Nuclear Chemistry M. Jones Pisgah High School Last revision: 100211.

Nuclear Chemistry M. Jones Pisgah High School Last revision:

Nuclear chemistry studies
Atomic theory Radioactivity Isotopes Half-life Decay equations Energy, fission and fusion

Atomic Theory

Atomic Theory Atoms are the smallest particles of elements.
Atoms were first proposed by Democritus over 2000 years ago. The idea of atoms was reintroduced in 1803 by John Dalton.

Dalton’s Atomic Theory
Atoms are tiny, discrete particles Atoms are indestructible Atoms of the same element have the same mass and properties Atoms combine in simple whole-number ratios Atoms in different ratios produce different compounds.

Atoms are tiny, discrete particles Atoms are indestructible Atoms of the same element have the same mass and properties Atoms combine in simple whole-number ratios Atoms in different ratios produce different compounds. We know that parts of Dalton’s atomic theory are no longer valid in today’s modern Quantum Mechanical model of the atom.

Atoms are tiny, discrete particles Atoms are indestructible Atoms of the same element have the same mass and properties We know that atoms are made up of smaller particles, and that there are slight differences between atoms of the same element - isotopes.

William Crookes Used spectroscopy to discover thallium and used vacuums to measure its mass. Invented the radiometer. Improved vacuum systems. Used by Edison to make light bulbs.

William Crookes What we now call the cathode ray tube.
The Crookes’ Tube

William Crookes Used the cathode ray tube to to study electric fields in a vacuum and discovered rays, … which were called “cathode rays” by Goldstein, since they came from the cathode, or negative electrode.

William Crookes The shadow of the Maltese cross indicates that cathode rays travel in straight lines and can be stopped by a solid object.

William Crookes He found that the cathode rays could be deflected by a magnet. This suggested that the cathode rays might be a stream of electrically charged particles.

Cathode Ray Tube + Cathode Anode Direction of cathode rays
High voltage

Cathode Ray Tube + Cathode Anode Direction of cathode rays Magnet
High voltage

to discover the electron.
Cathode Ray Tube Used by J. J. Thomson … to discover the electron. Cathode Anode + High voltage

J.J. Thomson and Cathode Rays
Attracted to positive electrode Thought might be atoms Had same charge to mass ratio regardless of metal in the cathode The particle was much less massive than the lightest element – H Particle must be common to all matter, a subatomic particle

In 1897 J. J. Thomson found that cathode rays are a basic building block of matter. He had discovered the electron.

The term “electron” comes from George Stoney’s term for the “minimum electrical charge”. Thomson concluded that this particle was the carrier of the minimum electrical charge and so the particle was later called an “electron”.

Even though Crookes and others observed cathode rays, Thomson is credited with the discovery of the electron because he recognized that it was a fundamental particle of nature as well as a sub-atomic particle.

Measured the charge to mass ratio, and found … … that if this “minimum charge” was equal to the charge on a hydrogen ion, then the mass of the electron would be 1/1837th the mass of a hydrogen atom.

If that were the case, then the electron would be much smaller than the smallest atom ..… showing for the first time that matter is made up of particles smaller than atoms. Thomson tried to measure the fundamental charge on the electron.

Robert A. Millikan Robert A. Millikan, an American physicist, set out to determine the charge on an electron. From 1909 through 1910, he performed what is now called the “Oil Drop Experiment”.

Robert A. Millikan Atomizer High Voltage Telescope Cast iron pot

Robert A. Millikan Atomizer Parallel charged plates High Oil Drop
Voltage Oil Drop Telescope Cast iron pot

Robert A. Millikan Radiation stripped electrons from the oil droplets. The charged droplets fell between two electrically charged plates. By adjusting the voltage, he could change the rate of fall or rise of a single oil drop. After observing hundreds of drops, he calculated the charge on a single electron.

Charges on drops are multiples of
Robert A. Millikan Charges on drops are multiples of 1.602 x coulombs.

Robert A. Millikan 9.109 x 10-28 gram
The fundamental charge on an electron is x coulombs. With J. J. Thomson’s charge to mass ratio, and Millikan’s charge on the electron, we are able to compute the mass of an electron: 9.109 x gram

Ernest Rutherford He is to the atom what Darwin is to evolution, Newton to mechanics, Faraday to electricity and Einstein to relativity. John Campbell

Ernest Rutherford He moved from New Zealand to Cambridge University in England (1895) where he pioneered the detection of electromagnetic waves, but was lured away by J.J. Thomson on work that would lead to the discovery of the electron. The invention of radio communications went to Marconi, instead. He later switched to working with radioactivity (1896) and discovered alpha and beta rays. He went to Montreal to teach at McGill University (1898) where he continued his work on radioactivity with Frederick Soddy, and others ( ). He moved back to back to England to teach at Manchester (1907). He received the Nobel prize in chemistry in 1908 for his work on radioactivity in Canada.

