Ch. 26 Nuclear Chemistry

Ordinary Chemical Rxns

No new _______ can be produced

Only the e- participate

Relatively small amounts of energy are _______ or _______

Rate of rxn depends on _______ such as concentration, temperature, catalysts, and pressure.

Elements may be converted from one _______ to _______ .

Particles _______ the nucleus are involved.

Tremendous amounts of energy are _______ or _______

Rate of rxn is not influenced by _______ factors

vs. Nuclear Rxns

Several types of radioactive decay Nuclear particles

Nuclide too large – ____ or

Too many neutrons _______ (electron) or

Too many protons, _______ (also called a positron or electron capture) or

He42 42

01- e01-

01 e01

4

Other types of particles used during radioactive decay

Neutron

Proton or

Gamma (high energy including x-rays) heavy proton

n10

p11 H1

1

00

H21

Balancing Nuclear Rxns For the general reaction

The two conservation principles demandA1 = A2 + A3

andZ1 = Z2 + Z3

◦A's are atomic mass numbers ◦Z's are atomic numbers

YRQ 3

3

2

2

1

1

AZ

AZ

AZ

Beta EmissionA beta particle is an electron _______ from

the nucleus when a neutron is converted to a proton.

β emission = electron 1n = 1p + -1β

228Ra -1β + 228Ac

14C 14N + -1β

Positron emission or electron capture (___________)

+1β = positron

1p 1n + +1β

38K 38Ar + +1β

15O 15N + +1β

K capture106Ag + -1e 106Pd 37Ar + -1e 37Cl

Alpha emissionAlpha emission 4α or 4He204Pb 200 Hg + 4α

All nuclides with atomic # greater than ___ are radioactive. Most decay by _______ emission

*only stable nuclide with atomic # 83 is 209Bi

Types of Nuclear Rxns

83+ protons alpha decay

neutron rich β emission

neutron poor K capture or positron emission

Radiation Interaction with Matter

History1896 - _______ _______ –discovers

radioactivity in U salts

1898 - _______ and _______ Curie –discover two new radioactive elements, Po and Ra

1898 - _______ _________ –discovers that radioactivity has two forms: α and β radiation

Belt of stability

~ _______ have a stabilizing effect on proton – proton _______

~ neutrons and protons swap particles called _______ which keeps the atom together

~ as # of protons increases, atoms need even _______ neutrons.

Mass deficiency Δm – Δm – for a nucleus is the difference

between the sum of the _______ of e-, p+ and no in the atom and the _______ measured _______ of the atom.

Table 26-1 Δm = (sum of all e-, p+ and no) – (actual

mass of the atom)

1 amu = 1.661 x 10-24 grams

Example ProblemEx. 1) Calculate the mass deficiency for 39K

in amu/atom and in g/mol. The actual mass of 39K is 39.32197 amu per atom

Nuclear binding energy

(BE) provides the powerful short-range force that holds the nuclear particles together in a small volume.

_______ Einsteins E = mc2

Ex. 2) Use the value for Δm 39 K to calculate the nuclear binding energy in J/mol of K atoms. 1J = 1kg m2/s2.

Fission and Fusion

Both processes generate large amounts of energy

Nuclear fission

◦splitting of a heavy nucleus into two lighter nuclei

Nuclear fusion

◦combining two light nuclei into one heavier nucleus

Fusion(fuse – put together) _______ nuclei into _______

ones.

Extremely high energies or temperatures are necessary to initiate fusion reactions.Ex. Stellar energy source is fusion (stars)

~ still a mass loss E = mc2

~ fusion typically uses H as a fuel 1H ~ Hydrogen (protium) 2H ~ Heavy H (deuterium) 3H ~ tritium

2H + 2H 3H + 1H

Fusion _______ – Why?~ no chance of _______ _______ ; no

radioactive products; Hydrogen is easy to get (75% of universe is Hydrogen); _______ ; and fusion produces _______ energy per amu.

Bad – Why? ~ _______extreme heat and harder to do.

