Atomic Structure

What does the atom look like???

Early Models of the Atom

• Democritus: c. 470-400 BC Greek Philosopher– matter is composed of tiny, discrete, indivisible

particles called atomos (Greek word meaning indivisible).

– Ideas based on philosophical speculation– Theory not accepted due to influence of

Aristotle

• An atom is the smallest part of an element that retains the chemical properties of thatelement. It cannot be broken down by ordinary means.

Antoine Laurent Lavoisier: A.D. 1780

• Law of Conservation of Matter states that matter is neither created nor destroyed, it only changes form.– 1st to announce that air was

made up of 2 gases – oxygen and azote (nitrogen)

– Work done on combustion, oxidation, and gases• Lavoisier is known as the Father

of Chemistry.

• In 1771, at age 28, Lavoisier married the 13-year-old Marie-Anne Pierrette Paulze.

• Over time, she proved to be a scientific colleague to her husband.

• She translated documents and chemistry books from English.

• She created many sketches and carved engravings of the laboratory instruments he used.

• She also edited and published Lavoisier’s memoirs after his death.

• She hosted parties at which eminent scientists discussed ideas and problems related to chemistry.

Lavoisier was Guillotined May 8, 1794

• An appeal to spare his life so that he could continue his experiments was cut short by a judge saying: "The Republic needs neither scientists nor chemists; the course of justice cannot be delayed.”

• One and a half years following his death, Lavoisier was exonerated by the French government.

• When his private belongings were delivered to his widow, a brief note was included reading "To the widow of Lavoisier, who was falsely convicted."

Joseph Louis Proust: A.D. 1799

• Law of Definite Proportion states that compounds always have the same elements in the same

proportion by mass. Ex) the ratio of H:O in water is always 2:16.

John Dalton A.D.1766-1844

• English schoolteacher• Some of the original chemical symbols from his book:

John Dalton: A.D. 1803-1808

Proposed Atomic Theory of Matter:

1. An element is composed of extremely small, indivisible particles called atoms

2. All atoms of a given element have identical properties that differ from those of other elements

3. Atoms cannot be created, destroyed, or transformed into atoms of other elements

Dalton’s Atomic Theory (cont.)

4. Compounds are formed when atoms of different elements combine with one another in small whole-number ratios

5. In chemical reactions, atoms are combined, separated, or rearranged

Dalton is credited as being the Father of the Modern Atomic

Theory

Law of Multiple Proportionsproposed by Dalton

• If 2 or more different compounds are composed of the same two elements, then the ratios of the masses of the 2nd element is always a ratio of small whole numbers– CO (1.0 g C/1.33 g O) – CO2 (1.0 g C/2.66g O)

• 2:1 ratio of O in the compounds– NO (1.0 g N/1.14 g O)– NO2 (1.0 g N/2.28 g O)

• 2:1 ratio of O in the compounds

Benjamin Franklin: 1706-1790American statesman/scientist

Ben’s lightning rod in the Franklin Institute

In 1752 Benjamin Franklin

• Experimented with electricity

• He found that an object can have a positive or a negative charge.

negative and negative: repelnegative and positive: attractpositive and positive: repel

Michael Faraday (1839)English scientist

• Hypothesized that atoms contain electric charge.

• Built 1st electrical motor • Introduced words such as…

– Ion, electrode, anode and cathode• A unit of electricity was named after

him = farad• Static Electricity = electrons move

and then are at rest (grounded)

William Crookes – 1875English scientist

• Cathode Ray Tube: An evacuated glass tube with gas at low pressure

• Electricity is passed through 2 electrodes: cathode (negative) and anode (positive)

• Light is cast from cathode to anode (look at the shadow)

• Magnet deflects light – this proved that particles have charge and mass.

Crookes’ Conclusion

• Light is composed of negatively charged particles – Discovered based upon magnet deflection and

anode shadow

You Tube Demo

Video Clip Crooke’s Tube

Crooke’s Maltese Cross

J.J. Thompson: 1897• English Physicist

who said a cathode ray is made of electrons, they

have mass (9.1 x 10-28g)

and are negatively charged particles. Thus he

is credited with “discovering” electrons.

J.J. Thomson• Used Crookes tube (gas discharge tube)• Applied positive and negative field to a beam

of cathode rays. The deflection was the same for all gases.

