Pearson Prentice Hall Physical Science: Concepts in Action Chapter 10 Nuclear Chemistry

10.1 Radioactivity Objectives: 1. Describe the process of nuclear decay 2. Classify nuclear radiation as alpha particles, beta particles or gamma rays 3. Balance nuclear equations 4. Identify sources of nuclear radiation and describe how nuclear radiation affects matter 5. Describe methods of detecting nuclear radiation

The Process of Nuclear Decay Definition: radioactivity is the process in which an unstable atomic nucleus emits charged particles and energy Definition: a radioisotope is any atom containing un unstable nucleus During nuclear decay, atoms of one element can change into atoms of a different element altogether

Types of Nuclear Radiation Definition: an alpha particle is a positively charged particle made up of two protons and two neutrons (the same as a helium nucleus) In alpha decay the product isotope has two fewer protons & two fewer neutrons than the reactant isotope Definition: a beta particle is an electron emitted by an unstable nucleus In beta decay the product isotope has one proton more and one neutron fewer than the reactant isotope

Gamma Rays Definition: a gamma ray is a penetrating ray of energy emitted by an unstable nucleus Gamma radiation has no mass and no charge During gamma decay the atomic number & mass number remain the same, but the energy of the nucleus decreases Gamma radiation is very penetrating compared to the alpha and beta

Balance Nuclear Equations

Sources &Effects of Nuclear Radiation Definition: background radiation (also called naturally occurring nuclear radiation) occurs naturally in the environment When nuclear radiation exceeds background levels, it can damage cells and tissues Nuclear radiation can ionize atoms including alpha, beta and gamma Alpha can burn skin but is not serious unless inhaled or eaten (ex: radon gas in homes) Beta does more damage than alpha, but less than gamma Gamma rays cause extensive damage

Detecting Nuclear Radiation Devices that are used to detect nuclear radiation include geiger counters & film badges Film badges are worn by people who work with radiation to detect excessive levels

10.2 Rates of Nuclear Decay Objectives: 1. Define half-life and relate half- life to the age of radioactive isotope 2. Compare and contrast nuclear reaction rates with chemical reaction rates 3. Describe how radioisotopes are used to estimate the age of materials

Half-Life & Rates of decay Definition: half-life is the time required for one half of a sample of a radioisotope to decay Half life = total time of decay/half-life Q: If a radioactive sample has decayed until one eighth of the original sample remains, how many HL have elapsed? A: three HL ( ½ x ½ x ½ = 1/8 ) Nuclear decay rates are constant regardless of temperature, pressure or surface area of the reactant (ex: uranium-238) Chemical reactions are affected by local conditions (temp, press, surface area, etc.)

Estimating Age Carbon-14 has an unstable nucleus and is radioactive It can be used to determine the age of an object by comparing the object’s carbon-14 levels with the carbon-14 levels in the atmosphere 146C --> 147N + 0-1e (half-life is 5720 years) Any object can be dated that is less than 50,000 years old Older objects contain too little carbon to be useful

10.3 & 10.4 Fission and Fusion Objectives: 1. Explain what a particle accelerator is 2. Describe the process of nuclear fission 3. Explain how nuclear reactors are used to produce energy 4. Describe the process of nuclear fusion

Particle Accelerators Definition: transmutation is conversion of atoms of one element into atoms of another element Scientists can bombard atomic nuclei with high energy protons, neutrons or alpha particles creating a new element The equipment used to do this is called a particle accelerator An important accelerator is located in Illinois

Nuclear Fission Definition: fission is the splitting of an atomic nucleus into two smaller parts Tremendous amounts of energy can be produced from very small amounts of mass by creating a chain reaction Definition: a chain reaction produces a series of nuclear reactions by releasing neutrons off an initial nuclear trigger Speed of the reaction can vary Controlled reactions can be used to produce electricity

The Process of Fission Definition: critical mass is the smallest possible mass of fissionable material that can sustain a chain reaction The fissionable material in the United States is radioactive uranium-235 Electricity production with controlled fission takes place at nuclear power plants There are not many out West, although some politicians are trying to change that Currently, the majority of nuclear power plants are located East of Nevada

Using Nuclear Reactors Nuclear power plants do not emit air pollutants unlike power plants that burn fossil fuels Workers in nuclear plants must wear protective clothing reducing exposure to radiation The uranium-235 produces many radioactive isotopes The waste must be stored for hundreds of half-lives or thousands of years

The waste must be isolated from humans & the environment Operators have lost control of the reactor from time to time During a nuclear core meltdown the core melts and radioactive material can be released A partial meltdown happened in 1986 in Chernobyl, Ukraine Chernobyl will be uninhabitable for many generations to come It came to close to happening at Three Mile Island, Pennsylvania

Fusion Definition: fusion is the process in which the nuclei of two atoms combine to form a larger nucleus A fraction of the reactant is converted to energy during this process but we do not yet have the technology to harness the energy & convert it to electricity Fusion requires the temperature of the sun in excess of 10 million degrees Definition: plasma is a state of matter in which atoms have been stripped of their electrons Fusion reactors do not yet exist due to the temperatures required to start the reaction & they must contain plasma