1. Early Atomic Theorists
John Dalton ( )
Democritus ( BC)
All matter is composed of atoms that are indestructible and indivisible
No Research
Research

2. 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.

3. The Atom
The smallest particle of an element that retains the property of that element
Relative Size
World Population
Atoms in a penny

4. Discovering the Electron
Cathode (-)
Anode (+)
Experiments with electricity, using cathode ray tubes led to the discovery cathode rays.
Cathode rays were a stream of charged particles
The particles carried a negative charge

5. JJ Thompson Proposed the “Plum Pudding” model of the atom
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 - - - -

6. Ernest Rutherford
Discovered the nucleus of the atom with the “Gold Foil” experiment

7. Nuclear Model of the Atom
Most of the atom consist of electrons moving rapidly through empty space.
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?

8. 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.

9. Properties of Subatomic Particles
Symbol
Location
Relative
Electrical
Charge
Relative Mass
Actual
Mass (g)
Electron e-
Space surrounding the nucleus 1- 1_
1840
9.11 x 10-28
Proton p+
Nucleus 1+ 1
1.637 x 10-24
Neutron n0
1.675 x 10-24

10. Review C = Mass Number 6 = # protons Atomic Number = # electrons
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

11. Isotopes C-14 Nuclear or Nuclide notation Isotope Notation
Atoms of the same element that contain the same
number of protons and different numbers of neutrons.
Nuclear or Nuclide notation
(used in nuclear equations)
Isotope Notation
C-14
Mass Number
Mass Number
Atomic Mass

12. Atomic Mass Problems
Boron has two naturally occurring isotopes: boron-10 (19.8%, amu) and boron 11 (80.2%, amu). What is the atomic mass of boron?
Find the Abundance x Mass for each isotope and then add products together.
0.198 x = 1.98
0.802 x = 8.83
amu

13. Unstable Nuclei and Radioactive Decay
Nuclear Reactions involve a change in the nucleus of an atom
Some substances spontaneously emit radiation in a process called radioactivity due to nuclear instability (stability is determined by neutron to proton ratios)
Rays and particles emitted by radioactive materials are called radiation
Unstable nuclei decay until they form stable non-radioactive nuclei

14. Types of Radiation
Alpha
Beta
Gamma
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15. Pre-class Activity 11/11/08
What type of nuclear decay has neptunium-237 undergone in the following reaction?
Alpha, a, or

16. Pre-Class Activity 11/12/08
Which subatomic particles are involved in chemical reactions?
Which subatomic particles are involved in nuclear reaction?
Electrons
Protons, Neutrons and Electrons

17. Characteristics of Chemical and Nuclear Reactions
Chemical Reactions
Nuclear Reactions
Occur when bonds are broken and formed
Occur when nuclei emit particles 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.

18. Relative Strength and Mass of Radioactive Particles
6.64 x 10-24
9.11 x 10-28
Increasing Mass
Alpha
Beta
Gamma
Increasing Strength
(Blocked By)
Not completely blocked by lead or cement
Paper
Metal Foil

19. 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

20. Neutron to Proton Ration and the Band of Stability
1:1
1.5:1
As the atomic number
increases, more and more
neutrons are needed to
create a strong nuclear
force to oppose and
increasing electrostatic
force

21. Radioactive Decay and Stability
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.
1.5:1 A
1:1 B
In what region of the graph would this type of decay be most effective? C

22. Radioactive Decay and Stability
1:1
1.5:1
Beta Decay occurs in atoms that has too many neutrons relative to its number of protons A B
In what region of the graph would this type of decay be most effective? A

23. Radioactive Decay and Stability
1:1
1.5:1
Positron emission occurs in atoms where the number of protons is high relative to its number of neutrons A B
In what region of the graph would this type of decay be most effective? B

24. Radioactive Decay and Stability
1:1
1.5:1
Electron Capture occurs in atoms where the number of protons is high relative to its number of neutrons A B
In what region of the graph would this type of decay be most effective? B

25. Writing Nuclear Equations
Band of Stability Practice Questions

26. Pre-Class Activity
Complete the following nuclear equation, state the type of decay and explain why this nuclide decays in this way.
Electron Capture, the neutron to proton ration of Pm-142 falls below the band of stability
Chapter 25 Homework Quiz – Friday 11/20
Chapter 25 Test – Tuesday 11/24

27. Transmutation All nuclear reactions are: transmutation reactions
Conversion of an
element into an
atom of another
element
All nuclear reactions are:
transmutation reactions
Some transmutation reactions are induced
All transuranium elements
(atomic #93 and greater) have
been produced through induced
transmutation.

28. 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.
Write the balanced nuclear equation for the alpha particle bombardment of Pu One of the reaction products is a neutron.

29. 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
Possible Variables
Initial amount of isotope
Final amount of isotope
Time elapsed
Number of half-lives
Half-life

30. Sample Problem
A sample of radioactive iridium has a half life of 12 years. In 60 years, how much iridium would remain from a 50g sample?
Initial=
Final=
Time Elapsed=
# of half lives=
Value of 1 half life=
50g ?
60 years
60/12 = 5
12 years

31. 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.

32. Binding Energy The amount of energy required to break
one mole of nuclei into individual nucleons

33. Reactants and Products
Fission U fuel used in a chain reaction
Limited resource
critical mass- minimum mass to sustain chain reaction
Risk of runaway chain reaction
Produces radioactive waste products
Disposal concerns
Reaction:
Fusion- 12H and 13H used as fuel
extracted from sea water
not a chain reaction
No risk of runaway reaction
Nonradioactive waste: helium
Problem: needs temp of 200 Million K
Reaction:

34. Nuclear Power- generated by a controlled fission chain reaction
Moderators- slow neutrons down so they DO hit uranium fuel rods
Made of water, beryllium, or graphite
Intended to allow neutrons to be absorbed by uranium
Control rods- absorb neutrons to slow the chain reaction
Made of cadmium
Inserted or withdrawn to keep temp of reaction steady

35. Cooling and Shielding
Water- acts as a coolant and transfers heat between reactor and turbines that produce electricity
Steel & concrete- surround core and protect personnel by absorbing radiation

37. Other Uses of Radioactivity
Tracers
Radioactive isotopes used to track pathways
Chemistry/biology- pathways of reactions
Industry and environment- path of groundwater, durability of containers
Medicine- diagnose malfunctions