1. Isotopes and Radioactivity
Chapter 7 Lesson 2
Isotopes and Radioactivity

2. Left
What’s the difference between the two atoms in Figure 12?

3. Isotopes – Different Numbers of Neutrons
What’s the difference between the two atoms in Figure 12?
O-17 has one extra neutron
These two atoms are called Isotopes

4. How Many Neutrons?
Isotopes with more neutrons are heavier than isotopes with fewer neutrons.
Lets calculate the number of neutrons in a Carbon-14 atom:

5. How many neutrons? Left How many neutrons are in Carbon-12 atoms?

6. How many neutrons? How many neutrons are in Carbon-12 atoms?

7. What determines properties?
Chemical properties are determined by the number of valence electrons an atom has.
Valence electrons determine what type of bond an element will form.
Do isotopes have similar chemical properties??

8. What determines properties?
Chemical properties are determined by the number of valence electrons an atom has.
Valence electrons determine what type of bond an element will form.
Do isotopes have similar chemical properties??
Yes they do, because they have the same number of electrons.

9. What is radioactive decay?
The three isotopes of Carbon have similar properties, but C-14 is radioactive.

10. What is radioactive decay?
When radioactive decay occurs, an unstable atomic nucleus changes into another nucleus by releasing one or more particles and energy.
Stability increases and a different element is formed. (See Figure 15 on page 303)

11. Uses of Radioactive Decay
Left
Uses of Radioactive Decay
Look on page 304 at the bottom.
List 3 ways that we have found to use radioactive decay

12. Uses of Radioactive Decay
Look on page 304 at the bottom.
List 3 ways that we have found to use radioactive decay:
Medical imaging
Detection of cancer cells
Killing of cancer cells
Preservation of food

13. Radioactive Elements and the Periodic Table
Radioactive elements = elements that have only radioactive isotopes
Radioactive Elements are HEAVY so they are found near the bottom of the periodic table (See figure 18 below)

14. Half-life Isotopes decay at very different rates
Half-life= the time it takes for half of the original sample to decay
Uranium-235 has a half life of 713 million years!
How many grams would be left after another 713 million years?

15. Half-life Left Erbium has many isotopes:
1. How many seconds is the half-life for Er-147?
2. How much time would it take for a 100g sample of Er-145 to decay to a 25g sample?
3. How much time would it take for a 200g sample of Er-169 to decay to a 100g sample?
Half-Lives of Erbium
Isotope
Half-Life
Er-145
0.9 s
Er-147
2.5 s
Er-154
3.73 min
Er-156
19.5 min
Er-158
2.29 h
Er-169
9.40 days

16. Half-life Erbium has many isotopes:
1. How many seconds is the half-life for Er-147? 2.5 s
2. How much time would it take for a 100g sample of Er-145 to decay to a 25g sample? ( = 1.8 s)
3. How much time would it take for a 200g sample of Er-169 to decay to a 100g sample? 9.40 days
Half-Lives of Erbium
Isotope
Half-Life
Er-145
0.9 s
Er-147
2.5 s
Er-154
3.73 min
Er-156
19.5 min
Er-158
2.29 h
Er-169
9.40 days