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Name _________________________________________________________

Name _________________________________________________________

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Chapter 25 – Nuclear Chemistry

This packet contains background and explanatory information on Nuclear Chemistry in addition to practice handouts. The information should be read and used to complete all of the practice included. I will be collecting this packet and giving points for the completion of the contents. You may want to consult other online resources for addition explanations and examples if needed. You will be given a 30 point quiz at the completion of the packet. You must complete the packet and take the quiz by 10/20/2018.

Chapter Learning Targets I CAN…

· Compare and contrast alpha, beta, and gamma radiation.

· Identify alpha decay, beta decay, fission, and fusion reactions.

· Balance nuclear equations.

· Solve half-life calculations.

Part I: Radioactivity - What is it?

Go to the following webpage for more details and videos: http://www.darvill.clara.net/nucrad/index.htm

All substance are made of atoms. These have electrons (e) around the outside, and a nucleus in the middle. The nucleus consists of protons (p) and neutrons (n), and is extremely small. (Atoms are almost entirely made of empty space!)

In some types of atom, the nucleus is unstable, and will decay into a more stable atom. This radioactive decay is completely spontaneous. The energy that is released from the nucleus of the atom is radiation.

When an unstable nucleus decays, there are three ways that it can do so. It may give out:-

· an alpha particle (we use the symbol )

· a beta particle (symbol )

· a gamma ray (symbol )

Many radioactive substances emit particles and particles as well as rays. In fact, you won't find a pure source: anything that gives off rays will also give off and/or too.

A. Alpha Particles – More Information

B. Beta Particles – More Information

C. Gamma Particles – More Information

Summary:

Particles that ionize other atoms strongly have a low penetrating power, because they lose energy each time they ionize an atom. Therefore, alpha particles are easy to stop and gamma rays are hard to stop.

Assignment: Use the information presented in “Part I: Radioactivity – What is it?” to complete the table below.

Type of Radiation

Alpha particle

Beta particle

Gamma ray

Symbol (show all variations)

Mass (atomic mass units)

Charge

Speed

Ionizing ability

Penetrating power

Stopped by

Sources of Radioactivity:

Part II: Isotope Notation

Isotope Notation includes additional information about an isotope. In addition to the chemical symbol, the mass number and the atomic number are included. This allows information about the nucleus to be determined.

Example:

The isotope notation for an atom of uranium-238 is:

· The mass number is 238.

This is the sum of protons and neutrons in the nucleus. (Protons + Neutrons = Mass)

· The atomic number is 92.

This is the quantity of protons (and electrons) in the atom. It also leads to the chemical symbol for the isotope.

· The chemical symbol “U” is obtained from the name or by looking up the atomic number on the periodic table.

PRACTICE: Answer the following questions pertaining to each isotope.

1. a) What is the name of this isotope? ____________________________

b) What is the mass of this isotope? ____________________________

c) How many protons are in this isotope? ________________________

d) How many neutrons are in this isotope? _______________________

2. iron-56 a) What is the isotope notation for this isotope? ___________________

b) What is the mass of this isotope? ____________________________

c) How many protons are in this isotope? ________________________

d) How many neutrons are in this isotope? _______________________

Part III: Nuclear Decay Reactions – Alpha and Beta

A. The Band of Stability (The “Stability Line”)

As the Atomic Number (that's the number of protons) increases, atoms seem to need more neutrons. Carbon-12 has 6 protons and 6 neutrons, while Uranium-238 has 92 protons and 146 neutrons. Once we get more than 82 protons (that's Lead), the nuclei are no longer stable, and we're into radioactive elements. Elements with more than 92 protons are so unstable that they don't exist naturally, and have to be made by us in nuclear reactors. An example is Americium-241 (95 protons), which emits alpha particles and is used in smoke detectors.

B. Identifying Alpha and Beta Decay Reactions Video Link: Alpha and Beta Decay

Alpha Decay:

Alpha decay is one process that unstable atoms can use to become more stable. During alpha decay, an atom's nucleus sheds two protons and two neutrons in a packet that scientists call an alpha particle.

Since an atom loses two protons during alpha decay, it changes from one element to another. For example, after undergoing alpha decay, an atom of uranium (with 92 protons) becomes an atom of thorium (with 90 protons).