• Experimentally proved the existence of the electron (e-)

http://www.aip.org/history/electron/jjappara.htm

Cathode Ray Tube (McGraw Hill)

Experimented with hydrogen gas at low pressure

• 2nd beam of particles was moving towards the cathode, therefore, positive particles

• Deflection of positive ions varied with different gases

• Hydrogen ions had the greatest deflection, therefore, the smallest positive mass

• Hydrogen ion deflection was smaller than that of the electron, therefore more massive than an electron – Hydrogen ion = proton

Thomson

J.J. Thomson• Calculated the charge to mass ratio, (e/m=

-1.76 x 108C/g), using different cathode metals and different gases

• Measured how much they were deflected by a magnetic field and how much energy they carried.

• He found that the charge to mass ratio was over a thousand times higher than that of a hydrogen ion, suggesting either that the particles were very light or very highly charged.

Credit:Science Museum/Science & Society Picture Library

J.J. Thomson• Made a bold conclusion:

– Cathode rays were indeed made of particles which he called “corpuscles," and these corpuscles came from within the atoms of the electrodes themselves, meaning the atoms were, in fact, divisible.

• Won a Nobel Prize in Physics in 1906.

J.J. Thomson: 1897• Thought the atom was made up of these

corpuscles (negative charges) distributed in a sea of positive charge

• Related it to “plum pudding”

Different models of the plum

pudding model

Robert Millikan:1909American scientist

1. Oil drop experiment2. Measured voltage to

determine the charge on one electron -1.60 x 10-19 coulomb/e-

3. Used Thomson’s charge to mass ratio to calculated the mass of an electron

Mass of 1 electron = 9.11 x 10-28g

• An atomizer sprayed a fine mist of oil droplets into the upper chamber. Some of these tiny droplets fell through a hole in the upper floor into the lower chamber of the apparatus.

• Next, Millikan applied a charge to the falling drops by irradiating the bottom chamber with x-rays. This caused the air to become ionized, which means that the air particles lost electrons.

• A part of the oil droplets captured one or more of those extra electrons and became negatively charged

• By attaching a battery to the plates of the lower chamber he created an electric field between the plates that would act on the charged oil drops

• He adjusted the voltage till the electric field force would just balance the force of gravity on a drop, and the drop would hang suspended in mid-air.

• Some drops have captured more electrons than others, so they will require a higher electrical field to stop

• Particles that did not capture any of that extra electrons were not affected by the electrical field and fell to the bottom plate due to gravity.

• When a drop is suspended, its weight  m · g  is exactly equal to the electric force applied, the product of the electric field and the charge q · E.

• The values of E (the applied electric field), m (the mass of a drop which was already calculated by Millikan), and g (the acceleration due to gravity), are all known values. Unknown charge on the drop, q– m · g = q · E

• Millikan repeated the experiment numerous times varying the strength of the x-rays ionizing the air so that differing numbers of electrons would jump onto the oil molecules each time.

• He obtained various values for q. The charge q on a drop was always a multiple of 1.59 x 10-19 Coulombs.

• This is less than 1% lower than the value accepted today: 1.602 x 10-19 C.

Ernest Rutherford: 1903

• Rutherford studies under Thomson.

• He discovered 3 types of natural radiation or radioactive decay.α - Alpha Particlesβ - Beta Particles

γ - Gamma Rays

high energy X-rays

Rutherford’s Gold Foil Experiment 1909

• This experiment showed the atom has a small, central positive nucleus and that most of the atom is empty space.

Rutherford Video Clip

Rutherford’s Gold Foil ExperimentUsed a narrow beam of particles to bombard

targets made of thin sheets of gold. Metal foil was surrounded by a fluorescent screen.Results:• most of the particles passed through the

foil• some were deflected at small angles• few were deflected at large angles

View of the atoms in the Gold Foil Experiment

• Rutherford's Gold Foil Experiment

Conclusions: • atom must contain a very small, dense center of positive

charge • NUCLEUS

• all the positive charge and 99.9% of the mass is in the nucleus• electrons define the space of an atom• electrons move at high speeds around the nucleus• atom does not have uniform density

Rutherford: 1909• After his Gold Foil

Experiment, Rutherford modifies his model of the atom to contain 2 basic regions: a small dense positive nucleus (protons) with electrons outside.