Ernest Rutherford In 1907, he and a student, Hans Geiger, developed what would later become the “Geiger counter”. While at McGill, Rutherford discovered that after alpha rays passed through a thin film of mica, the image formed on a photographic plate was “fuzzy”. He and Geiger began a project to investigate the scattering of alpha particles by thin films. Rutherford later gave Ernest Marsden, an undergraduate, his own research project which was to look for evidence of the backscatter of alphas (1909). To their surprise, Marsden found that some alpha particles were scattered backwards from thin films of lead, platinum, tin, silver, copper, iron, aluminum, and gold.

Ernest Rutherford Rutherford remarked that it was like firing a navel gun at a piece of tissue paper and the shell bouncing back and hitting you. By 1910, Hans Geiger had finished his research on the forward scattering of alpha particles but he could not reconcile it with Marsden’s observations of the backscatter of alphas. The problem was passed on to Rutherford, who came up with the answer, and the astounding results were published in 1911.

Ernest Rutherford Rutherford had discovered a new piece to the atomic puzzle, the nucleus. According to Rutherford, the positively charged alpha particles were encountering a tiny, positively charged particle within the atoms of the metal and were being repelled. The atoms themselves appeared to mostly empty space. It was the repulsion of two positively charged particles which caused the scattering observed by Geiger and Marsden. Rutherford had found that atoms are mostly empty space with a small, dense, positively charged nucleus.

Alpha scattering Apparatus for investigating alpha scattering.
What some textbook authors call the “gold foil experiment.”

+ Alpha scattering a source
Most of the alpha particles pass through undeflected.

+ Alpha scattering a source
Some positive alpha particles are repelled by the small, dense, positively charged nucleus. +

Alpha scattering Alpha particles are repelled by a small, dense, positively charged nucleus. Almost all the mass of an atom is in the nucleus. Atoms are mostly empty space. Electrons are located outside the nucleus. Published results in 1911.

Ernest Rutherford N + a  O + H
Rutherford, during the First World War, worked on developing SONAR and submarine detection, but still found time to tinker with alpha radiation. In 1917 he bombarded nitrogen gas with alpha particles and discovered that oxygen and hydrogen were produced. Rutherford had resorted to alchemy and accomplished the first transmutation of one element into another. He had also indirectly discovered the proton. N + a  O + H

Ernest Rutherford N + a  O + H We now know… 7 protons 1 proton

Ernest Rutherford Rutherford concluded that the nucleus must contain the positively charged protons in a number equal to the negative charge from the electrons, but this did not account for all of the mass of the atom. He, along with James Chadwick, rejected the idea that there must be additional protons and electrons in the nucleus, and concluded that there must be a neutral particle in the nucleus that accounted for the additional mass. In 1932, Chadwick confirmed the existence of the neutron.

Radioactivity

Demonstrations with radioactivity
Investigate the properties of Alpha, Beta and Gamma Radiation

Geiger-Mueller Tube Counter Wire (+ side of circuit)
2435 Wire (+ side of circuit) Metal shield (- side) Low pressure Ar gas Mica window (fragile)

Geiger-Mueller Tube Rays leave the source Some hit the GM tube
Most do nothing One ray may cause a discharge… Source and the detector clicks

Geiger-Mueller Tube Filled with low pressure argon gas
About 1% efficiency About 1 in 100 rays causes an electric spark between the case and the wire Each spark registers as a count or click on the counter

Radioactivity a helium nuclei b electrons g
Alpha particles Beta particles Gamma rays a b g helium nuclei electrons high energy electromagnetic energy - similar to light, but higher in energy.

Radioactivity Alpha particles
An unstable nucleus splits to form a more stable nucleus an an alpha particle. An alpha particle is the nucleus of a helium atom. Two protons and two neutrons. Has a +2 charge.

Radioactivity Beta particles
Ejected from the nucleus when a neutron decays. A beta particle is identical to an electron Has a -1 charge.

Radioactivity Gamma rays
Emitted by an unstable nucleus as it becomes more stable Electromagnetic energy with short wavelengths and high energy. Has no charge.

Radioactivity - comes from the natural decay of unstable atoms.
- can be detected by photographic film, scintillation detector or a Geiger counter. - is “ionizing radiation”. Causes cell damage and mutations – cancer. - is protected against by shielding and distance.

E Mass number /Atomic number A Z Mass number protons
+ neutrons Protons in nucleus E A Mass number Z Symbol of Element Atomic number

U Mass number /Atomic number 235 92 Mass number protons
+ neutrons Protons in nucleus U 235 Mass number 92 Symbol of Element Atomic number

Radioactivity Alpha (a) particles are the nuclei of helium atoms and have the symbol 2He4. What is the atomic number of an a particle? 2 He4

Radioactivity Alpha (a) particles are the nuclei of helium atoms and have the symbol 2He4. What is the mass number of an a particle? 2 He4

Radioactivity Alpha (a) particles are the nuclei of helium atoms and have the symbol 2He4. 4 How many times heavier is an alpha particle than a hydrogen atom?

