1. Unit 6 Review Questions

2. For 238U, give the A) atomic number B) mass number C) number of neutrons92
238
146

3. Which number of neutrons in a sodium atom would be the most stable: 4, 12, 18, or 23 ?
Since Sodium is a small element (less than 30 protons), a 1:1 ratio will be most stable.
Sodium has 11 protons, so of the choices, 12 neutrons would hold together best.

4. Which isotope of iodine would you predict to be the most stable?
53I has 53 protons and 0 neutrons, so it is obviously unstable.
Since Iodine is a larger element (more than 30 protons), 108I (close to a 1:1 ratio) will not be enough to hold the nucleus together.
159I has 53 protons and 106 neutrons (a 2:1 ration). This is too many neutrons to be stable……..
129I has 53 protons and 76 neutrons. This is more than 1:1, but much less than a 2:1 ratio, so it must be the most stable choice.

5. How many electrons and protons does Sr+2 have?
Sr always has 38 protons.
The “positive 2” means that it has 2 more protons than electrons
Therefore the answer is 36 electrons.

6. List the three types of radiation and put them in order of increasing harmfulness.
Alpha – least harmful (blocked by clothing)
Beta – more harmful (penetrates a few cm into skin)
Gamma – most harmful (goes through to internal organs)

7. What does an alpha particle consist of ?
2 protons and 2 neutrons

8. Which of the following are the same element?
are all the same element because they all have the
same number of protons (9)

9. What element has the electron configuration [Ar]4s13d10 ?
Copper.
Since it is 4s1, we know it is a d9 rule-breaker.
If it were Zn, it would have been 4s23d10

10. Write an equation showing the beta decay of Ra-227.

11. If Radium-245 has a half life of 5 minutes, how long will it take a 36g sample to only have 4.5 grams remain?
15 minutes

12. It is jumping from level 4 to level 2.
Using your hydrogen spectrum sheet on page 19, which electron jump produces an energy with a wavelength 4800 Angstroms ?
Looking at the line spectra on the top of page 19, you can see that the line at 4800 Angstroms is labeled “b” in the Balmer series.
Looking at the chart at the bottom, find the arrow labeled “b” in the Balmer series
It is jumping from level 4 to level 2.

13. Define a space orbital
A space orbital is defined as region where an electron is located with 90% probability.

14. Explain what causes the light to be given off in a “neon” light.
Energy from the electricity is absorbed by some electrons and they jump up to higher energy levels (excited state).
When the electrons jump back down from the excited to the ground state, they release energy.
Some of that energy released is in the form of visible light.

15. Give the set of quantum numbers for the last electron placed in fluorine
Principle Quantum Number = 2
Angular Momentum Quantum Number = p (or 1)
Magnetic Quantum Number = y
Spin Quantum Number = -1/2

16. Which of the following is an example of a nuclear fusion reaction?
238U  234Th + 4He
236U  90Sr + 143Xe + 3 1n
1H +3H  4He
210Po  210At + 0e-
# 1 is an alpha decay
# 2 is a nuclear fission rxn
# 4 is beta decay

17. Where does all of the energy come from in nuclear reactions?
In nuclear reactions, MASS IS LOST !!!!
The mass that is lost is converted into HUGE amounts of energy as calculated by Einstein’s E=MC2 equation.

18. List 2 advantages and 2 disadvantages of nuclear fission power plants.
They do not produce any CO2, NOx, or SOX. Therefore, they do not contribute to acid rain or global warming.
Only a small amount of fuel is needed to produce a lot of energy.
It reduces our dependency on foreign oil.
Disadvantages:
Radioactive waste is a byproduct which is dangerous for 1000’s of years.
An accident has the potential to release harmful radiation into the environment.

19. H Be sure to review main concepts from the “It Glows” lab and the “Fireworks” Lab.

20. The following slides may contain information that was not covered this course. If your instructor told you to cross off “Define and Calculate wavelength, frequency, and energy” from your Unit 6 cover sheet, then do not worry about the following slides.

21. What is the frequency of a wave whose wavelength is 4560 Angstroms
What is the frequency of a wave whose wavelength is 4560 Angstroms? (1 Angstrom = 1 x meters)
6.58 x 1014 /s

22. Using your hydrogen sprectrum sheet, which electron jump produces an energy of 1.06 x 10-19 J?
Using the energy formula, we can calculate the frequency as 1.60 x 1014 /s
Using the other formula, we solve for wavelength and get 1.88 x 10-6m
Converting to Angstroms, we look on the spectra on page 19 to see this is “a” in the Paschen series
Using the bottom chart, we see that “a” in the Paschen series is jumping from level 4 to level 3