Review Atomic Number (Z) – number of protons Mass Number (A) – sum of protons and neutrons Copyright © Cengage Learning. All rights reserved

4 Forces in Nature Force Equation notes Gravity F = G m1 m2/r2 Works at an infinite distance. Weakest of all forces. Electromagnetic F = K q1 q2/r2 Works for short distances, Holds the atom together. Strong Nuclear force E =mc2 (mass defect) This is the glue that holds the nucleus together. Weak nuclear force The force responsible for radioactivity. Pulls the nucleus apart.

No nucleus beyond lead is stable indefinitely. Stable nuclei When the strong force is greater than the weak force the nucleus is stable. No nucleus beyond lead is stable indefinitely. Iron has the most stable nuclei. Most atoms have examples of stable and unstable nuclei

The Zone of Stability Copyright © Cengage Learning. All rights reserved

Unstable nuclei become stable by changing the make up of their nucleus When the weak force is greater than the strong force the nucleus is unstable. Unstable nuclei become stable by changing the make up of their nucleus This process is known as radioactive decay.

Radioactive Stability Nuclides with 84 or more protons are unstable. Light nuclides are stable when Z equals A – Z (neutron/proton ratio is 1). For heavier elements the neutron/proton ratio required for stability is greater than 1 and increases with Z. Copyright © Cengage Learning. All rights reserved

Radioactive Stability Certain combinations of protons and neutrons seem to confer special stability. Even numbers of protons and neutrons are more often stable than those with odd numbers. Copyright © Cengage Learning. All rights reserved

Radioactive Stability Certain specific numbers of protons or neutrons produce especially stable nuclides. 2, 8, 20, 28, 50, 82, and 126 Copyright © Cengage Learning. All rights reserved

Types of Radioactive Decay Alpha production (α): Beta production (β): Copyright © Cengage Learning. All rights reserved

Types of Radioactive Decay Gamma ray production (γ): Positron production: Copyright © Cengage Learning. All rights reserved

Types of Radioactive Decay Electron capture: Inner-orbital electron Copyright © Cengage Learning. All rights reserved

Decay Series (Series of Alpha and Beta Decays) Copyright © Cengage Learning. All rights reserved

Which of the following produces a particle? electron capture positron CONCEPT CHECK! Which of the following produces a particle? electron capture positron alpha particle beta particle The correct answer is d. Go through the rest of the equations to identify these types of equations as well. Copyright © Cengage Learning. All rights reserved

Rate of Decay Rate = kN The rate of decay is proportional to the number of nuclides. This represents a first-order process. Copyright © Cengage Learning. All rights reserved

Half-Life Time required for the number of nuclides to reach half the original value. Copyright © Cengage Learning. All rights reserved

Nuclear Particles To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE Copyright © Cengage Learning. All rights reserved

Half-Life of Nuclear Decay To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE Copyright © Cengage Learning. All rights reserved

EXERCISE! A first order reaction is 35% complete at the end of 55 minutes. What is the value of k? k = 7.8 × 10-3 min-1 k = 7.8 x 10-3 min-1. If students use [A] = 35 in the integrated rate law (instead of 65), they will get k = 1.9 x 10-2 min-1. Note: Use the red box animation to assist in explaining how to solve the problem.

Nuclear Transformation The change of one element into another. Copyright © Cengage Learning. All rights reserved

A Schematic Diagram of a Cyclotron

A Schematic Diagram of a Linear Accelerator Copyright © Cengage Learning. All rights reserved

Measuring Radioactivity Levels Geiger counter Scintillation counter Copyright © Cengage Learning. All rights reserved

Geiger Counter To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE Copyright © Cengage Learning. All rights reserved

Carbon–14 Dating Used to date wood and cloth artifacts. Based on carbon–14 to carbon–12 ratio. Copyright © Cengage Learning. All rights reserved

Radiotracers Radioactive nuclides that are introduced into organisms in food or drugs and whose pathways can be traced by monitoring their radioactivity. Copyright © Cengage Learning. All rights reserved

Radiotracers Copyright © Cengage Learning. All rights reserved

Energy and Mass When a system gains or loses energy it also gains or loses a quantity of mass. E = mc2 Δm = mass defect ΔE = change in energy If ΔE is negative (exothermic), mass is lost from the system. Copyright © Cengage Learning. All rights reserved

Mass Defect (Δm) Calculating the mass defect for : Since atomic masses include the masses of the electrons, we must account for the electron mass. nucleus is “synthesized” from 2 protons and two neutrons.

Binding Energy The energy required to decompose the nucleus into its components. Iron-56 is the most stable nucleus and has a binding energy of 8.79 MeV. Copyright © Cengage Learning. All rights reserved

Binding Energy per Nucleon vs. Mass Number Copyright © Cengage Learning. All rights reserved

Nuclear Fission and Fusion Fusion – Combining two light nuclei to form a heavier, more stable nucleus. Fission – Splitting a heavy nucleus into two nuclei with smaller mass numbers. Bombardment+ Parent Daughters + neutrons Copyright © Cengage Learning. All rights reserved

Nuclear Fission To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE Copyright © Cengage Learning. All rights reserved

Criterion for a self sustaining reaction: The target nuclei must produce at least one neutrons upon splitting. The must be sufficient mass of target nuclei for the reaction to continue. The mass defect must be sufficient in order to produce high energy emissions.

Fission Processes A self-sustaining fission process is called a chain reaction. Copyright © Cengage Learning. All rights reserved

Schematic Diagram of a Nuclear Power Plant Copyright © Cengage Learning. All rights reserved

Schematic Diagram of a Reactor Core Copyright © Cengage Learning. All rights reserved

Fuel rods: Contains fissionable material What does each part do? Fuel rods: Contains fissionable material Control Rods: Conic neutron “catchers” made of boron or cadmium Heat exchanger: Web of pipes containing superheated fluid that boils the water Reactor vessel: Contains reactor core Containment fluid: Fluid that surrounds fissionable material also serves to control reaction Turbine: Spins when steam passes through

Condenser: Returns steam to water. More parts Generator: Connected to turbine. Converts mechanical Energy to electrical Condenser: Returns steam to water. External water source: Provides water for condenser. Cooling tower: Releases excess heat so water can be returned to ecosystem Pumps: Move fluid around and create elevated pressure conditions

Nuclear Waste Low Level High level

Nuclear Energy? Pros Cons

Nuclear Fusion To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE Copyright © Cengage Learning. All rights reserved

Biological Effects of Radiation Depend on: Energy of the radiation Penetrating ability of the radiation Ionizing ability of the radiation Chemical properties of the radiation source Copyright © Cengage Learning. All rights reserved

rem (roentgen equivalent for man) The energy dose of the radiation and its effectiveness in causing biologic damage must be taken into account. Number of rems = (number of rads) × RBE rads = radiation absorbed dose RBE = relative effectiveness of the radiation in causing biologic damage

Effects of Short-Term Exposures to Radiation Copyright © Cengage Learning. All rights reserved