Radioactivity Beta (b) particles are high speed electrons ejected from the nuclei of atoms and have the symbol -1e0. What is the mass number of a b particle? -1e0

Radioactivity Beta (b) particles are high speed electrons ejected from the nuclei of atoms and have the symbol -1e0. No protons or neutrons in an electron. -1e0

Radioactivity Beta (b) particles are high speed electrons ejected from the nuclei of atoms and have the symbol -1e0. What is the difference between a b particle and a “regular” electron? None

Radioactivity Location
Beta (b) particles are high speed electrons ejected from the nuclei of atoms and have the symbol -1e0. What is the difference between a b particle and a “regular” electron? Location

Radioactivity Gamma (g) rays are high energy electromagnetic waves, not particles. No protons, neutrons or electrons. Gamma rays have short wavelengths, high energies and travel at the speed of light.

Gamma rays have short wavelengths
Increasing energy … and high energies.

What is the effect of an electric field on a, b, g ?
Alpha, Beta, Gamma Electric field from electrically charged plates What is the effect of an electric field on a, b, g ? Radioactive Source

Alpha, Beta, Gamma b g a - - - - - - - - - Radioactive Source
Electric field from electrically charged plates b g a Radioactive Source

Alpha, Beta, Gamma b Are a, b and g rays deflected by magnetic fields?
Electric field from electrically charged plates b Are a, b and g rays deflected by magnetic fields? g a Radioactive Source

Alpha, Beta, Gamma Paper Lead a Aluminum foil Radioactive Source

Alpha, Beta, Gamma Paper Lead b a Aluminum foil Radioactive Source

Alpha, Beta, Gamma Paper Lead b g a Aluminum foil Radioactive Source

Radiation Project Create a table listing information for each of the three kinds of radiation: Alpha, beta and gamma

Properties to include in your table:
Greek letter symbol actually is atomic number mass number relative mass relative. charge penetrating ability shielding

Stop! Complete the chart on notebook paper, then continue.
Nuclear Properties Table Property Alpha Beta Gamma Greek Letter Symbol Actually is… Atomic number Mass number Relative mass Relative charge Penetrating Shielding Stop! Complete the chart on notebook paper, then continue.

Nuclear Properties Table
Property Alpha Beta Gamma Greek Letter Symbol Actually is… Atomic number Mass number Relative mass Relative charge Penetrating Shielding

Property Alpha Beta Gamma Greek Letter a b g Symbol Actually is… Atomic number Mass number Relative mass Relative charge Penetrating Shielding

Property Alpha Beta Gamma Greek Letter a b g Symbol 2He4 -1e0 NA Actually is… Atomic number Mass number Relative mass Relative charge Penetrating Shielding

Property Alpha Beta Gamma Greek Letter a b g Symbol 2He4 -1e0 NA Actually is… He nucleus electron EM energy Atomic number Mass number Relative mass Relative charge Penetrating Shielding

Property Alpha Beta Gamma Greek Letter a b g Symbol 2He4 -1e0 NA Actually is… He nucleus electron EM energy Atomic number 2 -1 Mass number Relative mass Relative charge Penetrating Shielding

Property Alpha Beta Gamma Greek Letter a b g Symbol 2He4 -1e0 NA Actually is… He nucleus electron EM energy Atomic number 2 -1 Mass number 4 Relative mass Relative charge Penetrating Shielding

Property Alpha Beta Gamma Greek Letter a b g Symbol 2He4 -1e0 NA Actually is… He nucleus electron EM energy Atomic number 2 -1 Mass number 4 Relative mass 1/1837 Relative charge Penetrating Shielding

Property Alpha Beta Gamma Greek Letter a b g Symbol 2He4 -1e0 NA Actually is… He nucleus electron EM energy Atomic number 2 -1 Mass number 4 Relative mass 1/1837 Relative charge +2 Penetrating Shielding

Property Alpha Beta Gamma Greek Letter a b g Symbol 2He4 -1e0 NA Actually is… He nucleus electron EM energy Atomic number 2 -1 Mass number 4 Relative mass 1/1837 Relative charge +2 Penetrating Low Medium High Shielding

Property Alpha Beta Gamma Greek Letter a b g Symbol 2He4 -1e0 NA Actually is… He nucleus electron EM energy Atomic number 2 -1 Mass number 4 Relative mass 1/1837 Relative charge +2 Penetrating Low Medium High Shielding 2.5 cm of air; anything else Metal, plastic or wood Lead or concrete

Protection from radiation
Shielding 2. Distance How do you protect yourself from … Alpha Beta Gamma 2.5 cm of air, paper, skin aluminum, lead, other metals, wood, plastic, etc. up to a foot or two of lead, many feet of concrete

There are some kinds of radiation you can not protect your self from.

Radiation Gamma rays and high energy cosmic particles from space.
But there is one kind of radiation hazard that you can protect against.

That hazard comes from the uranium beneath your feet.
Uranium in the ground decays according to …

The uranium decay series
Uranium-238 decays through many steps to make stable lead-206

The uranium decay series
Radon is the only gas in the series.

Hazards from radon Since radon is the only gas in the decay series of uranium … …it can work its way up through the ground and into your basements and crawl spaces. You breathe radon into your lungs.

Hazards from radon And when radon is in your lungs…
…it can decay and release an alpha particle … …which travels only a short distance before it is absorbed by your lungs, and transfers its energy.

Hazards from radon This ionizing radiation in your lungs can cause lung cancer. Smoking cigarettes and breathing radon really increases your chances of getting lung cancer.

