Radioactivity Notes
I. Radioactivity = spontaneous breakdown of an atoms nucleus
A. Cause of radioactivity
1. atoms are made of 3 particles
electron = negative particle found orbiting the nucleus
proton = positive particle inside the nucleus
neutron = neutral particle in the nucleus
made of 1 proton + 1 electron so has no charge
2. How can all those (+) protons stay in the nucleus if they repel each other?
must be glued in by a strong force = sub atomic glue that hold the nucleus
together like cement holding bricks together in a wall, without it the wall falls apart
3. If there is not enough glue, the protons tear the nucleus apart (atoms breaking down)
hence all large atoms are radioactive (larger than 83)
B. Discovery of radioactivity
1. Henri Becquerel = discovered radioactivity in 1896
Frenchman who noticed that pitchblende ore exposed photographic film
through paper
pitchblende ore is uranium ore
2. Wilhelm Roentgen = took first x-ray 1896 in Germany
so tried with photographic film behind his wife's hand, took first x-ray
3.Marie Curie = discovered 2 elements 1899
accepted Nobel Prize in Physics
II. Characteristics of Radioactivity
A. darken photographic film
medical and film badges
B. ionize surrounding atmosphere
C. damage living things
D. found in all elements greater than 83
III. Three types of radioactivity
A. alpha particle = 2 neutrons and 2 protons
large piece of the nucleus
slow and weak due to its size
penetrate 4 cm of air only, not skin or paper or metal
B. beta particle = high speed electrons
released when alpha particle leaves, no need for the 2 electrons that went with it
fly off at near the speed of light
good penetration - 100x better than alpha particle through skin and paper and
3 cm of wood
C. gamma ray = high frequency light made from the strong force
strongest force = strongest force in universe = turns into strongest type of light
penetrates 20 ft of earth, 12 ft of rock or 10 ft or concrete or 6 inches of lead
deadly = kills your cells, if enough cells die, you die
IV. Radioactive Decay =large radioactive atoms losing an alpha particle to drop 2 spaces on the
Periodic Chart until they are no longer radioactive
A. drop 2 spaces because you loose 1 a that has 2 protons in it
so 92 becomes 90 that is still too large
so 90 becomes 88 that is still too large
so 88 becomes 86 that is still too large
so 86 becomes 84 that is still too large
so 84 becomes 82 that is not too large and is not radioactive so it stops loosing mass
82 is lead that is called stable
B. Radioactive half life = time it takes for 1/2 of a radioactive sample to breakdown into a stable
atom
1. different times because some atoms are more stable than others
Uranium has a half life of 4.5 billion years
cobalt 60 has a half life of 5.3 years
carbon 14 has a half life of 5770 years
some have half life of 0.00000001 seconds
2. Carbon 14 dating - discovered by Dr. Willard Libby
used to date famous things, Dead Sea Scrolls, Ice man, mammoths, etc.
V. Artificial Radioactivity = man made radioactivity
A. making atoms not normally radioactive into radioactive atoms
must make their nucleus too large
if add extra protons, then it changes into the next element
so must add extra neutrons, nucleus gets too fat, becomes radioactive
1. nuclear equations = show what happens to an atoms nucleus
atomic mass (protons + neutrons) on top and atomic number (number protons) on
bottom
B. Extra neutrons stuck to a nucleus make isotopes
isotope = atom with extra neutrons
1. characteristics of isotopes
a. acts the same as regular atoms neutral neutrons don't change the way they behave
b. one found in the vast majority
c. 1 extra neutron makes you heavy, 2 extra makes you radioactive
nucleus too big for the amount of glue it has
radioisotope = radioactive isotope
C. Example , use hydrogen the simplest atom
normal hydrogen (protium)
deuterium (heavy hydrogen) with extra neutron
tritium (radioactive hydrogen) with 2 extra neutrons
D. Uses of radioisotopes
tracers = radioisotopes injected into living things so that they can be followed
medicine - cobalt 60 cancer treatments
smoke detectors
sterilize food
x ray metal
nuclear bombs
energy - nuclear reactors
VIII. Uses of nuclear reactors once claimed to be "clean" power source
no smoke of fumes for the uranium heats up by itself, is not burned
A. Reactors = controlled chain reaction to produce electricity
B. submarines = can't run diesel engines under water, had to surface to charge batteries
nuclear subs can stay underwater 11 years without surfacing but crew can't
C. Surface ships
D. power plants
E. spacecraft
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Half-life Questions
Carbon-14 has a half-life of 5730 y. How much of a 144 g sample of carbon-14 will
remain after 1.719 × 10^4 years?
