Nuclear Chemistry

Tiny little living space, awesome power!

Dr. Melinda Oliver

CHM 112

Bishop State Community College

A short review of the nucleus

Radioactivity-unstable atomic nuclei

The band of stability shows the effect of the ratio of neutrons (N) over protons (P) N/P

Different sized elements have predictable patterns of radioactivity if the N/P does not fall along the band of stability.
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Practice Problems

1. Indicate the number of protons and neutrons in the following nuclei. (a) Te-124, (b) Cl-37, (c) thorium-232.

2. Write balanced nuclear equations for the following transformations: (a) bismuth-213 undergoes alpha decay, (b) nitrogen-13 undergoes electron capture, (c) technicium-98 undergoes electron capture, (d) gold-188 decays by positron capture.

3. What particle is produced during the following decay processes: (a) sodium-24 decays to magnesium-24, (b) mercury-188 decays to gold-188, (c) iodine-122 decays to xenon-122, (d) plutonium-242 decays to uranium-238.

4. A radioactive decay series that begins with thorium-232 ends with the formation of the stable nuclide lead-208. How many alpha-particle emissions and how many beta-particle emissions are involved in the sequence of radioactive decays?

5. Each of the following nuceli undergoes either beta decay or positron emission. Predict the type of emission for each: (a) tritium, 3 1H; (b) 8938Sr, (c) iodine-120, (d) silver-102.

6. In 1930 the American physicist Ernest Lawrence designed the first cyclotron in Berkeley, California. In 1937 Lawrence bombarded a molybdenum target with deuterium ions, producing for the first time an element not found in nature. What was this element? Starting with molybdenum-96 as your reactant, write a nuclear equation to represent this process.

7. Complete and balance the following nuclear equations by supplying the missing particle:

(a) N-14 + 4 alpha → ? + H-1

(b) K-40 + beta (orbital electron) → ?

(c) ? + alpha → H-1 + S-30i

(d) Fe-58 + 2neutrons → ? + Co-60

(e) U-235 + neutron → ? + X-135e +2neutrons

One of the four fundamental forces in nature is the Strong Nuclear Force

The nucleus occupies very little space in an atom but in that space are protons which "do not like each other" so how does the nucleus stay together? The answer is in the neutrons. The neutrons only add attractive forces while protons bring both repulsive (between protons) and attractive forces (between protons and neutrons) to the nuclear living space. The attractive force in the nucleus is the strong nuclear force which holds the tiny nucleus intact and is unleashed should the nucleus be disrupted in the case of nuclear fission or fusion.

The mass defect-the most famous science equation!

You have learned that in chemical reactions, mass is conserved. For the most part, this is correct. There are very minimal mass differences that using Einstein's famous equation would translate into small amounts of energy. That is what the equation is about-the direct relation between mass and energy. There is a great book on this equation. The history behind every piece (even the equal sign). For those interested:

So, in typical chemical reactions some of the mass (about 9.9 x 10^-9 g for the combustion of one mole of methane) is lost but this is pretty minimal. However, plug it into the equation and you do get some energy out of it.

The mass lost in nuclear reactions is much larger. For a typical alpha emission:

the mass lost (product mass-reactant mass) is -0.0046 g. Plug this into the equation (convert mass into kg so energy comes out in joules) and you end up with -4.11 x 10^11 J, a pretty significant amount of energy.

Practice Problems

1. An analytical laboratory balance typically measures masses to the nearest 0.1 mg. What energy change would accompany the loss of 0.1 mg of mass?

2. The isotope nickel-62 has the largest binding energy per nucelon of any isotope. Calculate this value from the atomic mass of nickel-62 (61.928345) and compare it with the value given for iron-56 (1.41 x 10^-12 J/nucleon).

Practice Problems

1. It takes 5.2 min for a 1.000 g sample of francium-210 to decay to 0.250 g. What is the half-life of francium-210?

2. A wooden artifact from a Chinese temple has a carbon-14 activity of 38.0 counts per minute as compared with an activity of 58.2 counts per minute for a standard of zero age. From the half-life for carbon-14 decay, 5715 yr, determine the age of the artifact.

3. The half-life for the process 238U --> 206Pb is 4.5 x 109 yrs. A mineral sample contains 75.0 mg of 238U and 18.0 mg of 206Pb. What is the age of the mineral?

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Online Radioactivity Lab

See link above for instructions.

What Else Can You Do to Help Your Understanding?

Chemistry is a subject that must be practiced everyday if possible. Work through the lecture examples stopping the video clips and then restarting to check yourself. Take advantage of the online homework in Mastering Physics to give you the practice you need to be successful. DO NOT PROCRASTINATE! Email me with questions!!

Have Questions Later?

If you have trouble opening any links, or just need some clarification...

Dr. Melinda Oliver
Bishop State Community College