Protecting against radon
Get a test kit to see if there is a problem. Charcoal canisters, which are sent off for analysis. Abatement: Seal places where gas gets in. Ventilation – bring in fresh air.

Atomic Theory We know that atoms are mostly empty space.
We know that atoms are made up of protons, neutrons and electrons. Protons and neutrons are located in a small, dense, positively charged nucleus.

Atomic Theory We know atoms are mostly empty space and that protons and neutrons are located in a small, dense, positively charged nucleus because of Rutherford’s explanation of Geiger and Marsden’s work in alpha scattering (gold foil experiment ).

Atomic Theory We know that electrons are outside the nucleus in an “electron cloud”. Electrons exist in specific energy levels, which explains the line spectra of the elements. Started with the Bohr model.

Atomic Theory We now use the Quantum Mechanical Model of the atom.
Quantum Theory describes the nature of electrons and their interactions with the electrons of other atoms in chemical reactions.

Atomic Theory The subatomic particles that make up atoms have known properties like mass and electrical charge. Our understanding came through the efforts of a number of scientists like Thomson, Millikan, Rutherford, and Chadwick.

U Mass number /Atomic number 235 92 Mass number protons
+ neutrons Protons in nucleus U 235 Mass number 92 Symbol of Element Atomic number

n H e Subatomic particles What do the numbers represent? proton
1 proton electron H 1 neutron e -1 What do the numbers represent?

Fill in the chart with the correct information.
Property Proton Neutron Electron Symbols Location Rel. mass Mass (amu) Mass (g) Rel. charge Charge (C) Fill in the chart with the correct information.

Proton Neutron Electron
Property Proton Neutron Electron Symbols p+ and 1H1 n0 and 0n1 e- and -1e0 Location Rel. mass Mass (amu) Mass (g) Rel. charge Charge (C)

Property Proton Neutron Electron Symbols p+ and 1H1 n0 and 0n1 e- and -1e0 Location nucleus cloud outside nucleus Rel. mass Mass (amu) Mass (g) Rel. charge Charge (C)

Property Proton Neutron Electron Symbols p+ and 1H1 n0 and 0n1 e- and -1e0 Location nucleus cloud outside nucleus Rel. mass 1 1/1837 Mass (amu) Mass (g) Rel. charge Charge (C)

Property Proton Neutron Electron Symbols p+ and 1H1 n0 and 0n1 e- and -1e0 Location nucleus cloud outside nucleus Rel. mass 1 1/1837 Mass (amu) amu amu amu Mass (g) Rel. charge Charge (C)

Property Proton Neutron Electron Symbols p+ and 1H1 n0 and 0n1 e- and -1e0 Location nucleus cloud outside nucleus Rel. mass 1 1/1837 Mass (amu) amu amu amu Mass (g) 1.673x10-24 1.675x10-24 9.11x10-29 Rel. charge Charge (C)

Property Proton Neutron Electron Symbols p+ and 1H1 n0 and 0n1 e- and -1e0 Location nucleus cloud outside nucleus Rel. mass 1 1/1837 Mass (amu) amu amu amu Mass (g) 1.673x10-24 1.675x10-24 9.11x10-29 Rel. charge +1 -1 Charge (C)

Property Proton Neutron Electron Symbols p+ and 1H1 n0 and 0n1 e- and -1e0 Location nucleus cloud outside nucleus Rel. mass 1 1/1837 Mass (amu) amu amu amu Mass (g) 1.673x10-24 1.675x10-24 9.11x10-29 Rel. charge +1 -1 Charge (C) +1.6x10-19 C -1.6x10-19 C

Subatomic particles Protons and neutrons are located in the nucleus.
Protons and neutrons have almost the same mass. Neutrons heavier. Electrons are outside the nucleus and much lighter than proton or neutron. Protons and electrons have the same charge but opposite polarity. Neutrons have no charge.

Subatomic particles Protons and neutrons are each made of smaller particles called quarks. Quarks are elementary particles just like electrons. They are not composed of smaller particles. There are six kinds of quarks: “up”, “down”, “top”, “bottom”, “charm” and “strange”.

Subatomic particles Protons are composed of two “up quarks” and one “down quark”. Neutrons are composed of two “down quarks” and one “up quark”. Quarks are held together to make protons and neutrons by the strong force, the strongest of the four fundamental forces in nature. Gravity, electromagnetism, weak and strong.

Isotopes

Isotopes … …of the same element have the same number of protons and electrons but different numbers of neutrons. Therefore, isotopes of the same element have different masses.

Isotopes … …don’t have to be radioactive.
Some isotopes are unstable and decay, releasing alpha or beta particles, or gamma rays. But, there are many stable isotopes that don’t decay.

Isotopes … …have different mass numbers but the same atomic number.
Atomic number - the number of protons in the nucleus of an atom. Mass number - the sum of the protons and neutrons in the nucleus.