ANS: 18.0 g
If the half-life of uranium-235 is 7.04 × 10^8 y and 12.5 g of uranium-235 remain after
2.82 × 10^9 y, how much of the radioactive isotope was in the original sample?
ANS: 201 g
Chromium-48 has a short half-life of 21.6 h. How long will it take 360.00 g of
chromium-48 to decay to 11.25 g
ANS: 108 h
A 208 g sample of sodium-24 decays to 13.0 g of sodium-24 within 60.0 h. What is
the half-life of this radioactive isotope?
ANS: 15.0 h
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Radioactive Decay Equations
GO TO: http://www.chemteam.info/Radioactivity/Writing-Alpha-Beta.html
GO TO: http://library.thinkquest.org/27954/dequ.htm
GO TO: http://www.wwnorton.com/college/chemistry/gilbert/concepts/chapter2/ch2_2.htm
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Half-Life Graphs
GO TO: http://www.gcsescience.com/prad17-measuring-half-life.htm
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Periodic Table Review - Use your book!
Grouping the Elements of the PERIODIC TABLE
Group 1: Alkali Metals (Page 728)
Group contains:________
Electrons in the outer level (valence):______
Reactivity:____________
Other shared properties: __________________________________________________
1. Alkali metals include the three of the following elements (fill in chemical symbol)
Lithium ____ Sodium ____ Potassium _____
2. Alkali metals are the most __________________ metals. Their atoms can easily ____________
___________ their outermost electron.
3. Pure alkali metals are mostly stored in ___________ because they are so reactive.
4. In nature they are found only combined with other ____________________.
5. One example of a compound formed from alkali metals is _____________ _______________, which
flavors food.
6. Alkali metals are so soft that they can be __________________ and when put in water, they react to
form ___________________gas.
Group 2: Alkaline-earth Metals (page 734)
Group contains: __________
Electrons in the outer energy level (valence): _____
Reactivity: ______________________________________________________________
Other shared properties: __________________________________________________
1. Magnesium ______ and Calcium _____ are two familiar alkaline earth metals.
(Fill in the chemical symbols)
2. Alkaline-earth metals are not as reactive as alkali metals because it is more difficult to give away
_______ electrons than to give away ________.
3. Uses of magnesium compounds: ___________________________________.
4. Where are calcium compounds found? ___________________________
Groups 3 – 12: The Transition Metals (page 740)
Group Contains: ______
Electrons in the outer level (valence):____
Reactivity: ______________________________________________________
Other shared properties (List ALL): _______________________________________________________________
________________________________________________________________
________________________________________________________________
1. Titanium _____ Chromium _____ Iron ______ Cobalt _______ Nickel _____
Copper _____ Zinc _____ Silver______Platinum ____ Gold ____ Mercury ____
are transition metals. (Fill in symbols)
2. They are good conductors of heat and _____________. Mercury is the only metal that is
a___________ at room temperature.
3. Transition metals do not give away their electrons as __________as atoms in Groups 1 and 2 do,
making them less reactive than alkali and alkaline-earth metals.
4. The lanthanides and actinides make up two rows of transition metals that are placed at the
bottom of the table to save ____________________.
Group 13: The Boron Family (page 750)
Group Contains: _______ metalloid and ________ metals
Electrons in the outer level (valence): ____
Reactivity: ______________________
Other shared properties: _____________________________________
1. The only metalloid in the group is _________________.
2. The most common and the most abundant element in Earth’s crust. Is
____________________________________.
3. Aluminum is useful because _____________________________________
4. It is an important metal used in making
__________________________________________________________________
__________________________________________________________________
NOTE: Boron is usually found combined with oxygen and it is in Borax, a cleaning compound.