• Proposed a neutral part of the nucleus

Neils Bohr: 1913• Thought the atom was like the solar system

(planetary model). Electrons orbit the nucleus with a fixed energy.

• Energy Levels - analogous to rungs of a ladder• He wins the Nobel Prize for this model in 1922.

It was eventually shown to be inaccurate and too simplistic.

Henry Moseley: 1913• Worked under

Rutherford.• Using CRT’s he

bombarded metals with electrons and observed the emitted X rays by the metals

• Results: each metal produced X rays of unique frequencies or wavelengths (X ray spectral lines)

• Conclusions: He determined that each element has a unique nuclear charge. Hence, a different number of protons (Atomic Number).

• Each atom is electrically neutral and therefore has an equal number of electrons.

• Killed by a sniper in WW in 1915

Moseley cont.

James Chadwick: 1932

• Studied under Rutherford. • 1st isolated a neutron by

bombarding beryllium atoms with alpha particles

• He determined that the atom also contained a neutron which had approximately the same mass as a proton– Mass of proton =

1.673x10-24g– Mass of neutron =

1.675x10-24g• He proposed that the neutron

had a neutral chargeChadwick won the Nobel

Prize for his work in 1935.

Wave (electron cloud) Model:1924 to Present

• Using Quantum Mechanics, the electron can be found in a probability region.

FUN SONGThe atom through the ages…

The Atom Song By Michael Ouffutt

Therefore: • There are 3 subatomic particles: protons,

neutrons and electrons. These are measured in “atomic mass units” (amu) as their mass is so small.

SubatomicParticle Mass (amu) Location Charge

Proton ( p+ )1.673 x 10-27 kg

(1.0073 amu or 1 amu)

In the nucleus +

Neutron ( n0 )1.675 x 10-27 kg

(1.0087 amu or 1 amu)

In the nucleus 0

Electron ( e- )9.1x 10-31 kg

(0.0005 amu or 0 amu)

Outside the nucleus -

Atomic Number and Mass Number

• Atomic Number = the number of protons–Unique to each element– In a neutral atom, the number of

protons equal the number of electrons.

• Mass Number equal to the total number of protons + neutrons in the nucleus of an atom.Ex) carbon-12

IsotopesAtoms that have the same number of protons but a different number of neutrons (mass.)

Isotopic NotationShorthand way of representing an isotope of an

element.

Ex) top number is the mass number (#p + #n)

bottom number is the atomic number (#p)

May also be written: chlorine-37 or Cl-37

The actual average atomic mass for all chlorine isotopes is 35.45 amu

3717 Cl

Isotopes of Hydrogena. hydrogen (hydrogen – 1) 1p+ 0n0

b. deuterium (hydrogen – 2) 1p+ 1n0

c. tritium (hydrogen – 3) 1p+ 2n0

11H21H31H

Isotope ProtonsNeutro

ns

Mass Numbe

r

Electrons

Isotopic

Notation

Carbon-12 6 6 12 6

Carbon-13 6 7 13 6

Carbon-14 6 8 14 6

126C

146C

136C

Ions• Formed when an atom gains or loses an

electrona. Charge = # of protons - # of electrons

Ex) Mg +2 = lost 2 electrons # of protons: 12 # of electrons:

10 Charge: +2Positively Charged ion - CATION

Ex) N-3 = gained 3 electrons # of protons: 7 # of electrons: 10

Charge: -3Negatively Charged ion - ANION

Isotope Protons Neutrons

Mass Number

Electrons

Isotopic Notatio

nCharge

Mg-25 12 13 25 10 +2

N-14 7 7 14 10 -3

Br-79 35 44 79 36 -1

79 135 Br

14 37 N

25 212 Mg

Atomic Mass:• The mass of an atom expressed in amu (atomic

mass units.)

• One amu is equal to 1/12 the mass of a carbon-12 atom.Average Atomic Mass:

• The weighted average of all an element’s isotopes.

• Mass Spectrometers are instruments used to measure masses of isotopes as well as their isotopic abundance.

• This is the number shown in the box on the Periodic Table.