E Symbols for Isotopes A is the symbol for mass number A Z
Symbol of Element E Z Atomic number Z is the symbol for atomic number

U Symbols for Isotopes 235 92 An isotope of uranium Mass number
Symbol of Element U 92 Atomic number An isotope of uranium

U Symbols for Isotopes An isotope of uranium Mass number 235 92
This form solves the word processor dilemma. U 235 92 Symbol of Element Atomic number An isotope of uranium

U-235 Symbols for Isotopes Z = 92 How do you know the atomic number?
Symbol of Element Find U in the periodic table. Z = 92 U-235 Mass number How do you know the atomic number?

Some elements have several Isotopes
Lead has four naturally occurring isotopes, Pb-204, Pb-206, Pb-207, and Pb-208; but there are 23 man-made isotopes of lead.

Some elements have several Isotopes
Bismuth has only one naturally occurring isotope, Bi-209, but there are 22 man-made isotopes of bismuth.

Finding the number of Protons, Neutrons, and Electrons
The atomic number is the number of protons in the nucleus. The number of electrons in a neutral atom equals the number of protons.

The number of neutrons is the difference between the mass number and the atomic number. neutrons = A - Z

Look at the periodic table and find the element by using the symbol. Z = 92 protons = 92 electrons = 92 A = 235 protons + neutrons = 235

How many neutrons are in a U-235 atom? Z = 92 protons = 92 electrons = 92 A = 235 protons + neutrons = 235

How many neutrons are in a U-235 atom? Z = 92 protons = 92 electrons = 92 235 – 92 = 143 neutrons

Q. Find the number of neutrons in the Ba-137 isotope.
Finding the number of Protons, Neutrons, and Electrons Q. Find the number of neutrons in the Ba-137 isotope. In the Ba-137 isotope … … Z = 56 and A = 137 137 – 56 = 81 neutrons

Copy the following table on notebook paper, and fill in the blanks.
Finding the number of Protons, Neutrons, and Electrons Copy the following table on notebook paper, and fill in the blanks.

Element Symbol Z A #p #n #e Zinc 66 In 68 85 38 82 210 Rn 136 35 47
Finding the number of Protons, Neutrons, and Electrons Element Symbol Z A #p #n #e Zinc 66 In 68 85 38 82 210 Rn 136 35 47

Complete the table, then go on.
Finding the number of Protons, Neutrons, and Electrons Stop! Complete the table, then go on. Element Symbol Z A #p #n #e Zinc 66 In 68 85 38 82 210 Rn 136 35 47

Element Symbol Z A #p #n #e Zinc 66 In 68 85 38 82 210 Rn 136 35 47
Finding the number of Protons, Neutrons, and Electrons Element Symbol Z A #p #n #e Zinc 66 In 68 85 38 82 210 Rn 136 35 47

Element Symbol Z A #p #n #e Zinc Zn 30 66 36 In 68 85 38 82 210 Rn 136
Finding the number of Protons, Neutrons, and Electrons Element Symbol Z A #p #n #e Zinc Zn 30 66 36 In 68 85 38 82 210 Rn 136 35 47

Element Symbol Z A #p #n #e Zinc Zn 30 66 36 Indium In 49 117 68 85 38
Finding the number of Protons, Neutrons, and Electrons Element Symbol Z A #p #n #e Zinc Zn 30 66 36 Indium In 49 117 68 85 38 82 210 Rn 136 35 47

Element Symbol Z A #p #n #e Zinc Zn 30 66 36 Indium In 49 117 68
Finding the number of Protons, Neutrons, and Electrons Element Symbol Z A #p #n #e Zinc Zn 30 66 36 Indium In 49 117 68 Strontium Sr 38 85 47 82 210 Rn 136 35

Finding the number of Protons, Neutrons, and Electrons Element Symbol Z A #p #n #e Zinc Zn 30 66 36 Indium In 49 117 68 Strontium Sr 38 85 47 Lead Pb 82 210 128 Rn 136 35

Finding the number of Protons, Neutrons, and Electrons Element Symbol Z A #p #n #e Zinc Zn 30 66 36 Indium In 49 117 68 Strontium Sr 38 85 47 Lead Pb 82 210 128 Radon Rn 86 222 136 35

Finding the number of Protons, Neutrons, and Electrons Element Symbol Z A #p #n #e Zinc Zn 30 66 36 Indium In 49 117 68 Strontium Sr 38 85 47 Lead Pb 82 210 128 Radon Rn 86 222 136 Bromine Br 35

Atomic mass is the weighted average of all the isotopes of an element
Boron has two isotopes: B % amu B % amu 0.198 x x = 10.81 amu

Determine the atomic mass of silicon: Si % amu Si % amu Si % amu x x x = amu

Consider the two isotopes of chlorine. Which isotope is more abundant? Cl - 35 ??.?? % amu Cl - 37 ??.?? % amu The average atomic mass is amu.

Consider the two isotopes of chlorine. Which isotope is more abundant? Cl % amu Cl % amu The average atomic mass is amu.

Which isotope of neon is more abundant? Ne-20 or Ne-22 Ne-20 90% Ne-22 10%

How are isotopes of the same element alike and different?
Number of protons and electrons Atomic number Chemical properties Different: Number of neutrons Mass Number Atomic mass of the isotopes

Which of the following is the same for the three isotopes of magnesium?
The atomic number of 12 The number of protons and electrons The number of neutrons The atomic weight of AMU The reaction with hydrochloric acid The speed of gaseous Mg atoms

All three isotopes of magnesium have the same atomic number.
Which of the following is the same for the three isotopes of magnesium? The atomic number of 12 Same All three isotopes of magnesium have the same atomic number.

