Nuclear Chemistry Radioactive Decay

Nuclear SymbolsNuclear Symbols

Element symbol

Mass number (p+ + no)

Atomic number(number of p+)

U23592

Nuclear Reactions

A nuclear reaction is a change in the composition or make-up of the nucleus.

There are three types of nuclear reactions:

1) Fusion: Combining of nuclei into a larger nuclei

2) Fission: Splitting of an atom

3) Radioactivity: The breakdown of nuclei by giving off particles or rays.

http://www.youtube.com/watch?v=Dj4CTJy6U9M

NuclearNuclearStabilityStability

Decay will occur in such a way as to return a nucleus to the band (line) of stability.

Alpha Alpha RadiationRadiation

Alpha decay is limited to VERY large, nuclei such as those in heavy metals.

Beta Beta RadiationRadiation

Beta decay converts a neutron into a proton and electron.

e01 0

1 00

Diagram showing penetrating ability

www.epa.gov

Types of Radioactive Decay and Balancing Types of Radioactive Decay and Balancing Nuclear ReactionsNuclear Reactions

The Law of Conservation of Mass Number and the Law of Conservation of Charge allows us to predict products

in a nuclear reaction.alpha production (alpha production (He): helium nucleusHe): helium nucleus

beta production (beta production (e):e):

gamma ray production (gamma ray production ():):

The Law of Conservation of Mass Number and the Law of Conservation of Charge allows us to predict products

in a nuclear reaction.alpha production (alpha production (He): helium nucleusHe): helium nucleus

beta production (beta production (e):e):

gamma ray production (gamma ray production ():):

ThHeU 23490

42

23892

234 234 090 91 1Th Pa e

Practice!

• After completing #6 on your notes sheet, bring your it up to me so I can check your answers.

• Once your answers have been checked, get into your assigned group of approximately three students and complete the POGIL (Process Oriented Guided Inquiry Learning) activity with your partners.

EXIT TICKET: Predicting products

Predict the products for the following two nuclear equations.

1)

2)

EXIT TICKET: Predicting products

Predict the products for the following two nuclear equations.

1)

2)

Using Half-lifeThe half-life is defined as the time that it takes for one half of a sample of a radioactive element to decay into another element.

Radium-226 has a half-life of 1600 years.

Starting with a 100g sample, after 1 half-life (or 1600 years), 50g remain.

After another 1600 years, half of the 50g will remain (25g).

Sample Half-life Problem A 10 gram of sample of Iodine-131undergoes decay, what will be the mass of iodine remaining after 24 days?

The half life of iodine is determined to be approximately 8 days.

That means that 24 days is equivalent to 3 half-lifes.

The decay of 10 grams of I-131 would produce:

1.25 grams of I-131 would remain after 24 days.

Do Now

• Use a marker to write your name in LARGE PRINT on the blank side of the cardstock.

• On the back side of the cardstock label the element symbol, atomic number, and mass number.

• Define atomic number and mass number.

Carbon-14 Dating

The age of objects that were once alive can be determined by using the C-14 dating test. In this test, scientists determine how much C-14 is left in a sample and from this determine the age of the object.

From Table N we can determine that C-14 undergoes decay:

Where does the Carbon-14 come from?

C-14 is created in the atmosphere by cosmic rays.

It becomes part of living things through photosynthesis and the food chain.

When the plant or animal dies, the C-14 begins to decay.

Using C-14 to Age ObjectsBy comparing the amount of C-14 left in a sample to the amount that was present when it was alive, and using the half-life of 5700 years (Table N), one can determine the age of a sample.

Uranium-238 SeriesThe Uranium-238 Decay Series is used to determine the age of rocks.

In this series, the ratio of the U-238 to the Pb-206 is used to determine the age of the rock.

“Parent-daughter” Relationship

Aging moon rocks

NASA astronauts have retrieved 842 pounds (382 kg) of moon rocks (in many missions), which have been closely studied. The composition of the moon rocks is very similar to that of Earth rocks. Using radioisotope dating, it has been found that moon rocks are about 4.3 billion years old.

Sample Half-life Problem 2A sample of a piece of wood is analyzed by C-14 dating. The percent of C-14 is found to be 25% of what the original C-14 concentration was. What is the age of the sample?

First, let’s analyze how many half-lives have taken place.

Two half-lives have gone by while the sample decayed from the original C-14 concentration to 25% of that concentration.

Based on Table N, the half-life of C-14 is 5730 years, so…

Your turn!

On a sheet of paper, answer the following questions from your textbook. Indicate how you arrived at your answer and turn in your work for a homework/quiz grade.

Page 670

•Questions 34 (a and b), 36, 37, 38, 41, 42.

Page 671

• Questions 50, 58, 59

The End

• This is the end of the first slide show on nuclear reactions. You may continue learning about nuclear reactions by viewing the second show:

Nuclear Chemistry:

Fission and Fusion