I.

NUCLEAR CHEMISTRY Unlike other chemical reactions that involve the transfer of electrons, nuclear reactions involve changes in the nucleus II.

Transmutations-

When the atomic nucleus of one element is changed into a different element.

III. Why are certain elements or isotopes radioactive?

A. Their nuclei are

unstable

B. Nuclei become unstable when the ratio of neutrons to protons becomes greater than 1.5 (approximately) C. All elements with an atomic number greater than

83

are radioactive and all their isotopes D. Elements with atomic numbers less than 83 have some isotopes that are

radioactive

and some that are stable.

IV. Unstable Nuclei Spontaneously decay to Produce Stable nuclei by:

Alpha Decay-When an unstable nucleus emits an

alpha particle

1. Table O 2. alpha particle is a

helium nucleus

3. Symbol: 4 2 He or α 4. Example 226 88 Ra --  222 86 Rn + 4 2 He

B. Beta Decay- when an unstable nucleus emits a

beta particle

.

1. Table O 2. Beta particle is an

electron

3. Symbol: 4. Example: 234 90 Th-  234 91 Pa + 0 -1 e C. Positron Emission- When an unstable nucleus emits a

positron

1. Table O 2. Positron is a

positive electron

3. Symbol: 0 +1 e orβ + 4. Example: 37 19 K  37 18 Ar + 0 +1 e D.Gamma Radiation 1. Table O 2. Similar to high

energy x-rays

Not particles and do not have mass 3. Symbol: ɤ E. Table N shows types of decay (transmutations) exhibited by various nuclei

V. Nuclear Equations A. Balancing

1. Both mass and charge are conserved

2. The top number means mass 3. The bottom number means charge 4. The sum of the upper numbers (mass) on each side and the lower numbers (charge) on each side must be equal.

5. Example

27 13 Al + 1 0 n  24 11 Na + X Top = 28 Top = 24 so x must have a mass of 4 Bottom = 13 Bottom = 11 so X must have charge of +2 Use the periodic table or table O to identify X it is 4 2 He

VI. Transmutations A. Natural- When an unstable nuclei

spontaneously

emits an alpha particle, gamma ray, beta particle or positron.

1. All natural transmutations have only

one reactant

2. Example: 239 94 Pu  235 92 U + 4 2 He B. Artificial- When a nucleus is

bombarded

with high energy particles which brings about a change in the nucleus.

• 1. Two types a. Collision of a

charged particle with the nucleus

aa. The charged particle is accelerated to a high speed in a device called a cyclotron or synchrotron. These devices use electric and/or magnetic fields to speed up a charged particle so it can enter the nucleus bb. Example 32 15 P + 0 -1 e  32 14 Si

b. Collisions of

neutrons with a nucleus

aa. The neutron is captured by the strong force that holds protons and neutrons in the nucleus.

bb. Example 238 92 U + 1 0 n  239 92 U c. To tell the difference between artificial and natural transmutations look at the left side of the equation. Natural transmutations have a single nucleus on the left and artificial transmutations have two reactants.

VII. SEPARATING EMANATIONS 1. Done by using

electric and magnetic fields

2. In an electric field, alpha particles are deflected toward the negative electrode, beta particles are deflected toward the positive electrode and gamma rays are unaffected.

VIII. Fission and Fusion A. Fission- The splitting of a

heavy nucleus

to produce lighter nuclei by

capturing a neutron

1. Product of fission are two middle weight nuclei, one or more neutrons, and energy 2. Products are

highly radioactive

3. This is the type of nuclear reaction used in power plants

4. Example: 1 0 n + 235 92 U  142 56 Ba + 91 36 Kr+3 1 0 n + energy B. Fussion- Combining of

light nuclei

to form heavier one 1. This is the process that occurs on the sun 2. The light elements are generally

hydrogen or helium

3. Require extremely high temperatures 4. Products are

not radioactive

5. Example: 1 1 H + 1 1 H  2 1 H + 0 +1 e

IX. HALF-LIFE A. Definition-

Time required for one half of the nuclei in a given sample to decay

B. The shorter the half-life the less stable the nucleus C. Table N Example: What mass of I-131 remains after 32 days if you start with 100g.

To solve set up a table number of ½ lives time amount (g) • 0 0 100g • 1 ½ life 8 days 50g • 2 ½ lives 16 days 25 g • 3 ½ lives 24 days 12.5 g • 4 ½ lives 32 days 6.25 g

Examples: Analysis of a charred piece of coal reveals it contains ¼ of the C-14 that is found in living tissue. Assume you started with 1gram # ½ lives Time amount (g) 0 ½ lives 0 1 1 ½ life 5,770y ½ 2 ½ lives 11,540 y ¼

X. Uses of Radioisotopes A. Dating 1.

C-14

is used to date once living organisms 2.

U-238

decays into

Pb-206

and the ratio of U-238/Pb-206 is used to date rocks and other geological formations B. Chemical Tracers – a radioactive substance is used to

follow the path of a material within a system

1. P-31

Present in fertilizers and is used to follow plant process 2.

C-14

can be used to follow metabolic processes C. Industrial applications 1.

Gamma rays

can be used to measure the thickness of materials or test the strength of a weld. The more gamma rays a substance absorbs the thicker it is.

D. Medical Applications- Certain radioisotopes that are

quickly eliminated

from the body and have

short half-lives

are important as tracers in medical diagnosis.

1

. I-131

used to diagnose thyroid disorders 2.

Cobalt-60

emits large amounts of gamma arrays and can be aimed at tumors to kill cancerous cells

3. Technetium-99

is rapidly absorbed by cancer cells. It is given to patients so tumors can be detected in scans, 4.

Co-60 and Cs-137

are sources of gamma rays used to kill anthrax 5. Intense beams of

gamma radiation

can be used to irradiate foods to kill bacteria.

XI. Risks of Radiation 1. Exposure to high doses of radiation can cause

radiation sickness, cancer and mutation in cells

.

2. The by-products of nuclear power plants, spent fuel rods and equipment, are

highly radioactive with long half-lives and must be stored for many years.

3.

Safety issues

associated with nuclear power plants. Chernobyl in the Ukraine, 3 mile island in US.