chapter 4 & 25 nuclear chemistry

Download Chapter 4 & 25 Nuclear Chemistry

Post on 23-Feb-2016




0 download

Embed Size (px)


Chapter 4 & 25 Nuclear Chemistry. Chapter 4 & 25 Nuclear Chemistry. 4.4 Unstable Nuclei and Radioactive Decay. Chemical reactions involve only electrons, NOT the nucleus. Protons determine the identity of an atom. Change the protons, it is a different atom!!. - PowerPoint PPT Presentation


Chapter 4 & 25 Nuclear Chemistry

Chapter 4 & 25 Nuclear ChemistryChapter 4 &25 Nuclear Chemistry

4.4 Unstable Nuclei and Radioactive DecayChemical reactions involve only electrons, NOT the nucleus.Protons determine the identity of an atom. Change the protons, it is a different atom!! 4.4 Unstable Nuclei and Radioactive DecayNuclear Reactions- reactions which involve a change in an atoms nucleus

3Radioactivity- substances spontaneously emit radiation

Radiation- rays and particles emitted by the radioactive materialBy emitting radiation, atoms of one element can change into atoms of another element.

5Radioactive atomsEmit radiation because their nuclei are unstable. Radioactive decay- a spontaneous process in which unstable nuclei lose energy by emitting radiation

Unstable radioactive atoms undergo radioactive decay until they form stable non radioactive atoms of a different element.

History of Radioactivity Chapter 25: Nuclear Chemistry25.1 Nuclear Radiation1895- William Roentgen; discovered x-rays (form of high-energy electromagnetic radiation)rays caused photographic plates to darken

9He took pictures of his wifes hand.rays caused photographic plates to darkenIn 1901 Rntgen was awarded the very first Nobel Prize in Physics.

Henri Becquerel1896 - studied minerals that emit light after being exposed to sunlight- called phosphorescence.He wondered if they also emitted X-rays.

11Accidentally, he discovered uranium emitted radiation without an external source of energy such as the sun. Becquerel had discovered radioactivity, the spontaneous emission of radiation by a material.

Later, Becquerel demonstrated that the radiation shared certain characteristics with X rays but, unlike X rays, radiation could be deflected by a magnetic field and therefore must consist of charged particles. For his discovery of radioactivity, Becquerel was awarded the 1903 Nobel Prize for physics.

The CuriesMarie Curie and Pierre Curie took Becquerels mineral and isolated components; found that rays were being emitted by Uranium they called this process radioactivityMarie discovered that the uranium nucleus is radioactiveBecquerel & Curies shared Nobel prize for their work1898 - Marie and Pierre Curie isolated the elements that were emitting the rays. polonium, and radium

Rate of radioactive emission of charged particles from elements could be measured and compared. In addition, she found that there was a decrease in the rate of radioactive emissions over time and that this decrease could be calculated and predicted. But perhaps Marie Curie's greatest and most unique achievement was her realization that radiation is an atomic property of matter.Nobel Prize in Physics 1903 was shared; Curies and Becquerel for work in radioactivityNobel Prize in Chemistry 1911 Marie Curie for her work with the elements Polonium and Radium.3 Types of Radiation1800s Scientists directed radiation between 2 electrically charged plates and found there were 3 different types; some deflected to the negative, some to the positive, and some were not deflected at all. Types of RadiationRadioisotopes- isotopes of atoms with unstable nucleiC-14 is a radioisotope of C-12Most common types of radiation are alpha, beta, and gamma rays


Alpha Particlean alpha particle (we use the symbol ) is positiveAlpha Radiation- radiation deflected toward the negatively charged plate

Alpha particlecontains 2 protons 2 neutrons and has a 2+ chargeHas a mass number of 4

Alpha Radiation

24Positive charge is why it is attracted to negative plateEquivalent to helium-4 nucleus Ex:

Beta Radiationa beta particle (symbol ) is negativeBeta Radiation- radiation that was deflected towards the positively charged plateBeta Particles- radiation consisting of fast moving electronsBeta particles consist of an electron with a 1- chargeEx:

Beta Particles A neutron becomes a proton and an electron. The electron leaves the atom at high speed.

What blocks these rays!

Gamma Radiationa gamma ray (symbol ) is neutralGamma Rays- high-energy radiation that possesses no mass and no chargeUsually accompany alpha and beta radiation

Accounts for most of the energy lost during radioactive decayGamma rays cannot result in the formation of a new atomEx:

What blocks these rays!

Practice worksheet 25.4 Fission and Fusion of Atomic NucleiNuclear Fission- the splitting of a nucleus into fragments; accompanied by a very large release of energy

34During fission, a neutron collides into an unstable nucleus causing a chain reaction

The neutrons released can cause more fissions, which releases more neutrons causing more fissions and so on.

Chain reaction self-sustaining process in which one reaction initiates the next.

Critical mass a sample that is massive enough to sustain a chain reaction.

More than a critical mass can generate a nuclear explosion.Nuclear Fission ReactionHeavier isotopes is broken down into lighter isotopes

Uses of FissionNuclear Power plantsBuilding of the A-bombFusionNuclear Fusion- the combining of atomic nuclei; capable of releasing large amounts of energyEx.: Sun powered by a series of fusion reactionshigh amount of energy is required to create reactionFusion Equation

25.5 Applications and Effects of Nuclear ReactionsIonizing radiation - radiation energetic enough to ionize (damage) matter with which it collides.Detected by Geiger counters42

Uses of RadiationRadiotracer - radioisotope that emits non-ionizing radiation and is used to signal the presence of an element or specific substance.a. analyze reactionsb. detect diseasesc. PET scansPET scan (positron emission tomography)

Medical Uses of RadiationDiagnostic: Radiotracers such as technitium-99 can be injected in the blood stream and then tracked through the body to see if organs are functioning properly; also can help diagnose cancer (PET scan)46Therapy: Radiation treatments can kill the cancer cells in cancer patients

47Commercial applicationsSmoke detectors: have a tiny mass of americium-241, which is a source of alpha radiation

Rifle sights: tritium is used with phosphor to increase nighttime firing accuracy

48Exit signs: luminescence is due to a small amount of radioactivity

Food irradiation: exposing food to ionizing radiation to destroy microorganisms, bacteria, viruses, and insects

X-RaysX-rays and gamma rays high-energy electromagnetic radiation that is extremely penetrating and damaging to living tissue. Blocked by lead and concrete.

Radiochemical DatingThe half-life of any radioisotope is constantRadiochemical dating process of determining the age of an object by measuring the amount of a certain radioisotope remaining in that object.ConcernsRadioactive materials have long half-lives and continue to be damaging for many yearsNo good way to dispose of nuclear waste because it can contaminate water, soil, and air52