Fissionoccurs when _______ nuclei break down into

_______ ones. Ex. U, Th, Pa, Pu,

Some fission rxns are spontaneous while others require activation by neutron bombardment

Very _______ – chain reaction - mass goes down and energy is produced.

Controlled at Nuclear Power Plants pg 1027. ~ know the different parts◦Reactors, Fuel, Moderator, Control Rods, Cooling Systems,

and Shielding

Pressurizes water reactor Boling water reactorPWR ~ 2000 psi BWR ~ 1000 psi

Nuclear Power Plant accidents–Three Mile Island, PA (_______ ) Nuclear

reactor malfunctioned – no meltdown, but some radioactive contamination. Affected a 25 mile radius

–Chernobyl , Russia (_______ ) Nuclear reactor’s cooling system failed – meltdown. Released thirty times the radioactivity of the atomic bombs dropped on Hiroshima and Nagasaki. 31 lives were lost immediately. Radiation in soil & atmosphere still presents significant health risks.

One of the main concerns: Acute radiation to cells causes them to divide and grow without control – this creates a tumor (cancer) *More harmful to children than adults

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◦Japan (_______ ) After the earthquake and tsunami that hit Japan in 2011. The cooling system of the nuclear power plant in Fukushima failed causing the reaction to spiral out of control. The heat produced by the reaction caused the Uranium to decay to Cesium 137, a very unstable atom that caused most of the environment to become radioactive. This has caused the area to become a dead zone.

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Fusion

Merge (makes heavier products)

Release tremendous amounts of energy

Produces no radioactive waste

Hydrogen + Hydrogen Helium

Involves changes in the atom at the subatomic level

Currently not feasible

Fission

Split up (makes lighter products)

Release tremendous amounts of energy

Produces radioactive waste

Uranium lots of smaller radioactive elements

Involves changes in the atom at the subatomic level

Used at nuclear reactors

Benefits of Nuclear RadiationRadiation & radioactive materials can be used in a number of ways. The following merely touches on the subject:

Agriculture - The increase in the volume and quality of grains & cereals has been vastly improved by growing superior strains labeled with radioactive isotopes.  These improvements are helping to alleviate famine in third world countries.

Cancer Treatments - Cancerous cells can be selectively killed by the use of radioactivity, either in the form of directed beams, as for breast cancer, or as radioactive bullets that are designed to migrate directly to the cancerous cells that need killing. Chemotherapy, one of the only current alternatives, which involves the use of invasive drugs, but it is very difficult for the patient.

Environmental Measurements - The movement of pollutants through the environment (ex. ground water and rivers)- can be accurately measured by the use of radioactive tracers.

Food - Food, such as beef and chicken, that has been sterilized by irradiation(the process of being exposed to radiation) has a longer shelf life and is free of E. coli ~ a bacterium that can kill as a result of eating poorly cooked food. (children are more susceptible to E. coli than adults)An extension of food irradiation could save the lives of

many children and would be particularly useful in developing countries where refrigeration is not available.

Generation of Electricity - Over 440 nuclear plants around the world contribute some 16% of the world's electrical energy needs.  109 plants in the U.S. contributed 22% of the US's consumption of electricity in 2000.

Medical Diagnostics - The use of radiation in the medical world extends from X-rays, through magnetic resonance imaging (MRI), to the use of radioactive tracers to diagnose such varied conditions as faulty thyroid glands or bone problems.  The use of radioactive tracers often replaces the use of invasive surgical diagnosis.

Polymerization of Plastics - Plastics can be polymerized by radiation instead of damaging heat treatments.  The polymerized plastics are used in such applications as car dashboards, which would, otherwise, crack badly under heat in the summer.

Quality Control of Metal Parts - The integrity of metal parts such as aircraft engine blades can be verified by radiophotography on a conveyor belt instead of having to destroy a sampling of blades to ensure they are intact.

Research in Biology - The use of radioactive tracers allows the non-invasive tracking of elements and drugs through the body for both metabolic studies and medicine.

Space Power - When small amounts of power are needed in space in regions where solar power is inefficient (on the dark side of the moon or when large solar panels are impossible), plutonium batteries are ideal producers of compact energy.

