1. Review and Radioactivity
Chpt 18

2. Review
Atomic # = # p (must equal #e)-form electrically neutral atom…….if they don’t equal (called ion)
Isotope…same p/e…neutrons are different in same element….ex C12 or C14 as is mass #
Energy levels are found on side of PT (period)…full shell ends at group 18..then fills up again

3. Radioactivity
Nucleus contains almost all the mass of an atom (p/n have all mass)…electrons are negligible (little mass)
EX. Marble sitting in middle of football field
When a nucleus decays (loses particles) matter and energy is given off (lots of energy)
This happens spontaneously (naturally)
Occurs mostly in large elements because attraction forces aren’t as strong to hold particles within nucleus
Large nuclei are unstable and decay more than small nuclei

4. Nuclear Decay
When unstable nuclei decay…particles and energy (called nuclear radiation) are emitted (given off)
3 types of nuclear radiation
A. Alpha-particles
B. beta-particles
C. gamma-electromagnetic wave

5. Alpha Very massive particle (made of p/n) Most electric charge
Lose energy quickly
Least penetrating power-stopped by paper
Charge =+2…….mass + 4
Transmutation occurs=changing one element to another through nuclear decay

6. symbol

8. Beta particle An electron is emitted (given off) from nucleus decay
Much faster and penetrate more than alpha
Go thru paper….stopped by foil
Undergoes transmutation like alpha
Charge is -1………mass (small)

9.
I e- = Xe

10. Gamma Rays Most powerful and penetrating of all No mass and no charge
Given off by nucleus during alpha/beta decay
Lead and concrete can only stop gamma rays

13. Half-life
The amount of time a radioactive isotope takes for half the nuclei of a sample to decay
Very hard stuff so pay attention
Used in science to date rocks, fossils, bones..etc

14. Problems examples
The half life of calcium is 10 days. How much of a 100 g sample will remain after
A. 20 days
B. 30 days
C. 40 Days
D. 50 days

15. Another look
A sample of Phosphorous-18 originally has 30g. Phosphorous-18 has a half life of 2,000 years. In _______________ years, how many grams would remain undecayed?
A. 2,000 yrs
B. 4,000 yrs
C. 8,000 yrs

16. Another look
At the end of 45 days, 100 g of Carbon-14 has decayed to 12.5 g. What is the ½ life of Carbon 14?

17. What is the half life of the radioisotope?
Gieger counter data
Time in days
0.0
5.0
10.0
15.0
Counts per second
1000
2000
3000
4000
What is the half life of the radioisotope?