nuclear chemistry. section 1: basic definitions nuclear chemistry – the study of the atomic...
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Nuclear Chemistry
Section 1: Basic Definitions
• Nuclear Chemistry– The study of the atomic nucleus, its reactions and
radioactivity• Radioactivity– Spontaneous emission of particles and/or energy
during nuclear decay
Section 1, continued
• Nuclear Decay– Spontaneous disintegration of a nucleus– Results in a new element being formed– Occurs when particles and/or energy escape from
an unstable nucleus– Releases large amounts of energy
• Radiation– Can refer to either the particles or energy released
during nuclear decay
Section 2: Types of Radiation to Know
Radiation Description• Proton
– Positively charged particle in the nucleus of the atom
– Hydrogen nucleus– Most cosmic rays are protons traveling at
the speed of light
• Neutron– Neutral particle in the nucleus of the atom
• Electron (Beta-minus particle)– Negatively charged particle that moves
randomly in specific orbitals outside the nucleus of an atom
Radiation Symbol
• Proton:
• Neutron: n
• Electron: e, β-
Section 2, continued
Radiation Description• Positron (Beta-positive particle)
– Anti-matter electron– Same properties of an electron
except it has a positive charge
• Alpha Particle– Helium nucleus– 1st radioactive particle discovered by
Ernest Rutherford
• Gamma Radiation– High energy electromagnetic
radiation
Radiation Symbol• Positron: e, β+
• Alpha: He, α
• Gamma: γ
Section 3: Properties of Certain Types of Radiation
Property Alpha Particle Beta-minus particle
Beta-positive particle
Gamma Radiation
Charge
+2 -1 +1 n/a
Speed
Largest and slowest form of radiation
Faster than alpha
Faster than alpha (same as beta-minus)
Speed of light
Can be stopped by…
Piece of paper Plastic, aluminum foil
Plastic, aluminum foil
Thick lead or concrete
Section 4: Isotopes
• Same element, different number of neutrons• There are 2 ways to identify isotopes:– Hyphen-Notation = element – mass #• Example: oxygen – 16
– Chemical Configuration• Example:
charge ionicnumber mass
number atomic
-216 8 O
Section 4, continued
• Isotopes of hydrogen have special names
• Deuterium and tritium are radioactive; protium is not.
Section 4, continued
• Why are some isotopes radioactive and others are not?– The proton : neutron ratio determines whether an isotope is
radioactive• Elements with atomic # ≤ 20 prefer a 1 : 1 ratio• Elements with atomic # > 20 prefer a 1 : 1.5 ratio
• Transuranium elements = – Elements with atomic # > uranium (92)– All are radioactive– In fact, all elements with atomic number > 83 are
radioactive!
Section 4 Example Problems
1. Write the hyphen-notation and the chemical configuration for an iron atom that has 23 electrons and 32 neutrons.
Section 4 Example Problems, continued
2. Write the hyphen-notation and determine the number of protons, neutrons and electrons for P.
Section 4 Example Problems, continued
3. Write the hyphen-notation and chemical configuration for the three isotopes of hydrogen. Assume each isotope is neutral.
Section 5: Use of Carbon-14 in Radiocarbon Dating
Section 6: Nuclear Reactions v Chemical Reactions
Nuclear Reactions• Forms a new isotope or
different element• Extremely large energy
changes• Energy comes from the
binding energy of the nucleus
• Involves a change in the number of protons or neutrons
Chemical Reactions• Forms new substances
based on the elements present in the reactants
• Small energy changes• Energy comes from
breaking and forming chemical bonds
• Involves valence electrons
Section 7: Writing Nuclear Reactions
Steps1. Set up 2 equations: one
using the mass (top) numbers and the other using the atomic (bottom) numbers.
2. Calculate the missing mass number.
3. Calculate the missing atomic number.
4. Use the atomic/mass #s to determine the identity of the missing particle.
Example
+ _________ Mass #s: 29 = 0 + _____
Atomic #s: 12 = -1 + _____
Section 8: Alpha Emission
• A helium nucleus (2 p, 2 n) is emitted from the nucleus
• Example: Alpha decay of 241Am
Section 8: Beta Emission
• A neutron is converted into a proton and electron, then the electron (β- particle) is emitted
• Example: Beta decay of 14C
Section 8: Positron Emission• A proton is converted into a neutron and
positron, and the positron is emitted from the nucleus
• Example: Positron Emission of 11C
Section 8: Electron Capture
• The nucleus captures an electron and combines it with a proton to form a neutron
• Example: Electron capture by 7Be
Section 8: Gamma Emission
• Gamma rays are emitted during nuclear reactions, either alone or with other types of radiation
• Gamma rays do NOT change the mass number or atomic number because they are energy not matter. Pu* Pu
γ ray
Section 9: Decay SeriesA series of nuclear reactions that occur until a stable nucleus is formed
The first 4 nuclear reactions in the uranium-238 decay series are:
238U 42He + 234Th
234Th 0
-1β + 234Pa
234Pa 0
-1β + 234U
234U 4
2He + 230Th
Section 10: Fission
• Definition– heavier nuclei split apart to form lighter nuclei
• Occurs in…– Nuclear power plants, nuclear bombs
• Chain Reaction (definition)– neutrons produced from one reaction can hit
other isotopes to start a new fission reaction• Example of Fission Reaction
+ + + 3
Section 11: Nuclear Power PlantContainment Structure (A)-thick layers of concrete and steel to prevent radiation leakageControl Rods (B)-controls the rate of reaction; can be used to shut reaction downReactor (C)-where the nuclear reactions take placeSteam Generator (D)-nuclear reactions produce heat energy which is used to boil waterTurbine (H)-steam runs the turbine, which causes the generator (G) to produce electricityFuel Rods (K)-usually contain uranium-235; the fuel for the nuclear fission reaction Condenser (I)-sends cool water to the cooling tower (J) and reactor; vital to keep reactor from overheating
Section 11: Nuclear Power Plant
• A nuclear reactor is self-sustaining due to the chain reaction. The neutrons that are produced from one reaction cause a new fission reaction to occur.
Section 12: Nuclear Power (Fission) Pros and Cons
Pros• No air pollution• No greenhouse gas
emissions• Low cost fuel because very
little is needed• Can be done at room
temperature
Cons• Expensive to build and
maintain• Risk of accidents• Security• Thermal pollution (warm
water into streams and rivers)
• Disposal of nuclear waste (must be buried for possibly thousands of years)
Section 13: Fusion Reaction
• Definition– light nuclei combine (fuse) together to form
heavier nuclei• Occurs in…– the sun and other stars; hydrogen (fusion) bomb
• Example of Fusion Reaction + +
Section 14: Fusion Pros and Cons
Pros• Produces even more energy
per gram of fuel than fission.
• Produces less nuclear waste than fission.
• Fusion fuel is easy to get. (Heavy hydrogen is found in water.)
Cons• Does not sustain a chain
reaction.• Requires extremely high
temperatures (108 - 109 °C) and pressures.
• We do not have the technology to efficiently harness the energy produced by fusion or to contain a fusion reaction.