• It is calculated by: (mass1 x %1) + (mass2 x %2) + …

Weighted Average Grade Example:

Straight Class

93% Tests90% HW70%

Participation

84.3% Average

Weighted Class

x 70% = x 20% =x 10% =

Weighted Average:

90.1%

Ex) carbon

C-12C-13C-14 ? Straight

Average 13???Actual

AverageAtomic Mass

= 12.011 amu

Ex) hydrogen

H-1H-2H-3 ? Straight Average 2???Actual

AverageAtomic Mass

= 1.0079 amu

Calculation of atomic mass

Magnesium has 3 naturally occurring isotopes:78.99% Mg-24, 10.00% Mg-25, and

11.01% Mg-26

Calculate the atomic mass of magnesium. (24 x 0.7899) = 18.9576 = 18.96+ (25 x 0.1000) = 2.500 =

2.500+ (26 x 0.1101) = 2.8626 = 2.863

24.323 24.32 amu

Calculation of atomic mass

Magnesium has 3 naturally occurring isotopes:

78.99% is 23.98504 amu10.00% is 24.98584 amu11.01% is 25.98259 amu

Calculate the atomic mass of magnesium. (23.98504 amu x 0.7899) + (24.98584 amu x 0.1000) + (25.98259 amu x 0.1101)

24.31 amu

Question: Can we count atoms?

Atoms are too small to count or mass individually. It is easier to count many or mass many.

amu gram (atomic scale) (macroscopic scale)

mole

Getting to know the terms…

MICROSCOPIC

Mass MACROSCOPIC Molar Mass

Atom Atomic mass

amu Element g/mol

Molecule Molecular mass

amu Molecular

Compound g/mol

Formula UnitFormula mass

amu Ionic

Compound g/mol

Diatomic Molecules H2 O2 F2 Br2 I2 N2 Cl2

• 1) The mole is defined as the number of atoms in exactly 12 grams of carbon-12.

• 2) The number of particles in a mole is called Avogadro’s number. (6.02 x 1023)

Avogadro’s Number and the Mole

MOLE RELATIONSHIPS

1 Mole = 6.02x1023 particles of substance

(atoms, formula units, molecules)

1 Mole = mass (g) of substance from PT

• An Avogadro's number of standard soft drink cans would cover the surface of the earth to a depth of over 200 miles.

• If you had Avogadro's number of unpopped popcorn kernels, and spread them across the United States of America, the country would be covered in popcorn to a depth of over 9 miles.

• If we were able to count atoms at the rate of 10 million per second, it would take about 2 billion years

• 6.02 X 1023 Watermelon Seeds: Would be found inside a melon slightly larger than the moon.

Mole Analogies

• 6.02 X 1023 Donut Holes: Would cover the earth and be 5 miles (8 km) deep.

• 6.02 X 1023Pennies: Would make at least 7 stacks that would reach the moon.

• 6.02 X 1023 Grains of Sand: Would be more than all of the sand on Miami Beach.

• 6.02 X 1023 Blood Cells: Would be more than the total number of blood cells found in every human on earth.

Mole Analogies

• Mass of an atom

• Carbon– 12.0 amu

• Oxygen– 16.0 amu

What is atomic mass?

• Mass in grams of one mole of an element or compound, is numerically equivalent to the atomic mass of monatomic elements and the formula mass of compounds and diatomic elements. (Unit = g/mol)

• Carbon– Atomic mass = 12.0 amu– Molar Mass = 12.0 g/mol

• Magnesium– Atomic mass = 24.3 amu– Molar Mass = 12.0 g/mol

What is molar mass?

Nuclear Energy

1. Nuclear Reactions: Change the composition of an atom’s nucleus.

2. The strong nuclear force holds the nucleus together.

3. Most atoms are stable (equal number of p & n). These are the smaller

atoms which are NOT

radioactive.

4. Unstable nuclei have more neutrons than

protons. These isotopes are radioactive.

5. As the elements become larger they become

more unstable.6. All elements have at least 1

radioactive isotope. All the isotopes of those elements with atomic numbers greater than 83 are radioactive.

7. The larger nuclei are radioactive because

they have more neutrons than protons.