2. The number of protons and electrons Same All isotopes of the same element have the same number of protons in the nucleus, and electrons outside the nucleus.

3. The number of neutrons Not the same The number of neutrons varies with the isotope. Different isotopes have different numbers of neutrons.

Not the same Mg-24  23.985 AMU Mg-25  24.986 AMU Mg-26  25.983 AMU
Which of the following is the same for the three isotopes of magnesium? 4. Atomic weight of AMU Not the same Mg-24  AMU Mg-25  AMU Mg-26  AMU

All isotopes of the same element react the same chemically.
Which of the following is the same for the three isotopes of magnesium? 5. The reaction with HCl Same All isotopes of the same element react the same chemically. The number and arrangement of electrons is the same for each isotope.

The speeds of atoms depend on mass.
Which of the following is the same for the three isotopes of magnesium? 6. The speed of gaseous Mg atoms Not the same The speeds of atoms depend on mass. Heavier atoms move more slowly, and lighter atoms move faster.

How did knowing about Graham’s Law allow the United States to win World War II?

Who were the two guys responsible for winning World War II?
Fat Man, and … Little Boy Atomic bombs dropped on Hiroshima and Nagasaki

Hiroshima

Nagasaki

Manhattan Project Oak Ridge, TN Graham’s law Gaseous diffusion Enriched uranium

Manhattan Project

Manhattan Project Naturally occurring uranium is mostly U-238 Less than 1% of naturally occurring uranium is U-235

Manhattan Project To sustain a nuclear chain reaction, uranium must be at least 4% U-235. Bomb grade uranium is over 90% U-235

Manhattan Project The uranium for a nuclear reactor is around 4% U-235. The process of increasing the percentage of U-235 is called enrichment.

Manhattan Project Uranium ore is reacted with fluorine to make gaseous UF6. Then the gaseous UF6 is introduced into chambers with porous disks in the ends.

Manhattan Project The lighter UF6 molecules containing U-235 effuse through the holes in the disk faster. There is more U-235 on the other side of disk.

Manhattan Project As the UF6 continues to move through many, many disks, the percentage of U-235 atoms in the gas increases, resulting in enrichment.

Manhattan Project Graham’s Law says that gas molecules which weigh less, will move faster than molecules which weigh more.

Manhattan Project The enriched UF6 containing a much higher percentage of U-235 atoms, is reacted with water to make uranium oxide and HF. The uranium oxide is dried and made into fuel pellets.

Uranium Pellet Fuel rod assembly

Only one element has unique names for its isotopes …
Deuterium and tritium are used in nuclear reactors and fusion research.

Some isotopes are radioactive
Radioactive isotopes are called radioisotopes. Radioisotopes can emit alpha, beta or gamma radiation as they decay.

Man-made Isotopes Man-made isotopes are usually made by bombarding atoms with protons or neutrons. Cobalt-59 occurs naturally. When a neutron “sticks” to the nucleus, cobalt-60 is formed.

Uses for Isotopes Radioisotopes are used to kill cancer cells. (Co-60, Bi-212) Radioisotopes are used in “imaging” living and nonliving systems. Radioisotopes are used as tracers in chemical reactions.

Half life

What is half life? Half life is the time needed for one half of a radioisotope to decay. Suppose you start with grams of a radioisotope that has a half life of exactly 1 year.

What is half life? How much will be left after 1 year?
Suppose you start with grams of a radioisotope that has a half life of exactly 1 year.

What is half life? After one year there will be 50.0 g left.
After a second year there will be 25.0 g left. Suppose you start with grams of a radioisotope that has a half life of exactly 1 year.

What is half life? After one year there will be 50.0 g left.
After a second year there will be 25.0 g left. After a third year there will be 12.5 grams left. After a fourth year there will be 6.25 grams left.

Half life project Pick a mass between 10g and 50g.
Decide on a half life – any time. Scale your graph – mass on y-axis and at least six (6) half-lives on the x-axis. Plot the masses after intervals of one half-life.

Half life project What shape is the graph?
When will the mass of the radioisotope fall to zero? When is the radioactivity no longer a problem? What mathematical function describes radioactive decay?

Half life project mass time 10 5 2.5 t1/2 t1/2 t1/2

Half life project A = A0e-kt 10 Exponential decay 5
Activity (counts/min) 2.5 t1/2 t1/2 t1/2 time

Half life project 10 Radiation is “not a problem” when it falls below background level. 5 Activity (counts/min) background 2.5 t1/2 t1/2 t1/2 time

Half life project 400 years Questions:
1. A radioisotope has a half-life of 100 years. How long will it take for the radiation to decrease to 1/16 of its original value? 400 years

Half life project 4 hours Questions:
2. A radioisotope has an activity of 560 counts per minute. After 16 hours the count rate has dropped to 35 counts per minute. What is the half life of the radioisotope? 4 hours

Decay equations

Alpha decay In alpha decay, an alpha particle (2He4) is released from the nucleus. The alpha particle carries away two protons and two neutrons.

