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Nuclear Chemistry.

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Presentation on theme: "Nuclear Chemistry."— Presentation transcript:

1 Nuclear Chemistry

2 Remember the easy stuff!!
nucleus Electrons We don’t care about the electrons right now…

3 What particles make up the nucleus?
Both protons and neutrons are called NUCLEONS protons neutrons

4 238U 92 Recall some stuff about the nucleus: Mass number Notation:
element Atomic number Isotopes: nuclei with the same number of protons, but not necessarily the same number of neutrons

5 Isotopes Isotopes have the same number of protons, different number of neutrons Another way to show an isotope is to have the mass number follow the name of the element (Carbon-14)

6 (c) number of electrons in orbit around the nucleus.
12C and 13C differ in their (a) number of neutrons. (b) number of protons. (c) number of electrons in orbit around the nucleus. (d) chemical behavior. (e) all of the above.

7 What is the charge on a proton? The neutron?
What is the nature of the force between the nucleons? How does the nucleus hold itself together??!!

8 The Nucleus is a delicate balance between
[1] The attractive nuclear strong force between all of the nucleons, and [2] The repulsive electromagnetic force between all of the protons

9 It turns out that our delicate balance of forces tends to break down when nuclei get large:
The electromagnetic forces eventually overcome the nuclear ones and the nucleus spontaneously breaks apart

10 This “instability” is called radioactivity:
All nuclei having atomic number larger than 83 (bismuth) are radioactive.

11 Radioactivity Radioactivity is the process in which an unstable atomic nucleus emits charged particles and energy Any atom containing an unstable nucleus is called a radioactive isotope or radioisotope for short

12 As more protons are added (the nucleus gets heavier) the proton-proton repulsion gets larger.
The heavier the nucleus, the more neutrons are required for stability. The belt of stability deviates from a 1:1 neutron to proton ratio for high atomic mass.

13 Ratio of neutrons to protons in nucleus determines if nuclei are stable
Too many neutrons Too few neutrons nuclei with >than 83 protons all unstable

14 Radioactive decay is how nuclei get to belt of stability

15 sometimes an unstable nucleus goes through a series of nuclear reactions before it gains stability. This sequence is called a radioactive series

16 3 Types of Spontaneous Decay: 1. Alpha particle emission
2. Beta particle emission 3. Gamma ray emission High energy photon (light)

17 A little bit of History

18 Florescent Screen Lead block Uranium Gold Foil Remember this?

19 This led to the discovery of the nucleus…

20 Ernest Rutherford’s Other Experiment:

21 No study on radiation is complete without giving credit to the Curies (Marie, Pierre and Irene)-
Their discoveries include radium, polonium and positron. Marie-died from Overexposure To radiation

22 Types of Nuclear Radiation
Alpha 2.Beta 3. Gamma

23 alpha particles and alpha decay
alpha particles and alpha decay

24 What is an alpha-particle?
It has two protons and two neutrons 4He 2

25 What is alpha-decay? It is when a nucleus emits an alpha particle 4He 2 Alpha Decay = Alpha Particle Emission

26 Nuclear Equations -represent nuclear decay to become stable - they must balance.
1) mass # 2)atomic # The total number of p+and n0 before a nuclear reaction must be the same as the total number of nucleons after reaction.

27 1. Alpha emission Nuclides that undergo alpha decay have too many protons for stability ( >83 protons and mass > 209 )


29 Alpha Particles (a)- They have a mass of 4 and charge of +2
Remember: This is the mass number, which is the number of protons plus neutrons Alpha Particles (a)- They have a mass of 4 and charge of +2 Radium Ra226 88 Radon Rn222 86 + p n n p a (4He) 88 protons 138 neutrons 86 protons 136 neutrons 2 protons 2 neutrons The alpha-particle (a) is a Helium nucleus. It’s the same as the element Helium, with the electrons stripped off ! The alpha particles go in the air collide with air molecules and become Helium – not dangerous.