There are 265 stable nuclei• 159 have even # of p+ & even # of n0 • 52 have even # of p+ and odd # of n0

• 50 have odd # of p+ and even # of n0

• 4 have odd #’s of both p+ and n0

Special stability if # of p+ or # of n0 or their sum = 2, 8, 20, 28, 50, 82, or 126 (MAGIC #’s)

• Indicates stability of nucleus is greatest when nucleons are paired and exist in different energy levels (shells) in the nucleus

• Suggests an architecture within the nucleus…Nuclear Shell Model

# of protons

# of

neutrons

20

20 40

40

60

60 80

80

Composition of Stable Nuclei

Unstable Nucleus

Characteristics of Subatomic Particles and

Rays:Particle Mass

(amu) ChargeSymbol

Stopped by

Proton1.00727647

Neutron1.00866490

Beta Particle

(electron)

0.00054858

Alpha Particle

(He nucleus)

4.00150617

Gamma Ray

0

+1

0

+2

0Several

centimeters of lead

paper

Heavy clothing/Al

foil

Few centimeters of

lead

paper

-1

p+ or

n0 or

11H

10 n

0 01 -1e or β

4 42 2He or α

00 γ or E

Nuclear Radiation Penetrating Power

Nuclear Radiation Penetrating Power

Spontaneous Emission of Radiation:

A. Unstable nuclei will spontaneously emit 3 types of natural radiation, this is also called radioactive decay.

B. When an atom emits 1 kind of radiation the original nucleus decomposes or decays to form a new nucleus and releases radiation. This is written in a nuclear equation.

Alpha & Beta Decay

3 Types of Spontaneous Radiation:

A. Alpha Decay – spontaneous emission of alpha particle from the nucleus.

B. Beta Decay – spontaneous emission of beta particle from the nucleus

C. Gamma Decay – spontaneous emission of gamma ray from the nucleus

18177Ir226 222 4

88 86 2Ra Rn α 185 479 2Au _________ α

14 06 1C ________ β

238 092 0U ________ γ

147 N

23892U

131 13153 54I Xe + _____

01β

Uranium Radioactive Decay Series

How Radon Gas Enters your House

Ways to Remove Radon Gas from Your Home

• External view of a Radon mitigation system from a home basement.

• Below is a view of the fan inside which runs 24 hours a day pulling air from under the basement floor.

Testing Methods for Radon

U.S. Radon Zones

Nuclear Bombardment Reactions:

A. Process in which a new element is formed by bombarding a nucleus with small energetic particles.

B. The energetic particle hits the nucleus and forms an unstable compound nucleus, which is short-lived.

C. This nucleus can emit another particle to stabilize itself.

D. This is the process used in particle accelerators where artificial isotopes and transuranium elements have been produced.

E. Sometimes referred to as “capture” in an equation.

Particle Accelerator in Switzerland with a 16.7 mile

circumference

Nuclear Bombardment Reaction

14 4 18 17 17 2 9 8 1[ ]N He F O H

target nucleus

projectile new isotope (element)

ejected particle

Nuclear Fission

A. Process by which a heavy nucleus splits into two smaller nuclei.

B. Most fission reactions are induced.C. The energy yield for fission reactions are

very high.D. Fission reactions are the source of energy

used to generate electricity in nuclear power plants.

E. U-235 & Pu-239 are the radioisotopes used in reactors.

Nuclear Fission Reaction

235 1 236 93 140 192 0 92 36 56 0[ ] 3U n U Kr Ba n

Nuclear fuel

projectile – particle that starts the chain reaction

temporary unstable nuclei that immediately splits

into 2 approximately equal mass product nuclei

3 neutrons are produced which start additional fission reactions

F. In fission reactions, the product nuclei have far too

many neutrons, and are intensely radioactive. This

is considered radioactive waste.

G. The released neutrons can cause another reaction as

long as sufficient U-235 remains.

H. This is called a chain reaction.

I. The smallest amount (minimum volume) of fissionable material needed to sustain a

chain reaction is called the critical mass.

Nuclear Chain Reaction

Fuel: U-235 or Pu-239

Critical mass for U is 110 lbs

Nuclear Fusion:A. This is a thermonuclear reaction - requires high

temperatures.B. Occurs when two small nuclei fuse, or join, to form

larger, more stable nuclei.C. Releases a large amount of energy.D. Process that occurs on the sun and in a hydrogen bomb.E. If fusion reactions are going to be practical, they need to produce more energy than they require to get started. F. In a fusion reaction, the starting materials are in a form of plasma. G. The biggest problem is obtaining the high temperatures necessary for a fusion reaction to occur.

