Nuclear Chemistry Powerpoint 2003

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description

From Sir Paz

Transcript of Nuclear Chemistry Powerpoint 2003

Page 1: Nuclear Chemistry Powerpoint   2003
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Radioactivity – spontaneous emission of particles and or radiation

(proposed by Marie Curie)

•Three types of ray are produced by the decay, or breakdown, of radioactive

substances

A. Alpha rays ( α ) – consist of positively charged particles called alpha particles and therefore are

deflected by the positively charged plate.B. Beta rays ( β ) – or beta particles – are

electrons and deflected by negatively charged plateC. Gamma rays ( γ ) – have no charged and are

not affected by an external electric field or magnetic field

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Radioactive substance

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Radioactive substance

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Radioactive substance

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Radioactive substance

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Radioactive substance

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XAZ

Mass Number

Atomic NumberElement Symbol

Atomic number (Z) = number of protons in nucleus

Mass number (A) = number of protons + number of neutrons

= atomic number (Z) + number of neutrons

A

Z

1p11H1or

proton1n0

neutron0e-1

0-1or

electron0e+1

0+1or

positron4He2

42or

particle

1

1

1

0

0

-1

0

+1

4

2

23.1

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Balancing Nuclear Equations

1. Conserve mass number (A).

The sum of protons plus neutrons in the products must equal the sum of protons plus neutrons in the reactants.

1n0U23592 + Cs138

55 Rb9637

1n0+ + 2

235 + 1 = 138 + 96 + 2x1

2. Conserve atomic number (Z) or nuclear charge.

The sum of nuclear charges in the products must equal the sum of nuclear charges in the reactants.

1n0U23592 + Cs138

55 Rb9637

1n0+ + 2

92 + 0 = 55 + 37 + 2x023.1

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212Po decays by alpha emission. Write the balanced nuclear equation for the decay of 212Po.

4He242oralpha particle -

212Po 4He + AX84 2 Z

212 = 4 + A A = 208

84 = 2 + Z Z = 82

212Po 4He + 208Pb84 2 82

23.1

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23.1

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I. Nuclear Stability and Radioactive Decay

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n/p too large

beta decay

X

n/p too small

positron decay or electron capture

Y

23.2

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Predicting the mode of decay

1. High n/p ratio (too many neutrons; lie above band of stability) --- undergoes beta decay

2. Low n/p ratio (neutron poor; lie below band of stability) --- positron decay or electron capture

3. Heavy nuclides ( Z > 83) --- alpha decay

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II. Nuclear Transmutations

•Nuclear reactions that are induced in a way that nucleus is struck by a neutron or by another nucleus (nuclear bombardment) a.Positive ion bombardment

- alpha particle is the most commonly used positive ion- uses acceleratorsExamples:14

7 N + 42 He → 17

8 O + 11 H

94 Be + 4

2 He → 126 C + 1

0n

b.Neutron bombardment- neutron is bombarded to a nucleus to form a new nucleus- most commonly used in the transmutation to form

synthetic isotopes because neutron are neutral, they are not repelled by nucleus

Example: 58

26 Fe + 10 n → 59

26 Fe → 5927 Co + 0

-1 e

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Transuranium elements

-Element with atomic numbers above 92-Produced using artificial transmutations, either by:

a. alpha bombardmentb. neutron bombardmentc. bombardment from other nucleiExamples:

a.

b.

4He2Pu23994 + Cm242

961n0 +

1n0U23892 + U239

92

0 e-1Pu23994 + Np239

93 + 0-1 e

14N7U23892 + Es247

991n0+ 5c.

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III. Nuclear Energy

Recall:Nucleus is composed of proton and neutronThen, is the mass of an atom equal to the total mass of all the proton plus the total mass of all the neutron?

Example for a He atom:Total mass of the subatomic particles= mass of 2 p+ + mass of 2n0

= 2 ( 1.00728 amu ) + 2 (1.00867 amu)= 4.03190 amuAnd atomic weight of He-4 is 4.00150

Why does the mass differ if the atomic mass = number of protons + number of neutrons?

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Mass defect

-mass difference due to the release of energy-this mass can be calculated using Einstein’s equation E =mc2

2 11 H + 2 2

0 H → 42 He + energy

Therefore:-energy is released upon the formation of a nucleus from the constituent protons and neutrons-the nucleus is lower in energy than the component parts.-The energy released is a measure of the stability of the nucleus. Taking the reverse of the equation:

42 He + energy → 2 1

1 H + 2 20 n

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Therefore,-energy is released to break up the nucleus into its component parts. This is called the nuclear binding energy.-the higher the binding energy, the stable the nuclei.-isotopes with high binding energy and most stable are those in the mass range 50-60.

