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.