H. A “magnetic bottle” is used to hold plasma at high temperatures.

3 2 4 1 121 1 2 0H H He n 1.7x10 J/mol

neutron

U-235 Energy

Krypton-92

3 neutrons

Barium-141

21H

21H

11H

11H

11H

11H

42 He

Energy

Fission

Fusion

Nuclear Power Plants/A-bomb

The Sun/

H-bomb

A wooden house built 1km away from the test site…

The first Atomic Bomb is detonated at Trinity Site near Alamogordo, New Mexico on July 16, 1945.

A Monument stands at the test site today.

shows the result of the blast.

“Little Boy” Uranium fission bomb dropped on Hiroshima,

Japan by the “Enola Gay” flown by

Colonel Paul Tibbets

Hiroshima - August 6, 1945Distance fromGround Zero (km)

Killed Injured Population

 0 -1.0 86% 10%   31,020

1.0 - 2.5 27% 37% 144,800

2.5 - 5.0 2% 25%   80,300

Total 27% 30% 256,300

Hiroshima 1945 & Today

Nagasaki - August 9, 1945Distance fromGround Zero (km)

Killed Injured Population

 0 -1.0 88%  6%   30,900

1.0 - 2.5 34% 29% 144,800

2.5 - 5.0 11% 10%   15,200

Total 22% 12% 173,800

“Fat Man” – Plutonium Fuel

U.S. Nuclear Testing• Large craters pockmark Frenchman Flats,

Nevada, a former test site for U.S. nuclear weapons. The US conducted more than 1050 tests here and in Alaska, Colorado, Mississippi, New Mexico between 1945 and 1992.

• The Soviet Union, UK, France, China, India and Pakistan had a similar total number of tests over the same time period.

Fusion Bombs• The first thermonuclear weapon

(hydrogen bomb), code-named Mike, was detonated at Enewetak atoll in the Marshall Islands, Nov. 1, 1952. The photograph was taken at an altitude of 12,000 feet over 50 miles from the detonation site.

• Only 6 countries have detonated a hydrogen bomb – US, UK, Soviet Union, France, China and India.

• To obtain temperatures in the millions of degrees Celsius a fission reaction is set off first to start the fusion reaction.

Nuclear ReactorsA. There are currently 111 commercial nuclear

power plants in the U.S. They provide 20% of our country’s electricity, but 80% of the

electricity used in southeastern PA.

B. There are 530 nuclear reactors in 30 nations around the world that provide 1/6 of the

world’s electricity. To produce electricity you need to turn a turbine. This can be accomplished by wind or water, must most commonly by steam. The only difference between a nuclear power plant and a conventional fossil fuel plant is the method used to produce boiling water.

14. Parts of a Nuclear Reactor

A.Fuel Rods: Composed of 97% U-238 and 3% U-235 (the fissionable isotope). Chalk- sized

pellets are arranged in long steel cylinders in the reactor core. When the fuel has given up most of its energy it is called spent. It will be reloaded every 1 to 3 years. There can be 10,000,000 pellets in 1 plant.

B. Control Rods control the rate of a nuclear reaction. Without them the reaction would occur too fast for it to be effective.

C. Moderator is usually heavy water (D2O). Without sufficient cooling of the core a meltdown could occur. This water also shields workers.

View of fuelrods andcontrol rodsimmersed in“heavy water.”

D. Generator produces electricity by turning a steam turbine from the boiling water.

E. Cooling System: Water from outside is used to cool the steam (it does not come into contact with the cooling water in the core). Excess steam rises up in the cooling tower, condenses and falls back.

Parts of a Nuclear Reactor con’t.

Cooling Towers

Limerick, PA

Nuclear Power Plant Diagram

Radioactive Waste:

A. Spent fuel rods have been accumulating for about 40 years. Spent fuel rods are highly radioactive,

with some isotopes remaining active for thousands of years. By federal law reactor waste must be

stored on site. The U.S. Government has not yet opened any permanent storage sites, but one called

Yucca Mountain in Nevada is currently being

negotiated. On-site storage is only a temporary measure, as tanks require too much maintenance

to be safe for long term storage.