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Nuclear binding energy per nucleon vs Mass number

nuclear binding energynucleon

nuclear stability

23.2

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-The plot shows the use of nuclear reactions as source of energy.-energy is released in a process which goes from a higher energy state (less stable, low binding energy) to a low energy state (more stable, high binding energy).-Using the plot, there are two ways in which energy can be released in nuclear reactions:

a. Fission – splitting of a heavy nucleus into smaller nuclei

b. Fusion – combining of two light nuclei to form a heavier, more stable nucleus.

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Nuclear binding energy (BE) is the energy required to break up a nucleus into its component protons and neutrons.

BE + 19F 91p + 101n9 1 0

BE = 9 x (p mass) + 10 x (n mass) – 19F mass

E = mc2

BE (amu) = 9 x 1.007825 + 10 x 1.008665 – 18.9984

BE = 0.1587 amu 1 amu = 1.49 x 10-10 J

BE = 2.37 x 10-11J

binding energy per nucleon = binding energy

number of nucleons

= 2.37 x 10-11 J19 nucleons

= 1.25 x 10-12 J

23.2

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23.3

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Radiocarbon Dating

14N + 1n 14C + 1H7 160

14C 14N + 0 + 6 7 -1 t½ = 5730 years

Uranium-238 Dating

238U 206Pb + 8 4 + 6 092 -182 2 t½ = 4.51 x 109 years

23.3

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Nuclear Transmutation

Cyclotron Particle Accelerator

14N + 4 17O + 1p7 2 8 1

27Al + 4 30P + 1n13 2 15 0

14N + 1p 11C + 47 1 6 2

23.4

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Nuclear Transmutation

23.4

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Nuclear Fission

23.5

235U + 1n 90Sr + 143Xe + 31n + Energy92 54380 0

Energy = [mass 235U + mass n – (mass 90Sr + mass 143Xe + 3 x mass n )] x c2

Energy = 3.3 x 10-11J per 235U

= 2.0 x 1013 J per mole 235U

Combustion of 1 ton of coal = 5 x 107 J

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Nuclear Fission

23.5

235U + 1n 90Sr + 143Xe + 31n + Energy92 54380 0

Representative fission reaction

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Nuclear Fission

23.5

Nuclear chain reaction is a self-sustaining sequence of nuclear fission reactions.The minimum mass of fissionable material required to generate a self-sustaining nuclear chain reaction is the critical mass.

Non-critical

Critical

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Nuclear Fission

23.5

Schematic diagram of a

nuclear fission reactor

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Annual Waste Production

23.5

35,000 tons SO2

4.5 x 106 tons CO2

1,000 MW coal-firedpower plant

3.5 x 106

ft3 ash

1,000 MW nuclearpower plant

70 ft3 vitrified waste

Nuclear Fission

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23.5

Nuclear Fission

Hazards of the radioactivities in spent

fuel compared to uranium ore

From “Science, Society and America’s Nuclear Waste,” DOE/RW-0361 TG

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23.6

Nuclear Fusion

2H + 2H 3H + 1H1 1 1 1

Fusion Reaction Energy Released

2H + 3H 4He + 1n1 1 2 0

6Li + 2H 2 4He3 1 2

6.3 x 10-13 J

2.8 x 10-12 J

3.6 x 10-12 J

Tokamak magnetic plasma

confinement

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23.7

Radioisotopes in Medicine• 1 out of every 3 hospital patients will undergo a nuclear

medicine procedure

• 24Na, t½ = 14.8 hr, emitter, blood-flow tracer

• 131I, t½ = 14.8 hr, emitter, thyroid gland activity

• 123I, t½ = 13.3 hr, ray emitter, brain imaging

• 18F, t½ = 1.8 hr, emitter, positron emission tomography

• 99mTc, t½ = 6 hr, ray emitter, imaging agent

Brain images with 123I-labeled compound

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Geiger-Müller Counter

23.7

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23.8

Biological Effects of RadiationRadiation absorbed dose (rad)

1 rad = 1 x 10-5 J/g of material

Roentgen equivalent for man (rem)

1 rem = 1 rad x Q Quality Factor-ray = 1

= 1 = 20

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Chemistry In Action: Food Irradiation

Dosage Effect

Up to 100 kiloradInhibits sprouting of potatoes, onions, garlics. Inactivates trichinae in pork. Kills or prevents insects from reproducing in grains, fruits, and vegetables.

100 – 1000 kilorads Delays spoilage of meat poultry and fish. Reduces salmonella. Extends shelf life of some fruit.

1000 to 10,000 kiloradsSterilizes meat, poultry and fish. Kills insects and microorganisms in spices and seasoning.