Group 14: The Carbon Family (page 754)
Group Contains: ________ nonmetal _______ metalloids and ________ metals
Electrons in the outer level (valence) ________
Reactivity: ______________________
Other shared properties: _____________________________________
1. The only nonmetal in the Carbon Family is _____________.
2. Some of the carbon compounds necessary for living things on Earth
are:____________________________________________________________.
3. The metalloids silicon and germanium are used for ______________________.
4. Because tin is not very reactive, it is used in cans to keep the steel from ________.
5. Both ______________and _____________ are natural forms of carbon (see Fig 10)
Group 15: The Nitrogen Family (page 770)
Group Contains: ________ nonmetals _______ metalloids and ________ metal
Electrons in the outer level (valence) ____
Reactivity: ______________________
Other shared properties: _____________________________________
1. Nitrogen makes up about _______ of the air you breathe. Nitrogen removed from air is reacted
with ____________ to make ammonia for _____________.
2. Phosphorus is extremely __________ and reacts with the sulfur on a match to light it. Phosphorus
is only found _________________ with other elements in nature.
Group 16: The Oxygen Family (page 774)
Group contains: ________ nonmetals _______ metalloids and ________ metal
Electrons in the outer level (valence) ______
Reactivity: ______________________
Other shared properties: _____________________________________
1. Atoms of this family have _____ valence electrons. They almost always share electrons when they
form compounds.
2. Oxygen makes up about ______ of the air you breathe. Oxygen is necessary in order for
substances to ____________.
3. Oxygen is found dissolved in ocean water, which is where _____________ fish get the oxygen they
need.
4. Sulfur is used to make ________________ _______________, the most widely used compound in the
_________________ ___________________.
Group 17:The Halogens (page 780)
Group contains: _________________
Electrons in outer level (valence) _____
Reactivity:__________
Other shared properties (list all):_______________________________________________________________
________________________________________________________________
________________________________________________________________
1. Fluorine _____ and chlorine _____ and iodine _____are three of the halogen elements. (List
symbols)
2. Halogens are very reactive nonmetals because their atoms need to gain ______________________ to
have a complete ____________ level.
3. They combine readily with other atoms, especially _______________, to gain that
___________________ __________________________.
4. The reaction of a halogen with a metal makes a ______________, such as _________________
______________________.
5. What are chlorine and iodine both used for?_____________________________
6. Although the _____________________ properties are similar, the ____________ properties are quite
_____________________.
Group 18:Noble Gases (also known as “Inert gases”) - use notes
Group contains: ____________
Electrons in outer level (valence) __________________________________
Reactivity:__________
Other shared properties (list all):________________________________________________________________
________________________________________________________________
________________________________________________________________
1. Noble Gases are _______________ nonmetals.
2. Because the atoms of the elements in this group have a __________________ ________ of electrons
in their outer level the do not need to ____________ or _______________ any electrons.
3. They do not _________________with other elements under normal conditions.
4. Earth’s atmosphere is almost _____% argon.
5. Look at Figure 8 on pg. 207. What is another popular use of noble gases?
________________________________-
Hydrogen Stands Alone
Electrons in outer level (valence) _____
Reactivity:__________
Other properties (list all):____________________________________
________________________________________________________________
1. Hydrogen is the most _________________ element in the universe. It is found in large amounts, in
__________________.
2. When hydrogen joins with other atoms, it gives away its ______ electron.
3. Hydrogen’s reactive nature makes it useful as a ____________ in rockets.
4. Why is hydrogen set apart in the periodic table?
_________________________________________________________
5. Hydrogen is placed above Group 1 because, like alkali metals, hydrogen has
_____________________________________________________________.
6. However, hydrogen’s physical properties are more like the properties of _________________ than
_______________.
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Also review in your notebook:
Ionic and Covalent Compounds
Density
Buoyancy
Viscosity
Metric Conversions
Significant Figures
Accuracy and Precision