1. CHAPTER 24 Nuclear Energy
I. Radioactivity
(p ) 1 1

2. A. Definitions Radioactivity
emission of high-energy radiation from the nucleus of an atom
Nuclide
nucleus of an isotope
Transmutation
process of changing one element into another via nuclear decay

3. B. Nuclear Decay Why nuclides decay…
to obtain a stable ratio of neutrons to protons
Stable
Unstable
(radioactive)

4. C. Half-life Half-life (t½)
time it takes for half of the nuclides in a sample to decay
Example Half-lives
polonium seconds
lead hours
iodine days
carbon-14 5,370 years
uranium billion years

5. D. Half-life total time = 30 hours number of half-lives = 2
How much of a 20-g sample of sodium-24 would remain after decaying for 30 hours? Sodium-24 has a half-life of 15 hours.
GIVEN:
total time = 30 hours
t1/2 = 15 hours
original mass = 20 g
WORK:
number of half-lives = 2
20 g ÷ 2 = 10 g (1 half-life)
10 g ÷ 2 = 5 g (2 half-lives)
5 g of 24Na would remain.