Nuclear ChemistryNuclear Chemistry

Bravo – 15,000 kilotons

Nuclear SymbolsNuclear Symbols

23592U

Element symbol

Mass number (p+ + no)

Atomic number(number of p+)

Types of Radioactive DecayTypes of Radioactive Decay

alpha production (): helium nucleus

beta production (): neutron splits into an electron and a proton

92238

24

90234U He Th

90234

91234

10Th Pa e

2+

CREATING A REACTION CREATING A REACTION ((αα-particle)-particle)

• On either side of the arrow, the mass number and atomic number MUST be the same (alpha-particle is always a helium nucleus)

238U 4He + 234Th

92 2 90

• On the left side, mass number is 238– On the right side, 234 + 4 = 238

• On the left side, the atomic number is 92– On the right side, 90 +2 = 92

CREATING A REACTION CREATING A REACTION ((ββ-particle)-particle)

• Both sides of the reaction still need to balance.– In beta-radiation, a neutron splits apart to

form an electron and a proton

234Th + 234Pa 0e 90 91 -1

• On the left side, mass number is 234– On the right side, 234 + 0 = 234

• On the left side, the atomic number is 90– On the right side, 91 - 1 = 90

Alpha Alpha RadiationRadiation

Limited to VERY large nucleii.

Beta Beta RadiatioRadiatio

nn

Converts a neutron into a proton.

PRACTICEPRACTICE

• Each of the following compounds emits an alpha particle, write the balanced nuclear reaction

• 222Ra 88

• 208Po 84

PRACTICEPRACTICE

• Each of the following compounds emits a beta particle, write the balanced nuclear reaction

• 14C 6

• 131I 53

Types of Radioactive DecayTypes of Radioactive Decay

gamma ray production ():

positron production:

electron capture: (inner-orbital electron is captured by the nucleus)

92238

24

90234

002U He Th

1122

10

1022Na e Ne

80201

10

79201

00Hg e Au

GAMMA RADIATIONGAMMA RADIATION

• Gamma radiation does not produce any particles by itself– It is tied to another radioactive decay– Because the release of radioactive

particles “frees” some energy in the nucleus, this energy takes the form of gamma radiation•There is a lot of energy holding the nucleus together so gamma radiation has a LOT of energy

Positron and Electron Positron and Electron capturecapture

• Positron emissions occur when a proton splits apart into a neutron and an electron– Therefore the mass number does not

change, but the atomic number changes the element into something new

• Electron capture occurs when a proton “captures” one of the inner valence electrons and converts it into a neutron– This causes the release of a powerful

neutrino (as powerful as gamma radiation)

TRY THESETRY THESE

• The following go through a positron emission. Write the balanced reaction:

• 17F 9

• 31S 16

TRY THESETRY THESE

• The following go through an electron capture. Write a balanced equation.

• 76Kr 36

• 125I 53

ANOTHER WAY TO ANOTHER WAY TO SYMBOLIZE ISOTOPESSYMBOLIZE ISOTOPES

• So far we have seen one way to symbolize isotopes: 17F

9

31S 16

• Since we know the number of protons, we can symbolize the isotope with just the mass number:• Fluorine-17• Sulphur-31

Types of RadiationTypes of Radiation

Deflection of Decay ParticlesDeflection of Decay Particles

Opposite charges_________ each other.

Like charges_________ each other.

attractrepel

NuclearNuclearStabilityStability

Decay will occur in such a way as to return a nucleus to the band (line) of stability.

HALF LIFEHALF LIFE

• When an isotope goes through a radioactive emission, it does so at a fairly constant rate

• Scientists use this property to date items

• Half-life: The time it takes for ½ of a radioactive isotope to decay to a stable form– Example: Carbon-14 has a half life of 5730 years– It takes 5730 years for ½ of radioactive Carbon-14

to decay to the stable form or Nitrogen-14

–14C 0e + 14N 6 -1 7

Half-life ConceptHalf-life Concept

HOW TO SOLVE HALF-LIFEHOW TO SOLVE HALF-LIFE

• Iodine-131 is used to destroy thyroid tissue in an over-productive thyroid gland. The half-life of iodine-131 is 8 days. If a hospital received a shipment of 200g of iodine-131, how much iodine-131 would remain after 32 days?

SOLUTIONSOLUTION

• Step 1: Find out how many ½-lives have occurred– (32 days/8 days for half-lives)– 4 half-lives

• Step 2: Four each half-life, divide the sample by 2– 4 half lives = ½ x ½ x ½ x ½ = 1/16

• Step 3: Divide the initial sample size– 200g/16 = 12.5g will remain

TRY THISTRY THIS

• Mercury-197 is used for kidney scans and has a half-life of 3 days. If the 32g of mercury-197 is ordered, but takes 15 days to arrive, how much would arrive with the shipment?

Sample Half-LivesSample Half-Lives

A A Decay Decay SeriesSeries

A radioactive nucleus reaches a stable A radioactive nucleus reaches a stable state by a series of stepsstate by a series of steps

Nuclear Fission and FusionNuclear Fission and Fusion

•Fusion: Combining two light nuclei to form a heavier, more stable nucleus.

•Fission: Splitting a heavy nucleus into two nuclei with smaller mass numbers.0

192

23556

1423691

013n U Ba Kr n

23

11

24

10He H He e

Energy and MassEnergy and MassNuclear changes occur with small but measurable losses of mass. The lost mass is called the mass defect, and is converted to energy according to Einstein’s equation:

E = mc2

m = mass defectE = change in energy

c = speed of light

Because c2 is so large, even small amounts of mass are converted to enormous amount of energy.

FissionFission

Fission ProcessesFission Processes

Event

NeutronsCausingFission Result

subcritical < 1 reaction stopscritical = 1 sustained reactionsupercritical > 1 violent explosion

A self-sustaining fission process is A self-sustaining fission process is called a chain reaction.called a chain reaction.

A Fission ReactorA Fission Reactor

FusionFusion

MORE PRACTICE PROBLEMSMORE PRACTICE PROBLEMS

• Nitrogen-13 emits beta radiation and decays to Carbon-13. This has a half-life of 10 minutes. You start with 2.0g of Nitrogen-13:– Write out the balanced nuclear

reaction.– Calculate how much nitrogen-13

is remaining after 40 minutes.

MORE PRACTICE PROBLEMSMORE PRACTICE PROBLEMS

• Manganese-56 decays with beta radiation and has a half-life of 2.6 hours. You begin with 1mg of Manganese-56:– Write the balanced nuclear

reaction.– How much manganese-56 is

left after 10.4 hours?