The reaction above would be written as: (with the He representing the alpha particle)

Beta decay:

During beta decay, a neutron breaks apart into a proton and an electron. The electron is emitted and is called a beta particle. This reaction would be written as:

C. Balancing Alpha and Beta Decay Reactions

All nuclear reactions are balanced when the total number of reactant protons and neutrons is equal to the total number of product protons and neutrons. Your goal is to use this concept to determine the missing isotope in the nuclear equations below. After balancing, identify each as being either alpha or beta decay.

Watch the following video tutorial: Writing Alpha and Beta Decay Reactions

Examples:

1.Rn ( Po + ____

2.Th ( Pa + ____

Decay type __________________ Decay type __________________

Practice Equations:

1.Bi ( He + ____

3.Sr ( Y + ____

Decay type __________________ Decay type __________________

2.Np ( e + ____

4.Th ( Ra + ____

Decay type ________________ Decay type _______________

Part IV: Decay Chains (also known as Series Decay)

Most radioactive elements do not decay directly to a stable state, but rather undergo a series of decays until eventually a stable isotope is reached. A parent isotope is one that undergoes decay to form a daughter isotope. The daughter isotope may be stable or it may decay to form a daughter isotope of its own.

Complete the decay series for uranium-238 described below. You will need to write the complete reaction for each step of the decay. Each reaction is identified as being either an alpha decay reaction, releasing a helium isotope, or a beta decay reaction, releasing an electron. Write a reaction based upon this reaction type. The daughter isotope from one step becomes the parent isotope for the next step, hence becoming a decay chain. This decay requires 14 steps with the final daughter isotope being lead-206.

Watch the following video to assist you in the task: Series Decay Example

Step 1: alpha decay of uranium-238 ______________________________________________

Step 2: beta decay reaction ___________________________________________________________


Step 4: alpha decay reaction ___________________________________________________________










Step 14: alpha decay reaction (The daughter of this reaction should be lead-206!)

___________________________________________________________

Part V: Synthetic Decay Reactions – Fission and Fusion

Watch the following video on nuclear fission and fusion: Fission and Fusion Reactions Video

In addition to being able to balance and identify alpha and beta reactions, you must also be able to balance and identify fission and fusion reactions.

A. Fission: Fission is the process of splitting an atom. This occurs when a neutron is “absorbed” by a large, unstable isotope. This causes the isotope to split into two smaller isotopes and to emit free (or extra) neutrons that cause subsequent fission reactions. This is called “self-sustaining” chain reactions. They release nuclear energy at a controlled rate in a nuclear reactor or at a very rapid uncontrolled rate in a nuclear weapon.

All fission reactions show a large isotope reacting with a neutron to produce two smaller isotopes and free neutrons.

Example:

Pu + n ( 3 n + Ru + Sn

B. Fusion: Nuclear fusion is the process by which multiple small atomic nuclei join together to form a heavier nucleus. It is accompanied by the release or absorption of energy. Fusion occurs naturally in stars and has been produces synthetically for hydrogen bombs.

Example:

Li + Li ( C

For balancing these fission and fusion reactions, the same rules apply – the total number of protons and neutrons must be same on both sides of the equation.

Watch this tutorial video for help balancing fission reactions: Balancing Fission Reactions

Examples:

1.U + n ( 3 n + Kr + _____

2. _____ + H ( He

Decay type _________________ Decay type ___________________

Assignment: Complete the “Practice Equations” below by balancing and identifying the type of reaction – fission or fusion.

Practice Equations:

1. H + H ( _____

3. U + n ( Sr + _____ + 3 n

Decay type ________________ Decay type ______________________

2. U + n ( La + _____ + 3 n

4. H + _____ ( He

Decay type _________________

Decay type ______________________

Part VI: Half-Life Calculations

When radioactive isotopes decay, they do so exponentially. Their rate of decay is determined through an understanding of half-life. Half-life is the amount of time it takes for half of the atoms of an unstable isotope to decay. It is important to know that all isotopes have different half-lives and that the length of the half-life is related to the stability of the isotope. Those with short half-lives are more unstable than those with long half-lives.

Your goal is to be able to perform various half-life calculations. When solving these problems, you must take into consideration the amount of sample, the length of the half-life, and the amount of time the sample is decaying. Remember…over the course of one half-life, the amount of sample reduces by half. Use the examples below to solve the practice calculations that follow. I use a table to organize my information, but you may use any approach that works for you. Show your work!!