30 Example: Write the nuclear equation for the alpha decay of uranium 238:
92 234X 90 + Now look at the chart to find this one: THORIUM

31 Nuclear Equation Practice: Alpha Decay
How would alpha decay equations be written for these atoms: U  Po 

32 beta particles and beta decay
beta particles and beta decay

33 Beta Decay Electron! 14C 6 14N 7 + electron (beta)

34 2.Beta emission A neutron turns into a proton and an electron.
200link 2.Beta emission A neutron turns into a proton and an electron. The beta particle is the electron, written as e or 


36 Beta Particles (b)- are electrons, “no” mass and charge of –1
Beta Particles (b)- are electrons, “no” mass and charge of –1. The decay of Carbon 14 Carbon C14 6 Nitrogen N14 7 e- + 0Electron -1 (beta-particle) 6 protons 8 neutrons 7 protons 7 neutrons We see that one of the neutrons from the C14 nucleus “converted” into a proton, and an electron was ejected. The remaining nucleus contains 7p and 7n, which is a nitrogen nucleus. In symbolic notation, the following process occurred: n  p + e

37 Write out the nuclear equations in each case and identify the daughter nuclei:
Alpha decay of Rn: Beta decay of 3H: Beta decay of 90Sr 86 1 38

38 A beta particle is an electron emitted by an unstable nucleus
Beta Decay A beta particle is an electron emitted by an unstable nucleus Beta particles can be stopped by a thin sheet of metal such as aluminum

39 Nuclear Reaction Equation Practice: Beta Decay
A beta particle is written 0-1 e or  During beta decay, the mass remains the same and the atomic number increases by one Pb  Po 

40 3890Sr is a radioactive isotope that decays by beta-decay
3890Sr is a radioactive isotope that decays by beta-decay. Its daughter nucleus is (a) 3686Kr. (b) 3788Rb. (c) 3789Rb. (d) 3989Y. (e) 3990Y.

41 gamma rays and gamma decay
gamma rays and gamma decay

42 Gamma decay occurs because the nucleus is at too high an energy
Gamma decay occurs because the nucleus is at too high an energy. The nucleus falls down to a lower energy state and, in the process, emits a high energy photon known as a gamma particle. Here's a diagram of gamma decay with helium-3: Gamma decay is only energy emission, not particle emission.

43 Gamma particles (g) In much the same way that electrons in atoms can be in an excited state, so can a nucleus. Neon Ne20 Neon Ne20 + 10 protons 10 neutrons (in excited state) 10 protons 10 neutrons (lowest energy state) gamma A gamma is a high energy light particle. It is NOT visible by your naked eye because it is not in the visible part of the EM spectrum. It has neither Charge nor mass. They are highly penetrating.

44 Gamma decay A gamma ray is a penetrating ray of energy emitted by an unstable nucleus Gamma rays are energy waves that travel through space at the speed of light

45 Gamma decay During gamma decay, the atomic number and mass remain the same, but the energy of the nucleus decreases Gamma rays can be stopped by several centimeters of lead or by several meters of concrete

46 There are other types of radioactive decay we will not go into:
- positron emission - neutron emission

47 Measuring Radiation

48 The unit of radiation exposure is called the
REM (Radiation Equivalent in Man) This is a direct measure of the number of damaged cells. The average dose for one year is about 0.3 Rem Sudden dose of 1000 rems causes death in 30 days!!

49 Exposure to ionizing radiation:
All of these are IONIZING RADIATION alpha beta gamma Ionizing radiation causes cell damage that can lead to DNA damage that can lead to CANCER.

