1 Nuclear Chemistry 2 The stability of the atom The vast majority of all atoms are incredibly stable and their nucleus never changes. However, a small.

1

Nuclear ChemistryNuclear Chemistry

2

The stability of the atom

• The vast majority of all atoms are incredibly stable and their nucleus never changes.

• However, a small percentage of atoms will have their nucleus break apart and give off radiation.

• This breaking apart is called decay.

• Decay can happen naturally or we can force it to happen through nuclear reactions.

3

RadioactivityRadioactivity

• One of the pieces of evidence for the One of the pieces of evidence for the fact that atoms are made of smaller fact that atoms are made of smaller particles came from the work ofparticles came from the work of

Marie Curie Marie Curie (1876-1934).(1876-1934). • She discoveredShe discovered radioactivityradioactivity, ,

the spontaneous disintegration of the spontaneous disintegration of some elements into smaller pieces.some elements into smaller pieces.

4

Radioactive Decay• Most of the isotopes which occur naturally are

stable.

• Some unstable isotopes are said to be radioactive.

– Radioactive (unstable) isotopes are called radioisotopes

• Radioisotopes eventually decay and change into more stable forms. The stable form is a different element. This process is called transmutation.

5

• Often times, when a radioisotope decays and becomes stable it will release a particle and change into a different element.

• Some radioisotopes release energy by emitting radiation during the process of decay.

6

Examples of radioactive isotopes

7

Radioactive decay results in the emission of either:

• an alpha particle (); a positively charged helium isotope; contains two neutrons and two protons

•a beta particle (); a high speed electron•or a gamma rayElectromagnetic radiation;; pure energy; called a ray rather than a particle

Radioactive Decay

8

Examples of radioactive decay

C-14 N-14 + beta particle

P-32 S-32 + beta particle

I-131 Xe-131 + beta particle

U-238 Th-234 + alpha particle

9

Penetrating AbilityPenetrating Ability

10

11

Half-LifeHalf-Life

• Chemists are interested in the amount of time Chemists are interested in the amount of time it takes for elements to decay into another it takes for elements to decay into another element. They use the term “half-life” to element. They use the term “half-life” to measure the time it takes an element to decay. measure the time it takes an element to decay.

•HALF-LIFEHALF-LIFE is the time that it takes for 1/2 is the time that it takes for 1/2 a sample to decompose.a sample to decompose.

12

Examples of half life

• Lead-210 has a half life of 22 years.

• If you start with 80 g of Pb-210….

After 22 years, you’ll have 40 g of Pb-210

After 44 years, you’ll have 20 g of Pb-210

After 66 years, you’ll have 10 g of Pb-210

After 88 years, you’ll have ______ of Pb-210

13

• Po-218 has a half-life of 3 minutes

If you start with a sample of 100 g of Po-218

How much is left after 1 half life? ___

How much is left after 2 half lives?____

How much is left after 4 half lives? ____

14

Half-LifeHalf-Life

Decay of 20.0 mg of Decay of 20.0 mg of 1515O. What remains after 3 half-lives? O. What remains after 3 half-lives? After 5 half-lives?After 5 half-lives?

What is the half-life?

15

1) What is the half-life?2) How long is 3 half-lives? How much is

left?

16

If we start with 200 atoms of a radioactive substance, how many would remain after one halflife?_________ after two half-lives? _________ after three half-lives? ___________ after four halflives?__________

17

1) What is the half life?

2) How long for 3 half lives?

18

Forcing the atom to split up

• Fission- A reaction in which an atomic nucleus of a radioactive element splits by bombardment from an external source, with simultaneous release of large amounts of energy, used for electric power generation.

19

Nuclear FissionNuclear FissionFission is the splitting of atomsFission is the splitting of atoms

These are usually very large atoms, that they are not very

stable.

20

21Nuclear Fission & Nuclear Fission & POWERPOWER

• Currently about 103 Currently about 103

nuclear power plants in nuclear power plants in

the U.S. and about 435 the U.S. and about 435

worldwide.worldwide.

• 17% of the world’s 17% of the world’s

energy comes from energy comes from

nuclear.nuclear.

22Figure 19.6: Diagram of a nuclear power plant.

23

Nuclear Fusion The opposite of Fission

Fusion small nuclei combine

2H + 3H 4He + 1n +

1 1 2 0

Occurs in the sun and other stars; has ne

Energy

24Fusion

• Excessive heat can not be contained

• Attempts at “cold” fusion have FAILED.

• “Hot” fusion is difficult to contain

25

Draw a Double Bubble Map of Fusion and Fission

fusion fission

Differences Similarities DifferencesDifferences Similarities Differences

26

• http://www.hamilton-local.k12.oh.us/Downloads/9-29_Half%20Life%20Worksheet.pdf

27Kinetics of Radioactive Kinetics of Radioactive DecayDecay

For each duration (half-life), one half of the substance

decomposes.

For example: Ra-234 has a half-life of 3.6 days

If you start with 50 grams of Ra-234

After 3.6 days > 25 gramsAfter 3.6 days > 25 grams

After 7.2 days > 12.5 gramsAfter 7.2 days > 12.5 grams

After 10.8 days > 6.25 gramsAfter 10.8 days > 6.25 grams

28

Learning Check!

The half life of I-123 is 13 hr. How much of a 64 mg sample of I-123 is left after 39 hours?

29

Effects of RadiationEffects of Radiation

30

Geiger Counter

• Used to detect radioactive substances

31

32

Radiocarbon DatingRadiocarbon DatingRadioactive C-14 is formed in the upper atmosphere Radioactive C-14 is formed in the upper atmosphere

by nuclear reactions initiated by neutrons in cosmic by nuclear reactions initiated by neutrons in cosmic radiationradiation

1414N + N + 11oon ---> n ---> 1414C + C + 11HH

The C-14 is oxidized to COThe C-14 is oxidized to CO22, which circulates through , which circulates through

the biosphere.the biosphere.

When a plant dies, the C-14 is not replenished.When a plant dies, the C-14 is not replenished.

But the C-14 continues to decay with tBut the C-14 continues to decay with t1/21/2 = 5730 years. = 5730 years.

Activity of a sample can be used to date the sample.Activity of a sample can be used to date the sample.

33Nuclear Medicine: Nuclear Medicine: ImagingImaging

Thyroid imaging using Tc-99mThyroid imaging using Tc-99m

34

Food Food IrradiationIrradiation

•Food can be irradiated with Food can be irradiated with rays from rays from 6060Co or Co or 137137Cs.Cs.•Irradiated milk has a shelf life of 3 mo. Irradiated milk has a shelf life of 3 mo.

without refrigeration.without refrigeration.•USDA has approved irradiation of meats USDA has approved irradiation of meats

and eggs.and eggs.