Radioactive Half-lives and Decay____________ turn into other elements

the closer they are to the Belt of stability, the _______ it takes

every single nuclide has a different rate of decay, we measure the different rates of decay with half-life.

Half-life: the time it takes for _______ of the nuclei to _______ into something else.

Radioactive Dating______________ can be used to estimate the ages of items of

organic origin.

14C is produced continuously in the upper atmosphere by the bombardment of 14N by cosmic-ray neutrons:

14C atoms react with O2 to form CO2

◦CO2 then is incorporated into plant life by photosynthesis.

After material dies 14C content decreases from radioactive decay◦ 14C half-life is 5730 years.

p C n N 11

146

10

14

01-147

146 N C

The uranium-lead and potassium-argon methods are used for dating older objects.Uranium-lead is one of the oldest and

most refined of the radiometric dating schemes, with a dating range of about 1 million years to over 4.5 billion years. ◦The method relies on two separate decay

chains, the Uranium series, from 238U to 206Pb, with a half-life of 4.47 billion years and the actinium series from 235U to 207Pb, with a half-life of 704 million years. These decay routes occur via a series of alpha (and beta) decays.

Potassium-Argon dating is a viable technique for dating very old archaeological materials. Geologists use this method to date rocks as much as 4 billion years old. It is based on the fact that some of the radioactive isotope of Potassium, K-40, decays to the gas Argon as Ar-40.   

Potassium is one of the most abundant elements in the Earth's crust, 2.4% by mass. One out of every 10,000 Potassium atoms is radioactive Potassium-40. These each have 19 protons and 21 neutrons in their nucleus. If one of these protons is hit by a beta particle, it can be converted into a neutron. With 18 protons and 22 neutrons, the atom has become Argon-40, an inert gas.

y103.1t

Ar K 9

01-

4018

4019

21

e

Half-life equations

t1/2 = half-lifek = decay constanta = 1, a is always 1 for radioactive decayAo = initial activity t = timeA = activity (disintegrations per gram)

t1/2 = 0.693 k = 0.693 ak at1/2

ln Ao = akt or lnA = -akt A Ao

Ao = e^akt or A = e^-akt

A Ao

Example ProblemsEx. 3) What is k for 60Co? How much 60Co

remains 15.0 years after it is initially made? 60Co has a half-life of 5.27 years.

Ex. 4) Estimate the age of an object whose 14C activity is only 55% that of living wood. The half-live of carbon-14 is 5730 years.

Detection of RadiationDetection methods available depend on the fact that particles

and radiations emitted by radioactive decay are energetic and some carry charges

______________ Radioactivity affects photographic plates or film as does ordinary light.

______________ contain air saturated with a vapor, the particles emitted in radioactive decay ionize air molecules in the chamber and then the vapor subsequently condenses on these ions. Photographing the ion tracks can let you study their nature in detail

Gas Ionization Counters Ex. Geiger-Mueller counter

ions produced by ionizing radiation passing between high voltage electrodes cause a current to flow between the electrodes and then the current is amplified.

Fluorescence Detection Ex. Scintillation counter

Fluorescent substances absorb energy from high energy rays and then emit the energy through visible light.

Radiation all around usNaturally occurring _______

◦K-40, Thorium, Radium◦Cosmic

Radiation in _______ products◦Fiestaware

(1936 – 1959) used U (1959 – 1973) used depleted U

◦Fire DetectorsUses Americium-95

◦Antique Clocks and watchesUsed Radium which glows in the dark1917 – women who worked at the U.S. Radium Factory were told that the Ra was harmless. They ingested deadly amounts of Ra and in turn became incredibly ill. This is an important time in history for labor rights

Extra problems

1) Stars are enormous thermonuclear fusion reactors generating enormous amounts of heat and energy. What keeps stars from blowing themselves apart and how do they remain stable for millions and billions of years?

2) How are thermonuclear reactors designed so that the hot plasma that’s around 10 million degrees does not touch the sides of the reactor and melt it?