Nuclear Chemistry – Day 3Nuclear Chemistry – Day 3

Welcome! Please pick up the practice Welcome! Please pick up the practice questions on half-lives. We will complete questions on half-lives. We will complete this prior to the quiz.this prior to the quiz.

Turn in your honors intent letter today.Turn in your honors intent letter today.

Hmwk: Read Chapter 9 Section 2 and 3Hmwk: Read Chapter 9 Section 2 and 3

Test next Monday/TuesdayTest next Monday/Tuesday

Notebook check next timeNotebook check next time

Honors Proposal due next week.Honors Proposal due next week.

Warm-UpWarm-Up

Complete the half-lives and radioactive Complete the half-lives and radioactive decay practice questions.decay practice questions.

AgendaAgenda

AnnouncementsAnnouncementsWarm-Up: Practice QuestionsWarm-Up: Practice QuestionsQuiz – Half-lives & Radioactive DecayQuiz – Half-lives & Radioactive DecayNotes: Fission/Fusion Notes: Fission/Fusion Video: Nuclear EnergyVideo: Nuclear Energy

Nuclear ForcesNuclear Forces

Protons and neutrons are tightly packed in the Protons and neutrons are tightly packed in the nucleusnucleus

Unstable nuclei undergo decay by emitting Unstable nuclei undergo decay by emitting nuclear radiationnuclear radiation

An element can have both stable and unstable An element can have both stable and unstable isotopesisotopes

The stability of a nucleus depends on the The stability of a nucleus depends on the nuclear forces that hold the nucleus together: nuclear forces that hold the nucleus together: these forces act between the protons and the these forces act between the protons and the neutrons.neutrons.

Why don’t the positively charged Why don’t the positively charged protons repel each other ?protons repel each other ?

Strong nuclear forceStrong nuclear force: causes protons : causes protons and neutrons to attract each other.and neutrons to attract each other.

This attraction is much stronger than the This attraction is much stronger than the electric repulsion between protonselectric repulsion between protons

Too many neutrons or protons can Too many neutrons or protons can cause a nucleus to become cause a nucleus to become

unstable and decayunstable and decay

Nuclei with more than 83 protons are Nuclei with more than 83 protons are always unstablealways unstable

These nuclei will always decay – releasing These nuclei will always decay – releasing large amounts of energy and nuclear large amounts of energy and nuclear radiation.radiation.

The decay results in a more stable The decay results in a more stable nucleus.nucleus.

Nuclear FissionNuclear Fission

Fission: The process of splitting heavier Fission: The process of splitting heavier nuclei into lighter nuclei; the process by nuclei into lighter nuclei; the process by which a nucleus splits into two or more which a nucleus splits into two or more fragments and releases neutrons and fragments and releases neutrons and energyenergy

Nuclear Fission – Video Clip

Nuclear Weapons: In fission weapons, a mass of (enriched uranium or plutonium) is assembled into a supercritical mass—the amount of material needed to start an exponentially growing nuclear chain reaction—either by shooting one piece of subcritical material into another, or by compressing a subcritical mass with chemical explosives, at which point neutrons are injected and the reaction begins.

Nuclear Power Plants: Nuclear energy is produced when a fissile material, such as uranium-235 (235U), is concentrated such that nuclear fission takes place in a controlled chain reaction and creates heat — which is used to boil water, produce steam, and drive a steam turbine. The turbine can be used for mechanical work and also to generate electricity.

Nuclear FusionNuclear Fusion

Fusion: the process in which light nuclei Fusion: the process in which light nuclei combine at extremely high temperatures, combine at extremely high temperatures, forming heavier nuclei and releasing forming heavier nuclei and releasing energyenergy

How the Sun shines Nuclear fusion is the energy source of stars – just like our own Sun.

It has a nuclear fusion reactor at its core.

The immense pressure and a temperature of 16 million degrees C force atomic nuclei to fuse and liberate energy.

About four million tons of matter is converted into sunlight every second.

Nuclear Radiation TodayNuclear Radiation Today

Nuclear radiation is all around you. Nuclear radiation is all around you. Background radiationBackground radiation is the nuclear is the nuclear radiation that arises naturally from cosmic radiation that arises naturally from cosmic rays and from radioactive isotopes in the rays and from radioactive isotopes in the soil and air.soil and air.

Radiation is measured in units of rems.Radiation is measured in units of rems.Exposure varies depending on location Exposure varies depending on location

and activities.and activities.

Beneficial Uses of Nuclear Beneficial Uses of Nuclear RadiationRadiation

Smoke detectors – a small alpha-emitting Smoke detectors – a small alpha-emitting isotope is used to detect smoke particles isotope is used to detect smoke particles in the air.in the air.

Disease detection – radioactive tracers are Disease detection – radioactive tracers are added to a substance so that its added to a substance so that its distribution can be detected later. These distribution can be detected later. These are widely used in medicine.are widely used in medicine.

D:\Ch09\75459.htmlD:\Ch09\75459.html tracer clip tracer clip

Benefits continuedBenefits continued

Nuclear radiation therapy is used to treat Nuclear radiation therapy is used to treat cancer.cancer.

Agriculture - radioactive tracers and radio-Agriculture - radioactive tracers and radio-isotopes are used to help scientists isotopes are used to help scientists understand biological processes in plants.understand biological processes in plants.

MRI image of a healthy brainMRI image of a healthy brain

MRI image of a brain with MRI image of a brain with Alzheimer’s DiseaseAlzheimer’s Disease

Possible Risks of Nuclear RadiationPossible Risks of Nuclear Radiation

Nuclear radiation can ionize atomsNuclear radiation can ionize atoms Ionization is a change in the number of Ionization is a change in the number of

electrons in an atom or molecule, causing the electrons in an atom or molecule, causing the particle to be positively or negatively charged.particle to be positively or negatively charged.

Radiation sickness results from high levels Radiation sickness results from high levels of nuclear radiationof nuclear radiationStudies have shown a relationship between Studies have shown a relationship between

high levels of radiation exposure and cancer.high levels of radiation exposure and cancer.

(Risk is determined by amount of exposure)(Risk is determined by amount of exposure)

Nuclear PowerNuclear Power

Nuclear fission is an alternative to fossil Nuclear fission is an alternative to fossil fuels as a source of energy.fuels as a source of energy.

Radioactive products of fission must be Radioactive products of fission must be handled carefully and nuclear waste must handled carefully and nuclear waste must be safely stored.be safely stored.

Scientists are working on nuclear fusion Scientists are working on nuclear fusion reactors, but fusion reactions are difficult reactors, but fusion reactions are difficult to produce in the laboratory.to produce in the laboratory.