Alpha decay decay product 92U238  2He4 + 90Th234 alpha particle

Alpha decay 92U238  2He4 + 90Th234 The mass number decreases by 4.
The atomic number decreases by 2.

Alpha decay 92U238  2He4 + 90Th234 These must add up to 238

Alpha decay Radon-220 decays by alpha emission. What is the decay product? 86Rn220  2He ??? 84Po216

Alpha decay 2He4 + 93Np237 95Am241  2He4 + 82Pb212 84Po216 
Write the alpha decay equations for: 2He Np237 2He Pb212 2He Rn222 95Am241  84Po216  88Ra226 

Beta decay Beta decay occurs because of the instability of a neutron.
Neutrons are a little more massive than protons; neutrons are neutral. What does this suggest about the composition of neutrons?

Beta decay Scientists used to think that neutrons might be a combination of a proton and an electron. We know that neutrons decay into protons, which stay in the nucleus, and electrons, which are ejected from the nucleus as beta particles.

Beta decay The conversion of a neutron to a proton involves the “weak” force. An “up” quark flips to become a “down” quark. When this occurs a high energy electron (beta) and an antineutrino are produced, both of which leave the nucleus.

Beta decay Decay of a neutron: 0n1  1H e0 neutron proton electron The electron ejected from the nucleus is a beta particle.

Beta decay Technically, the decay of a neutron also involves a neutrino. 0n1  1H e n0 neutron proton electron antineutrino

Beta decay 0n1  1H1 + -1e0 + 0n0 Actually, an anti-neutrino. neutron
The word “neutrino” comes from Enrico Fermi, meaning “little neutral one” in Italian. 0n1  1H e n0 neutron proton electron antineutrino

Beta decay A neutrino is a particle with no charge and almost no mass. 0n1  1H e n0 neutron proton electron antineutrino

Beta decay A neutrino carries off some of the energy in the decay of the neutron. 0n1  1H e n0 neutron proton electron antineutrino

Beta decay When predicting the products of beta decay we will ignore neutrinos. 0n1  1H e n0 neutron proton electron antineutrino

Beta decay Suddenly a neutron decays! Start with a Li atom with
3 protons and 4 neutrons. Beta decay Suddenly a neutron decays! Now there are 4 protons and 3 neutrons. A beta particle goes zipping out of the nucleus.

Beta decay A neutron decays to make a proton. The number of neutrons
The number of protons The mass number The atomic number decreases by 1 increases by 1 stays the same.

Beta decay decay product 6C14  7N e0 beta particle

Beta decay 6C14  7N14 + -1e0 The mass number stays the same.
The atomic number increases by 1.

Beta decay 6C14  7N14 + -1e0 These add up to 14
Notice that these add up to 6

Beta decay Zn-69 decays by beta emission. What is the decay product? 30Zn69  -1e ??? 31Ga69

Beta decay -1e0 + 83Bi214 -1e0 + 28Ni62 82Pb214  27Co62 
Write the beta decay equations for: -1e Bi214 -1e0 + 28Ni62 82Pb214  27Co62  3. ???  -1e0 + 48Cd113 47Ag113

Gamma rays Gamma radiation is often emitted along with alpha and beta radiation. When a decay event occurs, “extra” energy is sometimes left in the nucleus.

Gamma rays The “extra” energy in the decay product is released as gamma radiation. This lowers the energy of the nucleus and makes it more stable.

Review: decay equations
Alpha: Go down two on periodic table Atomic number decreases by 2 Mass number decreases by 4 Beta: Go up one on periodic table Atomic number increases by 1 Mass number stays the same

What holds the nucleus together?

Did you ever wonder ... Why the nucleus stays together with all those positively charged protons in such a small space? Protons have a positive charge and objects with like charges repel each other.

Why do they look like this?
Each hair has the same charge.

Did you ever wonder ... Because of the electrostatic repulsion…
…the nucleus shouldn’t even exist!

Did you ever wonder ... The strong force.
There must be a force that is stronger than the electrostatic repulsion. The strong force.

Did you ever wonder ... The strong force is the force that holds the quarks together to make protons and neutrons. The residual strong force extends from the quarks in a proton or neutron to the quarks in an adjacent proton or neutron and holds the nucleus together.

There is a closely related mystery.

Here’s a mystery Consider the iron-56 isotope.
It has a mass of amu. How many protons, neutrons and electrons? 26 protons 30 neutrons 26 electrons

Here’s a mystery But! Protons: 26 x 1.0073 = 26.189
Calculate the mass of the Fe-56 atom in amu from the sum of the parts: Protons: 26 x = Neutrons: 30 x = Electrons: 26 x = Total mass = But! The actual mass is

Here’s a mystery The actual mass of an isotope can be found using a device called a mass spectrometer. The actual mass is

magnetic field Mass spectrometer
magnetic field Mass spectrometer

Magnetic field makes charged atoms curve.
magnetic field Magnetic field makes charged atoms curve.