Examples: Follow along and show work from this video: Half life practice problems

1. The half life of Zn-71 is 2.4 minutes. If you start with 100g of Zn, how many grams would be left after 7.2 minutes have passed?

Solution (

2. The half life of Pd-100 is 4 days. After 12 days a sample has been reduced to a mass of 4g. What is the starting mass (amount)?

Solution (

3. How long will it take for a 64g sample of Rn-222 that has a half life of 3.8 days to decay to 8g?

Solution (

** Use these above examples to complete the “Practice Problems” on the back of this page.

Practice Problems – Half Life Calculations

1. Polonium-218 has a half life of 3.05 minutes. If an initial sample contains 2500 atoms, how long will it take for the sample to decrease to 78.125 atoms?

2. Lead-210 has a half life of 19.4 years. If an initial sample contains 25.0 grams, how much will remain after 97.0 years?

3. How long will it take for a 6.54 g sample of Protactinium-234 to decay to 0.40875 grams if it has a half life of 1.18 minutes?

4. How long would it take for a sample of Rn-222 containing 750 atoms to decay down to 23.4375 atoms if the half life of the isotope is 3.8 days?

5. The half life of U-238 is 4.5 billion years. After 22.5 billion years a sample has been reduced to a mass of 17g. What is the starting mass of the sample?

Alpha particles are made of 2 protons and 2 neutrons.

This means that they have a charge of +2, and a mass of 4�(the mass is measured in "atomic mass units", where each proton & neutron=1)�We can write them as � INCLUDEPICTURE "http://www.darvill.clara.net/nucrad/images/alpha42.jpg" \* MERGEFORMATINET ��, or, because they're the same as a helium nucleus, � INCLUDEPICTURE "http://www.darvill.clara.net/nucrad/images/He42.jpg" \* MERGEFORMATINET ��.

Alpha particles are relatively slow and heavy.

They have a low penetrating power - you can stop them with just a sheet of paper.

Because they have a large charge, alpha particles ionize (pull electrons from) other atoms strongly.

Beta particles have a charge of minus 1 (-1), and a mass of about 1/2000th of a proton. This means that beta particles are the same as an electron. �We can write them as � INCLUDEPICTURE "http://www.darvill.clara.net/nucrad/images/betaminus.jpg" \* MERGEFORMATINET ��or, because they're the same as an electron, � INCLUDEPICTURE "http://www.darvill.clara.net/nucrad/images/eminus.jpg" \* MERGEFORMATINET ��, written in isotope notation as �

They are fast, and light.

Beta particles have a medium penetrating power - they are stopped by a sheet of aluminum or plastics.

Beta particles ionize atoms that they pass, but not as strongly as alpha particles do.

Gamma rays are waves, not particles. �This means that they have no mass and no charge. So we sometimes write � INCLUDEPICTURE "http://www.darvill.clara.net/nucrad/images/gamma00.jpg" \* MERGEFORMATINET ��.

Gamma rays are extremely fast and have a high penetrating power - it takes a thick sheet of metal such as lead, or concrete to reduce them significantly.

Gamma rays do not directly ionize other atoms, although they may cause atoms to emit other particles which will then cause ionization.

We don't find pure gamma sources - gamma rays are emitted alongside alpha or beta particles. Strictly speaking, gamma emission isn't 'radioactive decay' because it doesn't change the state of the nucleus. It just carries away some energy.

We are all exposed to radioactivity every day of our lives. As you can see from the pie chart to the right, most of the radioactivity we are exposed to on a daily basis comes from natural sources such as radon gas, our own bodies, the ground, and cosmic rays (gamma rays from space). We have grown up on a planet which has, in places, quite a high level background radiation, and life on Earth has evolved to cope with this. Our cells have self-repairing mechanisms which allow them to survive relatively unscathed.

When we plot a graph of "Number of neutrons" against "Number of protons", we find that stable elements lie on a "stability line". Elements which are not on this line are unstable, and we find that they tend to undergo alpha-decay or beta-decay and get closer to the stability line. They may take several steps in order to achieve this, thus we observe decay chains (also known as series decay) for most radioactive elements.

Radioactive decay is totally spontaneous. There is no way to tell if an individual atom is about to "pop", nor is there any way to predict when it's going to do it. However, when we're dealing with huge numbers of atoms, you can confidently predict how many will decay on average in any given period of time.

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name · web viewcompare and contrast alpha, beta, and gamma radiation. identify alpha decay, beta...

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