chem hw 14
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Review Question 1:
What has the greatest penetrating power - alpha particles, beta particles or gamma rays?
Gamma rays have the most penetrating power.
Is radioactivity on Earth relatively new? Defend your answer.
Radioactivity is as old as the earth. Radioactive elements are deep within the earth since its beginning.
Distinguish between a rad and a rem?
A rad is a dosage of radiation, a rem is a dosage based on potential damage.
Why doesn't the repulsive electric force of protons in the atomic nucleus cause the protons to fly apart?
The strong nuclear force holds the nucleons in the nucleus. The strong force is much stronger than the electrostatic force between the protons.
How are the strong nuclear force and the electric force different from each other?
The strong force is very strong and short range. The electrostatic force is long range and weak compared to the strong force.
What role do neutrons play in the atomic nucleus?
The presence of neutrons adds to the strong force attraction without any electrostatic force, because neutrons have no charge.
What is meant by the half-life of a radioactive sample?
The half-life is the time for half the sample to decay to another element.
What change in atomic number occurs when a nucleus emits an alpha particle?
A beta particle?
The atomic number is reduced by two in an alpha decay. The atomic number is increased by one in a beta decay.
Which is radioactive, carbon-12 or carbon-14?
Carbon-14 is radioactive.
Why is there more carbon-14 in living bones than in once-living ancient bones of the same mass?
The carbon-14 is radioactive and is decaying, therefore depleting all the time.
Why is carbon-14 dating useless for dating old coins but not old pieces of cloth?
The coins don't contain carbon-14 because they are not or never were living. The cloth originally came from a living thing, so carbon-14 dating works.
Is it possible for a hydrogen necleus to emit an alpha particle? Defend your answer.
It is impossible for a hydrogen atom to eject an alpha particle for an alpha particle is composed of a pair of hydrogen isotopes (deuferium). It is equally impossible for a one-kilogram melon to spontaneously break into four one-kilogram melons.
Just after an alpha particle leaves the nucleus, would you expect it to speed up? Defend your answer.
An alpha particle undergoes an acceleration due to mutual electric repulsions as soon as it is out of the nucleus and away from the attracting nuclear force. This is because it has the same sign of charge as the nucleus. Like charges repel.
How do the electric charges of alpha particles, beta particles and gamma rays differ from one another?
Alpha rays have 2 protons and 2 neutrons, beta rays have 1 electron and gamma rays have no charge.
Which type of radiation -- alpha, beta, or gamma -- results in the greatest change in mass number? The greatest change in atomic number?
Alpha radiation decreases the atomic number of the emitting element by 2 and the atomic mass number by 4. Beta radiation increases the atomic number of an element by 1 and does not affect the atomic mass number. Gamma radiation does not affect the atomic number or the atomic mass number. So alpha radiation results in the greatest change in atomic number and hence change and mass number as well.
If an atom has 104 electrons, 157 neutrons, and 104 protons, what is the approximate atomic mass? What is the name of the elements?
The mass of the elements is 157 + 104 = 261. Its atomic number is 104, a transuranic element recently named rutherfordium.
When the isotope bismuth-213 emits an alpha particle, what new element results?
What new element results if it instead emits a beta particle?
- Bismuth-213 becomes Thallum-209 when it emits an alpha particle.
- Bismuth-213 becomes Polonium-209 when it emits a beta particle.
What are the atomic number and atomic mass of teh element formed when Po-218 emits a beta particle? What are they if the polonium emits an alpha particle?
After beta emission from polonium, the atomic number increases by 1 and becomes 85, and the atomic mass is uncharged at 218. However, if an alpha particle is emitted, the atomic number decreases by 2 and becomes 82, and the atomic mass decreases by 4 and drops to 214.
Your friend says that the helium used to inflate balloons is a product of radioactive decay. Another friend says no way. With whom do you agree?
Agree with your friend that attributes helium to alpha particles. Its true, alpha particles emitted by radioactive isotopes in the ground slow down and stop capture two electrons and become heliumatoms. Our
Why is carbon-14 dating not accurate for estimating the age of materials more than 50,000 years old?
Radioactive decay rates are statistical averages of large numbers of decaying atoms. Because of the relatively short half life of the carbon-14, only trace amounts would be left after 50,000 years -- too little to be statistically accurate.
The isotope cesium-137, which has a half life of 30 years, is a product of nuclear power plants. How long will it take for this isotope to decay to about 1/16th its original amount?
After 30 years, half is left. After 60 years, 1/4 is left. After 90 years, 1/8th is left. Finally after 120 years, 1/16th is left.
A certain radioactive element has a half life of one hour. If you start with a one gm sample of the element at noon, how much is left at 3 PM? At 6 PM? At 10 PM?
At 1 PM 1/2 gm left. At 2 PM 1/4 gm is left. At 3 PM 1/8th is left. At 4 PM, 1/16 is left. At 5 PM 1/32 is left. At 6 PM 1/64 is left. At 7 PM 1/128 is left. At 8 PM 1/256 is left. At 9 PM 1/512 is left. Finally at 10 PM, 1/1024 gm is left.
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