
2
Pre-Class Activity 11/12/08
Which subatomic particles are involved in
chemical reactions?
Electrons
Which subatomic particles are involved in
nuclear reaction?
Protons, Neutrons and Electrons
Characteristics of Chemical and Nuclear
Reactions
Chemical Reactions
Nuclear Reactions
Occur when bonds are broken and Occur when nuclei emit particles
formed
and/or rays
Atoms remain unchanged,
although they may be rearranged
Atoms are converted into atoms of
another element
Only Valence (outermost)
electrons are involved
May involve protons, neutrons,
and electrons.
Associated with small energy
changes
Associated with large energy
changes
Reaction rates are influenced by
temperature, pressure,
concentration, and catalysts.
Reaction rates are not influenced
by temperature, pressure,
concentration, and catalysts.
Relative Strength and Mass of
Radioactive Particles
6.64 x 10-24
9.11 x 10-28
0
Increasing Mass
Alpha
Beta
Gamma
Increasing Strength
(Blocked By)
Paper
Metal Foil
Not completely
blocked by lead
or cement
Nuclear Stability
(Electrostatic Force vs. Nuclear Force)
Electrostatic force arises from the
interaction between two protons (repulsive
force)
Nuclear force arises between protons and
neutrons due to their close proximity to
one another
Neutron to Proton Ration and the Band of
Stability
1.5:1
1:1
As the atomic number
increases, more and more
neutrons are needed to
create a strong nuclear
force to oppose and
increasing electrostatic
force
Radioactive Decay and Stability
C
1.5:1
A
1:1
B
Alpha Decay Reduces
the number of
neutrons and the
number of protons in
the nucleus.
Alpha Decay often
occurs in elements
with an atomic number
of 83 or higher.
In what region of the
graph would this type of
decay be most
C
effective?
Radioactive Decay and Stability
1.5:1
A
1:1
Beta Decay occurs
in atoms that has
too many neutrons
relative to its
number of protons
B
1
0
n p  
1
1
0
1
In what region of the
graph would this type of
decay be most
effective?
A
Radioactive Decay and Stability
1.5:1
1:1
A
Positron emission
occurs in atoms
where the number
of protons is high
relative to its
number of neutrons
B
1
1
p  01n  10
In what region of the
graph would this type
of decay be most
effective?
B
Radioactive Decay and Stability
1.5:1
1:1
A
Electron Capture
occurs in atoms
where the number
of protons is high
relative to its
number of neutrons
B
1
1
p  10e 01n
In what region of the
graph would this type
of decay be most
effective?
B
Writing Nuclear Equations
http://www.sciencegeek.net/Chemistry/tat
ers/Unit1NuclearEquations.htm
Band of Stability Practice Questions
http://www.algebralab.com/practice/practic
e.aspx?file=Reading_TheBandOfStability.
xml
Pre-Class Activity 11/17/08
Complete the following nuclear equation, state the
type of decay and explain why this nuclide decays
in this way.
0
142
142
e
1
61
60
Pm  __ Nd
Electron Capture, the neutron to proton ration of Pm-142
falls below the band of stability
Chapter 25 Homework Quiz Thursday
Chapter 25 Test Monday
Transmutation
Conversion of an
element into an
atom of another
element
All nuclear reactions are:
transmutation reactions
o Some transmutation reactions are induced
o All transuranium elements
(atomic #93 and greater) have
been produced through induced
transmutation.
Writing Induced Transmutation Reactions
Write the balanced nuclear equation for the induced
transmutation of aluminum-27 into sodium-24 by
neutron bombardment. An alpha particle is released in
the reaction.
27
13
Al  n Na He
1
0
24
11
4
2
Write the balanced nuclear equation for the alpha
particle bombardment of Pu-239. One of the reaction
products is a neutron.
239
94
Pu  He  Cm n
4
2
242
96
1
0
Radioactive Decay
 Radioactive decay rates are measured in
half-lives (amount of time it takes for half of a
sample of radioactive nuclei to decay)
Equation
final  1 
 
initial  2 
Possible Variables
n
Initial amount of isotope
Final amount of isotope
Time elapsed
Number of half-lives
Pre-Class Activity 11/19/08
A sample of radioactive iridium has a half life of 12 years.
In 60 years, how much iridium would remain from a 50g
n
sample?
Final
1
 
 
Initial  2 
Initial= 50g
Final  1 
 
50
2
Final= ?
Time Elapsed=
60 years
# of half lives= 60/12 = 5
Value of 1 half life= 12 years
n
Final  1 
 
50
2
32 x  50
5
Final 1

50
32
x  50 / 32  1.6 g
Nuclear Reactions and Energy
Nuclear Fission
Atoms with a mass number greater than 60
tend to undergo nuclear fission in which an
atom “splits” apart.
Nuclear Fusion
Atoms with a mass number less than 60 tend to
undergo nuclear fusion in which two lighter
atoms fuse together.
Binding Energy
The amount of energy required to break
one mole of nuclei into individual nucleons