Here’s a mystery The sum of the protons, neutrons and electrons is amu. but, The actual mass is amu. – = amu

Here’s a mystery – = amu Sum of parts: p+, n, e- actual isotope mass ? Where is the missing mass?

Recall Einstein’s famous equation:
The solution Recall Einstein’s famous equation: E = mc2 What does it tell us? Matter and energy are equivalent.

The solution Matter can exist as energy and …
… energy can exist as matter. They are both the same “thing”. All calculated from E = mc2

The solution The difference between the mass of the parts (p+, n and e-) and the actual mass is called the “mass defect” and equals the mass of nuclear material that “exists as energy”.

The solution The energy from the missing mass is the binding energy of the nucleus. The binding energy is derived from the strong force which does hold the nucleus together.

The solution The binding energy is the energy required to “take apart” the nucleus to form nothing but individual protons and neutrons.

Is this binding energy related to nuclear energy?

Nuclear energy All nuclear decay is accompanied by a release of energy. Alpha and beta particles have high kinetic energies. Gamma rays are electromagnetic energy. All have enough energy to ionize atoms.

cancer Nuclear energy An ion is a “charged atom” or group of atoms.
Ionization occurs when electrons are removed from atoms by a, b or g radiation. cancer This can result in damage to your body.

Nuclear energy Forms of ionizing radiation are: Alpha Beta Gamma
X-rays Cosmic rays Neutrons Positrons Ultraviolet light (UV) can cause cancer, but it is not ionizing radiation.

There’s even more! Some of the energy that holds the nucleus together is carried away by the alpha, beta and gamma radiation. But there is an even greater release of energy when the atom splits apart …

Nuclear Fission

Nuclear fission Fission – the splitting of an atom after the nucleus absorbs a neutron.

Nuclear fission A neutron collides with a nucleus and is absorbed.
The mass number of the atom increases and the nucleus becomes unstable.

Nuclear fission The unstable nucleus splits into two or more fission fragments. Plus, two or three neutrons are released along with a great deal of energy. The neutrons strike other atoms causing more fission.

Nuclear fission Neutrons Fission fragment U-235 Neutron

Nuclear fission U-235 Neutrons Fission fragment These U-235 atoms can split when hit by neutrons, and release more neutrons, starting a chain reaction.

Nuclear fission To picture a chain reaction, imagine 50 mousetraps in a wire cage. And on each mousetrap are two ping-pong balls. Now imagine dropping one more ping-pong ball into the cage …

Detail of ping-pong balls on mousetraps.

http://www. physics. montana

Nuclear fission As the chain reaction proceeds, energy is released as heat energy. This energy originally held the nucleus together. Billions of splitting atoms releases a huge amount of heat energy.

Nuclear fission This heat energy can be harnessed to boil water,
creating steam, that can spin a turbine, that can turn a generator, creating electricity.

Nuclear reactor

Nuclear reactor Containment building Reactor core Fuel rods
Heat exchanger Steam generator Steam to turbine Fuel rods Water from cooling lake Water circulates in the core

Nuclear reactor Containment building
Cadmium control rods – absorb neutrons Reactor core Steam to turbine Fuel rods Water from cooling lake Water circulates in the core

Nuclear reactor Containment building The water in the core
serves two functions. (1) The water cools the core and carries away heat. (2) Water is a moderator. The water slows the neutrons so that they can cause fission. Fast neutrons do not cause fission. Nuclear reactor Reactor core Steam to turbine Fuel rods Water from cooling lake Water circulates in the core

Water from cooling lake Water circulates in the core

Heat exchanger Steam generator Fuel rods Water from cooling lake Water circulates in the core

Heat exchanger Steam generator Steam to turbine Fuel rods Water from cooling lake Water circulates in the core

From nuclear energy to…
Heat exchanger Steam generator Transmission wires turbine generator Steam to turbine Condensed steam Water from cooling lake Cooling towers or lake

Electrical energy Heat exchanger Steam generator Transmission wires
turbine generator Steam to turbine Condensed steam Water from cooling lake Cooling towers or lake

Electrical energy This part of the system is the same regardless of how the steam is produced. The heat can come from nuclear energy or by burning coal, natural gas or fuel oil. Heat exchanger Steam generator Transmission wires turbine generator Steam to turbine Condensed steam Water from cooling lake Cooling towers or lake

Electrical energy In fact, the only purpose of a nuclear reactor
is to boil water.

Pros and cons Cheap, plentiful power, no CO2, nuclear waste, terrorist attack, running out of oil and coal, on-site storage, breeder reactors, transportation of spent fuel, “not in my backyard”, …

What about fusion?

Nuclear fusion A day without sunshine is like a day without fusion.

Nuclear fusion Nuclear fusion powers the sun.
Fusion occurs when hydrogen atoms combine to make helium, and release energy. Is nuclear fusion an alternative to fission for producing electricity?

Nuclear fusion Fusion not now technically feasible.
Occurs at very high temperatures which nothing can withstand. Magnetic bottle. Control problems. Now consumes more energy than it releases.

Developed by Mike Jones
Nuclear Chemistry Developed by Mike Jones Pisgah High School Canton, NC

Nuclear Chemistry M. Jones Pisgah High School Last revision: 100211.

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