1

Nuclear Chemistry

Proposal: build a

nuclear power plant

in Broome County.

List the pros & cons

2

Nuclear Chemistry

Friend or Fiend

3

The NucleusWhat is in the nucleus?

How big is it vs. the atom?

How was it discovered?

4

Isotope Notation(protons & neutrons in nucleus)

X(p+n)

p C14

6

mass #

atomic #

C -14X -(p+n)

5

Notation: Try It

U238

92

Pb -210

How many p, n, and e- ?

What is the nuclear charge of Br?

What is the charge of the

bromide ion?

6

Types of Radiation

Unstable nuclei will change

(or “decay”) by emitting radiation.

b

g

a

+

-unstable

nucleielectric

fieldscreen

7

a Radiation

Some nuclei eject a positive

a (alpha) particle. A piece of

paper can stop an a particle.

Why is it stopped so easily?

2a4

high mass

high charge

What element is a related to?

8

b Radiation

Some nuclei eject a fast

moving electron or beta particle

(b particle).

e-

9

g Radiation

g (gamma) radiation is high energy

light (electromagnetic radiation)

that can easily penetrate wood,

bricks, and human tissue.

g

10

Radiation Damage

Type of

Radiation

Damage to

Human Tissue

a low

b moderate

g high

11

Elementary Particles

1Proton 1p or 1H

1

44Alpha 2He or 2a

00Positron 1e or 1b or b+

0 0Electron -1e or -1b or b-

1Neutron 0n

0Gamma 0g

12

Electron vs. Beta (Identical)

-1e or -1b or b-

From atomic orbit

Ejected from nucleus

00

13

1.Mass number of products &

reactants are equal.

(superscripts balance)

2.Charge of products & reactants

are equal (subscripts balance)

Balancing Nuclear Reactions

14

Balancing Nuclear Reactions

137

55Cs

137

56Ba + X

212

84Po

208

82Pb + X

15

Balancing Nuclear Reactions

78

33As

-1e + X0

14

7N + 0n

14

6C + X

1

16

Try Another!

Write a balanced nuclear

equation for the decay of

Ra-226 to produce an isotope

of radon (Rn) and an alpha

particle.

17

Transmutation

1. Natural Transmutation

2. Artificial Transmutation

(man-made)

Conversion of one

element into another

(Dalton was wrong!)

18

A

Natural TransmutationAn unstable nucleus changes

into another element by emitting

a particle in a process called

“radioactive decay.”

Bparticle and/or

g radiation (light)

19

What Holds a

Nucleus Together?

charge

repulsion of

protons

nucleus fly

apart

“strong

force”

holds nucleus

together

vs

20

Nuclear Stability

Over 1500 isotopes (nuclei) are

known, but only 264 are “stable.”

21

Belt of Stability

20 40 60 80

40 80 120

#p = #n

Number of p

Nu

mb

er

of

n

22

Stable Nuclei

1.Low atomic number: #n = #p

e.g. C-12, N-14, O-16

2.High atomic number: #n > #p

e.g. Pb-206 (82 p & 124 n)

3.All nuclei with atomic

number > 82 are unstable

(too many p & n)

n

p

23

Belt of Stability

20 40 60 80

40 80 120

Number of p

Nu

mb

er

of

n Isotope mass

> atomic mass

AIsotope mass

< atomic mass

Bb-

emission

b+emission

C > Pb

a emission

Periodic Table

is a guide

to stability

24

Region A

0n 1p1 1

42

19K

42

20Ca + -1e

0

0-1e+ b-

emission

Isotope mass greater than atomic

mass on P.T. results in b- emission

greater than P.T. (39 amu)

25

Region B

111p 0n + 1e

0

37

19K

37

18Ar + 1e

0

Isotope mass less than atomic

mass on P.T. results in b+ emission

b+

emission

less than P.T. (39 amu)

26

Region C

For nuclei past lead (Pb) alpha

emission reduces both n & p.

238

92U

234

90Th + 2a

4

Past Pb on P.T.

27

Nuclear Stability: Summary

Region Emission

Atomic

numbers

1-82

A: too many n

mass # > ave. mass

beta

b-

B: too few n

mass # < ave. mass

positron

b+

Atomic

number

>82

C: too many p & n

alpha

a

28

Using Table N

Write balanced equations for

the decay of:

N-16

Rn-222

Table N shows the natural

transmutation of several “nuclides.”

29

Predict the Reaction

Write the decay reaction of:

Cu-66 Ti-45

Pu-239 C-14

Check Table N first.

If not on ‘N’, use “rules of stability.”

30

Radioactive Decay Series

Sequence of nuclear reactions

leading to stable isotope.

31

Radioactive Decay Series

parent daughter

Final stable daughter: Pb206

82

e.g.

238

92U

234

90Th + 2a

4

Still not stable

32

Radioactive Half-Life

Half-life (T½): time for one-half

of the radioactive atoms to

decay into products.

Long T½ stable isotope

33

Half-Life Decay

0 1 2 3 half-lives

100

50

25

0%re

ma

inin

ginitial

1 half-life

2 half-lives

3 half-lives

34

Solving Half-Life Problems

Elapsed time divided by half-life is

the number of half-life periods.