50 Radiation Doses Normal 1 XRay (medical) 0.04 rem = 40 mrem
CAT Scan 3 rem Portland  New York 1 mrem (4 hr flight) (0.001 rem) Cosmic Rays 30 – 50 mrem/year Food (40K, Ra) ~40 mrem/year

51 Bad News (acute radiation exposures)
1 rem 25-50 rem rem 450 rem 1000 rem 5000 rem More cancer ~ 100 extra cases per 106 people ( chance) Lose white blood cells (+ above) Sick, low white blood cell count, Get Leukemia in years, Genetic mutations in progeny. 50% death in 30 days (with “heroic” medical intervention) Death, 100% Can’t shoot back

52 Detecting Radiation Devices used to detect radiation include Geiger counters and film badges

53 Penetrating Radiation
The penetrating power of radiation is really a function of mass. -radiation (zero mass) penetrates much further than -radiation, which penetrates much further than -radiation. When radiation penetrates the body most of its energy is absorbed by water molecules. Alpha, beta and gamma rays are all forms of ionizing radiation that can ionize water. Alpha rays are stopped by skin and beta rays can penetrate about 1 cm beyond the surface of the skin. Gamma rays are the most penetrating of the three types of radiation. Inside the body, alpha rays are the most dangerous form of radiation.


55 “Background” Radiation
Background radiation is nuclear radiation that occurs naturally in the environment Radioisotopes in the air, water, rocks, plants, and animals all contribute to background radiation Cosmic rays (streams of charged particles) from outer space that collide with the Earth’s atmosphere also contribute Background radiation levels are low enough to be safe

56 Half-Life

57 RATES OF NUCLEAR DECAY A half-life is the time required for one half of a sample of radioactive sample of a radioisotope to decay Unlike chemical reactions, nuclear decay rates are constant regardless of temperature, pressure or surface area

58 A very important concept in nuclear chemistry and its applications is the idea of
HALF-LIFE Half-Life: the TIME it takes for half of a given amount of a specific isotope to decay This depends on the relative stability of the the isotope in question: semi-stable nuclei last longer than very unstable ones.

59 1 Kg Example: 14C (half-life 6,000 years). How much is left after 6,000 years? 12,000 years? 18,000 years? 24,000 years? 30,000 years? 36,000 years?

60 1 Kg Example: 14C (half-life 6,000 years). There must be an easier way! How much is left after 6,000 years? 12,000 years? 18,000 years? We divided by 2 six times 24,000 years? 30,000 years? 36,000 years?


62 We can do the process in reverse to see how much time it took a substance to decay:
Radioactive Dating:

63 Applications

64 Let’s meet some of the unstable isotopes in our neighborhood:
Radon -222 Forms as part of the Uranium Series Decomposition of Uranium in many rocks-granite Migrates into basement cracks Dense and collects in lower part of house Readily inhaled Its decomposition product is polonium, if it decays in the lung it emits an alpha particle The polonium solid decays resulting in lung disease

65 Radium 226 1st radioactive element associated with biological damage Some are phosphorescent (glow) Believed to cause the reaction that caused leukemia that killed Marie Currie Uranium-238 Used to estimate age of earth We use its half life to estimated how long it has been since the rock solidified.

66 Potassium 40 Light element (one of the few) Emits positron to form Ar-40 Most of argon in atmosphere is Ar-40

67 Artificial Radioactive isotopes-Transmutation
Artificial radioactive Isotopes are produced by bombarding a target element with nuclei of other elements Carried out in cyclotron Many new and useful Isotopes have been created.


69 Practical uses of Radioisotopes
H-3 Tritium Archaeological dating Am Americium Smoke detectors Co Cobalt Cancer treatment Cr Chromium Determination of blood volume U Uranium Nuclear reactors and weapons U Uranium Archaeological dating

70 Artificial Radioactive isotopes may be used as tracer materials.
Example: We might like to know how phosphorus in fertilizers is used by plants. By incorporating a small amount of radioactive Phosphorus in the fertilizer, chemists can measure the time it takes for plants to utilize the Phosphorus. They also can track where the P goes.