Radioactive Waste• Radioactive

waste is stored under water until it decays to lower levels.

Radioactive Warning Symbol

• Waste is transferred to storage casks and stored on-site at each power plant.

Temporary Radioactive Waste Storage

Nuclear Accidents• Three Mile

Island March 28, 1979 on the Susquehanna River near Harrisburg, PA. The worst nuclear accident in U.S. history was caused by technical failures and human error. About 2 million people were exposed to 1mrem of radiation which led to no deaths or injuries.

• Chernobyl April 26, 1986 in the northern Ukraine. The core melt meltdown caused radioactive materials to spread over a wide area of Europe. Officials at a Sweden Nuclear Power Plant 1st noticed that radioactive particles were on their clothes and thought their own plant was malfunctioning. The worst nuclear accident in the world was caused by a flawed reactor design and inadequately trained operators.

Nuclear Accidents

• 57 immediate deaths with 4000 additional cancer deaths long term. Over 360,000 people were evacuated permanently from the area which remains closed. The initial cover-up of the incident made clean up worse.

• Japan 2011An earthquake and resulting tsunami caused the reactors at the Fukushima plant in Japan to lose power. Without power and functioning back-up generators, the core in three reactors overheated and melted. Multiple explosions, fires, and gas releases complicated the problem. Also, contaminated water was released into the environment. People were forced to evacuate, and clean-up is still underway.

Nuclear Accidents

Uses for Nuclear Chemistry:

A. Half life 1. The time required for ½ of the

atoms of a radioactive isotope to decay.

2. Using radioactive isotopes to determine the age of an object is called radio carbon dating.

Ex. If I have 1.00 mg of , which has a ½ life of 8.04 days, how much will be left after 1 half-life? After 2? After 3?

13153 I

B. Radioactive Isotopes and Dating

1. All animals and plants contain carbon-14.

2. Even though carbon-14 undergoes radioactive decay, it is constantly replenished during a lifespan.

3. The half-life of carbon-14 is 5730 years.

4. The ratio of C-12 to C-14 is compared to

another object of a similar age.5. Cannot use carbon-14 dating with

objects that never lived.

6. After 4 half lives, the amount of carbon-14 remaining is too small to give reliable data.

7. Carbon-14 is not useful for specimens over 25,000 years old, so Potassium-40

is used instead. It has a half-life of 1.28 billion years.

Radioactive Decay of Strontium-90

What is the ½ Life of Strontium-90??? 28 years

How long until no more Strontium-90 remains?

What is the ½ Life of this Radioactive Sample?

2 days

Smoke Detectors: 1. Smoke detectors emit a small amount of

alpha particles.2. When smoke particles mix with the gas,

they slow the current flow setting off the alarm.

Medical Uses

1. CAT SCAN – the body is analyzed using X-rays.

2. MRI and NMR – detects body’s absorption of radio waves.

3. PET – Measures gamma rays from certain part of the brain.

4. Radioisotopes prepared in a nuclear reactor can be used to both treat and detect various medical conditions. Tracers can be used to follow a particular isotope through its normal path in the body to show any abnormalities.

Ex) Upper and Lower GI uses

radioactive Barium to detect stomach and intestinal problems. An IVP measures the bodies absorption of radioactive iodine to detect kidney stones.

5. Irradiation can be used as an energy source to treat cancer. The diseased area is exposed to ionizing radiation to kill cancerous cells.

Ex) Ingest large amounts of I-131 kills thyroid cancer, External beam of Co-60 can be directed at a cancerous spot. Irradiation can also be used to sterilize medical instruments and preserve food.

Food Irradiation Symbol

Exposure to Radioactivity:

A. Continued exposure to radiation is dangerous; therefore, people working in these conditions must monitor their exposure to radiation.

B. People working with radiation wear film badges to monitor their exposure.

C. A dosimeter measures radiation in people, a

Geiger Counter measures radiation of objects.

D. Radiation is usually measured in units of mrems. Higher doses for a longer period of time over a large area cause the most damage, especially for rapidly dividing cells like sex cells and blood cells.

Sources of Our Radiation Exposure