Example: If half-life is 7.2 s and

28.8 s have gone by, then:

= 4 half-life periods28.8 s

7.2 s

For each half life period, only ½

of the starting isotopes remain.

Half-Life: Loop Method

35

How much of a 50.g sample of

K-42 remains after 37.2 h?

Table N shows half-life is 12.4 h.37.2 h

12.4 h= 3 half-life periods

(3 loops)50. g

6.25 g remains.

1half-life

25 g

2half-life

12.5 g

3half-life

6.25 g

36

Half-Life Problem

You start with 68 g of C-14

•Write a balanced equation

for its decay.

•How long is 3 half-life periods?

•How many grams of C-14

remain after 17,200 yr?

37

Half-Life Problem

What percent of I-131will

remain after 40.1 days?

What fraction of I-131will

remain after 24 days?

38

Half-Life Problem

87.5% of an isotope

decays in 4.8 days.

What is its half-life?

Careful !

39

Alchemist’s Dream

40

Artificial

Transmutation

The man-made conversion of

one element into another element.

41

Artificial Transmutation

“Bombard” a nucleus with a

particle to form a heavier element.

2 reactants

= artificial trans.

14

7N + 0n

14

6C + 1p

1 1

can’t predict

both products

neutron injected

into nucleus

42

Artificial Transmutation

Rutherford 1919:

discovered the proton

a injected by

particle accelerator

14

7N + 2a

17

8O + 1p

4 1

43

Artificial Transmutation

Chadwick 1932:

discovered the neutron:

Why was detecting the

neutron so difficult?

9

4Be + 2a

12

6C + 0n

4 1

44

Artificial TransmutationAll elements with Z > 92

(transuranium elements) were

produced by transmutation.

Artificial or man-made

238

92U + 0n

239

93Np + -1e

1 0

45

Uses of RadioisotopesRadioactive dating

Radioactive tracers (read p.860)

Medical applications

Nuclear power

46

Radioactive Dating: C-14

C-12 >99% stable

C-14 <1% unstable

After the plant dies,

only C-14 decays.

The ratio of C-14 to C-12

can tell the age since death.

47

Radioactive Dating

Dates living things up to ~40,000 yr

14

6C

14

7N + -1b T½ = 5715 yr

0

Dates rocks billions of years.

238

92U

206

82Pb + 6 -1b + 8 2a

T½ = 4.47 x 109 yr

40

Does this equation balance?

48

Radioactive Dating

49

Cobalt-60, a gamma ray

emitter for treating cancer.

Tc-99 for treatment of cancer.

Medical

Applications

Iodine-131 for treatment of

thyroid cancer.

(injested, so need short T½)

50

Nuclear Power

Fission- splitting heavy nuclei

Fusion- combining

light nuclei

51

Fission & FusionMass of products is less

than mass of reactants.

Mass is lost!!!

energy

produced

missing

mass

speed of

light

3 x 108m/s

E = mc2

52

Nuclear Fission

Used in nuclear

power plants

Splitting a large nucleus

into smaller isotopes,

releasing energy.

53

Nuclear Power PlantU-235, hit by a neutron, splits

into smaller nuclei &

3 neutrons & energy.

“chain reaction”

235

92U+ 0n

90

38Sr+ Xe+3 0n

143

5411

Show this reaction balances.

54

Nuclear Fusion

Small nuclei combine (unite)

to form a larger nucleus and

release energy.

Energy from the sun is

produced by fusion.

Required very high temps.

(40,000,000oC) Why?

55

Solar Fusion

E = mc2

1

1H + 2 -1e

4

2He + energy4 0

Hydrogen nuclei fuse into helium.

56

Detecting Radiation

Your senses cannot detect

radiation.

Geiger counter- b radiation

Scintillation counter- all

types of radiation

Film badge-all types of radiation

57

Reactions:Chemical NuclearAtoms

rearranged

Elements

changed

Involves

electrons

Involves all

atomic particles

Small DE Large DE

Rate depends

on T, P, etc.

Rate is constant

58

Warm-up

59

•What are the three types of

radiation (names and symbols).

• Which is most and least

damaging radiation to humans?

•How many p+, n, e- in Es-252

Warm-up

60

Write a balanced equations for

the radioactive decay:

Neon-19

Bromine-81

Neptunium-237

Warm-up

61

Write an equation for the decay of:

technetium-99

silicon-26

californium-252

Use Table N or

compare mass number

vs. atomic mass.

Warm-up

62

Write an equation for the decay of

O-19, with a half-life of 29 s.

If you start with 120 g of O-19, how

much remains after 116 s?

How long will it take for a sample of

O-19 to drop to one-eighth of its

original amount?

Warm-up

63

If aluminum-27 is bombarded

with an alpha particle, one of the

products is silicon-30.

•What is this process called?

•Write a balanced equation.

14.0 g of Co-60 remains after 21 yr.

What was the original sample size?

Write an equation for the decay of

Fe-53. What is this process called?