Title: Nuclear Change
1Nuclear Change
- Radiation and Radioactivity
2(No Transcript)
3Change
- 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!
4Comparison 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
5Check 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)
6Discussion
- 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?
7Common radioactive elements
- Uranium
- Plutonium
- Radon
- Radium
- Bismuth
- Carbon
8Uses 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
9Essential Questions
- Who discovered radiation or radioactivity?
- Why do we have radiation?
- What are the different types of radiation?
10Who 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.
11Radioactivity
- In 1896, Henri Becquerel discovered that uranium
salts emitted rays that resembled X-rays in their
penetrating power.
12Radioactivity
- 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.
13Radioactivity
- In 1899, Ernest Rutherford, a British scientist,
began to classify radiation alpha (a), beta (b),
and gamma (g).
14Why 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.
15Remember - The Atom
The atom consists of two parts
1. The nucleus which contains
protons
neutrons
2. Orbiting electrons.
16Because 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
17Band 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
18Isotopes
- Unstable isotopes can become stable by releasing
radiation in the form of energy and different
types of particles.
19Types 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.
20Types of Radioactive Decay
Radiation Type Symbol(s) Charge
21Radiation
22Types of Radioactive decay
- Rutherfords experiment
- http//www.youtube.com/watch?vvuGvQjCOdr0 (144)
23Alpha 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.
24Alpha Decay
25Beta 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.
26Beta 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
27Beta Decay
28Gamma 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!
29Other Types of Nuclear Reactions
positron
proton -
neutron -
30Nuclear 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?
31Alpha Decay
unstable atom
alpha particle
New more stable element
32Alpha Decay
33Alpha Decay
34Beta Decay
35Beta Decay
36Beta Decay
37Check 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.
38Radioactive Decay Rates
39Radioactive 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.
40Calculating 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?
41The solution
Time (yrs) Mass (g)
0 1.0
30 0.5
60 0.25
90 0.125
42Essential Question
- So youve talked about carbon-14 dating, how does
it actually work?
43Carbon 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.
44How does Carbon-14 dating work?
- http//videos.howstuffworks.com/discovery/29401-as
signment-discovery-carbon-dating-artifacts-video.h
tm
45(No Transcript)
46Decay 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
47Practice
- 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
48Practice
- 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