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Nuclear Change

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Title: Nuclear Change


1
Nuclear Change
  • Radiation and Radioactivity

2
(No Transcript)
3
Change
  • We have learned about
  • Physical change when atoms retain their
    identities and chemical compositions
  • Chemical change when atoms are rearranged
    forming new substances
  • We are now going to learn about
  • Nuclear change when atoms form new atoms with
    different identities and properties. A change in
    the atoms nucleus occurs!

4
Comparison of Chemical Nuclear
Chemical Reaction Nuclear Reaction
Occur when bonds are broken and formed Involve only valence electrons Small energy changes Atoms keep the same identity Occur when nuclei combine, split, and emit radiation Can involve protons, neutrons, and electrons Large energy changes Atoms are converted into different elements
5
Check for understanding
  • What type of change are the following?
  • H2O (l) ? H2O (s)
  • 2H2 (g) O2 ? 2H2O (l)
  • 21 H (g) 21H (g) ? 42He (g)
  • He (g) ? He (l)

6
Discussion
  • What do you think of when we talk about
    radioactivity?
  • Can you give some examples of materials that are
    radioactive?
  • What are some uses for radioactivity?

7
Common radioactive elements
  • Uranium
  • Plutonium
  • Radon
  • Radium
  • Bismuth
  • Carbon

8
Uses of Radioactivity
  • Medicine
  • X-rays, PET scans, MRI
  • Sterilizing bandages
  • Cancer treatment
  • Power
  • Nuclear power plants generate 1/5 of our
    electricity
  • Weaponry
  • Bombs
  • Sun
  • Industry
  • Mass spectroscopy
  • Carbon dating

9
Essential Questions
  • Who discovered radiation or radioactivity?
  • Why do we have radiation?
  • What are the different types of radiation?

10
Who discovered of radioactivity?
  • In 1895, Wilhelm Roentgen discovered the
    existence of X-rays, though the mechanism behind
    their production was not yet understood. He
    named the radioactive rays after the traditional
    unknown X.

11
Radioactivity
  • In 1896, Henri Becquerel discovered that uranium
    salts emitted rays that resembled X-rays in their
    penetrating power.

12
Radioactivity
  • Marie Curie was a French-Polish physicist and
    chemist, famous for her pioneering research on
    radioactivity.
  • She coined the word, radioactivity.
  • Marie continued work on uranium salts and in
    1898, determined that the radiation was dependent
    on the quantity of the substance not an
    interaction with other molecules.

13
Radioactivity
  • In 1899, Ernest Rutherford, a British scientist,
    began to classify radiation alpha (a), beta (b),
    and gamma (g).

14
Why do we have radiation?
  • For most stable atoms, the number of protons
    roughly equals the number of neutrons.
  • But, if an isotope has too many more neutrons
    than protons, the nucleus becomes unstable.
  • When this happens, the nucleus needs to shed some
    neutrons in the form of decay.

15
Remember - The Atom
The atom consists of two parts
1. The nucleus which contains
protons
neutrons
2. Orbiting electrons.
16
Because of isotopes, there are many types of
uranium
Mass Number
Number of protons
Number of neutrons
Mass Number
Number of protons
Number of neutrons
235
238
92
92
143
146
17
Band of Stability
  • Graph of the number of protons against the number
    of neutrons.
  • Stable atoms have the ideal ratio of protons to
    neutrons
  • Unstable will release radiation until they are
    stable

18
Isotopes
  • Unstable isotopes can become stable by releasing
    radiation in the form of energy and different
    types of particles.

19
Types of Radioactive Decay
Radioactive decay results in the emission of
either
  • Alpha decay When the nucleus spins off 2
    protons and 2 neutrons
  • Beta decay When a neutron in the nucleus
    converts to a proton and electron and then keeps
    the additional proton while shooting off the
    electron.
  • Gamma decay accompanies the other two types of
    decay but does not change the mass or charge.

20
Types of Radioactive Decay
Radiation Type Symbol(s) Charge



21
Radiation
22
Types of Radioactive decay
  • Rutherfords experiment
  • http//www.youtube.com/watch?vvuGvQjCOdr0 (144)

23
Alpha Decay
  • When an alpha particle, containing two protons
    and two neutrons, is ejected from the nucleus.
  • An alpha particle is identical to the nucleus of
    a helium atom
  • The mass number decreases by 4 and the atomic
    number decreases by 2.

24
Alpha Decay
25
Beta Decay
  • Beta particle is a fast moving electron which is
    emitted from the nucleus of an atom undergoing
    radioactive decay.
  • Beta decay occurs when a neutron changes into a
    proton and an electron.

26
Beta Decay
  • As a result of beta decay, the nucleus has one
    less neutron, but one extra proton.
  • The mass number stays the same and the atomic
    number increases by 1 and

27
Beta Decay
28
Gamma Decay
Gamma rays are not charged particles like a and b
particles.
Gamma rays are electromagnetic radiation with
high frequency.
When atoms decay by emitting a or b particles to
form a new atom, the nuclei of the new atom
formed may still have too much energy to be
completely stable.
Gamma decay does not result in the creation of a
new element!
29
Other Types of Nuclear Reactions
positron
proton -
neutron -
30
Nuclear Equations
  • Because we know that mass is conserved in every
    chemical reaction, we know that the conservation
    of matter is maintained even in radioactive
    decay!
  • So, can we use this information to write balanced
    nuclear equations?

31
Alpha Decay
unstable atom
alpha particle
New more stable element
32
Alpha Decay
33
Alpha Decay
34
Beta Decay
35
Beta Decay
36
Beta Decay
37
Check for understanding
  • Work on problems on worksheet Radioactive Decay
    Worksheet
  • Then with a partner, use the cards to solve the
    decay series of uranium. Be sure to indicate the
    type of decay in each step.

38
Radioactive Decay Rates
  • Calculating half lives

39
Radioactive decay
  • Radioactive decay rates are measured in
    half-lives
  • Half life the time required for one half of the
    nuclei to decay into its products
  • The decay continues until there is a negligible
    amount of the radioactive isotope remaining.

40
Calculating Halflives Example
  • An Isotope of cesium-137 has a half-life of 30
    years. If 1.0 g of cesium-137 disintegrates over
    a period of 90 years, how many grams of
    cesium-137 would remain?

41
The solution
Time (yrs) Mass (g)
0 1.0
30 0.5
60 0.25
90 0.125
42
Essential Question
  • So youve talked about carbon-14 dating, how does
    it actually work?

43
Carbon Dating
  • In the 1950s W.F. Libby and others (University of
    Chicago) devised a method of estimating the age
    of organic material based on the decay rate of
    carbon-14.
  • Carbon-14 dating can be used on objects ranging
    from a few hundred years old to 50,000 years old.

44
How does Carbon-14 dating work?
  • http//videos.howstuffworks.com/discovery/29401-as
    signment-discovery-carbon-dating-artifacts-video.h
    tm

45
(No Transcript)
46
Decay Rate
  • Formula
  • N N0(1/2)t/T
  • Where
  • N the remaining amount
  • N0 the initial amount
  • t elapsed time
  • T duration of the half life

47
Practice
  • 1. The half life of cobalt-57 is 270 days. How
    much of a 5.000mg sample will remain after 810
    days?
  • N ??
  • N0 5.000 mg
  • t 810 days
  • T 270 days

48
Practice
  • 2. Krypton-85 is used in indicator lights of
    appliances. The half-life of kypton-85 is 11
    years. How much of a 2.000 mg sample remains
    after 33 years?
  • N ??
  • N0 2.000 mg
  • t 33 years
  • T 11 years
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