72 Dating Archeological samples
Example: U-238 decays slowly through the uranium disintegration series to lead The half-life of this conversion is 4.5 X 109 years. To determine the age of a rock, we need to determine the amount of uranium present when the rock solidified, No and the amount of uranium in the rock today, Nf

73 The amount of U-238 present in the rock today can be measured
The amount of U-238 present in the rock today can be measured. However, we can’t calculate the original. The solution lies in the fact that each atom of uranium ends up as an atom of lead. Therefore, if we take a rock sample and determine the number of atoms of U-238 and the number of atoms of Pb-206, we can say that No = atoms U atoms Pb-206 Nt = atoms 238-U **Errors will exist, the original rock may have contained some Pb-206 and some of the original U-238 may not end up as Pb-206

74 Fusion & Fission

75 FISSION AND FUSION Fission is the splitting of an atomic nucleus into two smaller parts Fusion is a process in which the nuclei of two atoms combine to form a larger nucleus

76 Fission A chain reaction is a chain of fission reactions triggered by neutrons released during the fission of a nucleus About 20% of the electricity in the US comes from fission reactions

77 Fission A tremendous amount of energy is produced during a fission reaction

78 Fission Advantages to using fission reactions is the lack of air pollution. Disadvantages include the risk of exposure and radioactive waste

79 Nuclear Power Plant FG21_020.JPG
Enriched uranium pellets encased in Zr or stainless steel tubes are used for fuel in nuclear power plants. Control rods made of Cd or B control the fission process by absorbing neutrons. A moderator slows down the neutrons so they are more likely to be captured by the fuel. A cooling liquid circulates through the reactor and its heat is used to produce steam which generates electricity by driving a steam turbine.

80 2 subcritical masses come together when detonated
FG21_017.JPG Atomic Bomb 2 subcritical masses come together when detonated Chemical explosives are used to bring two subcritical masses of uranium-235 together to form a supercritical mass. A rapid, uncontrolled nuclear reaction results ultimately causing a nuclear explosion.

81 Fusion Fusion reactions can release huge amounts of energy Fusion reactions occur in the sun and stars

82 Nuclear Fission-the process that yields two nuclei of almost equivalent mass.
It does not occur spontaneously It is a chain reaction It is usually used to generate electricity. Heat is generated in fission reactions.

83 Nuclear Fusion- The combination of two nuclei into a larger atom is called nuclear fusion.
The reactions within the sun are fusion reactions that combine Hydrogen nuclei to form a helium atom It takes simple, nonradioactive materials and produces helium, so it should be a clean and inexpensive source of energy. Several designs for fusion reactors are being tested. Some success, it will be some time before this cheap, nonpolluting energy source will become a reality.

84 Nuclear fusion

85 Tokamak- uses magnetic fields to contain fusion rxn

86 Fusion of tritium and deuterium requires about 40,000,000K:
21H + 31H  42He + 10n These temperatures can be achieved in a nuclear bomb or a tokamak. A tokamak is a magnetic bottle: strong magnetic fields contained a high temperature plasma so the plasma does not come into contact with the walls. (No known material can survive the temperatures for fusion.) To date, about 3,000,000 K has been achieved in a tokamak.

87 Fusion reaction in sun provides all our energy makes smaller elements
fusion in supernova made elements larger than Fe

88 No attack involving nuclear weapons has occurred since.
Fat Man Produced this cloud after its detonation at Nagasaki on August 15th, 1945, killing at least 80,000 civilians instantly. 140,000 civilians perished in Hiroshima when Little Boy was dropped just two weeks earlier. No attack involving nuclear weapons has occurred since.

89 In 1961, when the USSR tested the Hydrogen Bomb “Tsar Bomba”, it was 4000 times more powerful than Little Boy. Its energy yield was ten times greater then all of the munitions exploded during all of World War 2. “A 50-mile radius of ground surface has been completely leveled, swept and licked so that it looks like a skating rink ... The same goes for rocks. There is not a trace of unevenness in the ground.... Everything in this area has been swept clean, scoured, melted and blown away." The shockwave destroyed buildings and tore roofs off of homes hundreds of miles from ground zero, and windows in Norway and Finland were shattered. From The USSR concluded that Tsar could not be safely deployed against Western European targets, since the radiation that would have been caused by the blast would spread to the Soviet border. The only cities that would be practical targets for such a device were the New York, Chicago, and Los Angeles metropolitan areas; the use of Tsar was considered overkill for any other target.

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