Presentation on theme: "Unit 1.3 Nuclear Chemistry"— Presentation transcript:
1Unit 1.3 Nuclear Chemistry 1.3-1 Types of Radioactivity
2Learning Objectives By the end of this section you will be able to: Observe nuclear changes and explain how they change an element.Express alpha and beta decay in nuclear equations.Model the half life of an isotope.Explain how half life is used to date materials.
4Discovery of Radioactivity Radioactivity is the spontaneous emission of radiation by an unstable atomic nucleus.
5Chemical Reactions vs. Nuclear Reactions Occur when bonds are broken and formedOccur when nuclei combine, split and emit radiationInvolve only valence electronsCan involve protons, neutrons and electronsAtoms keep the same identity although they gain, lose or share electronsAtoms of one element are often converted into atoms of another elementAssociated with small changes in energyAssociated with large changes in energyTemperature, pressure, concentration and catalysts affect reaction ratesTemperature, pressure, concentration and catalysts do not affect reaction rates
6Nuclear ReactionsNuclear reactions involve the protons and neutrons found in the nucleusDuring nuclear reactions a nucleus can gain or lose protons and neutrons.
7Nuclear ReactionsRemember that the number of protons determines the identity of an element.Changing the number of protons changed the element into another element.During nuclear reactions atoms of one element are changed into atoms of another element
8Nuclear NotationDifferent isotopes of atoms can be represented using nuclear notation.
9Review of Nuclear Notation In your notebook write the following isotopes in nuclear notation.Hydrogen-1Hydrogen-2Hydrogen-3
10Radiation causes Radioactive Decay Radioactive decay is the release of radiation by radioactive isotopes.Not all radioactive isotopes decay in the same way.Different types of decay change the nucleus in different ways.The three types of decay are:AlphaBetaGamma decay
11Radioactive ALPHA Decay Alpha decay is the release of alpha particles (2 protons and 2 neutrons).Alpha particles are helium nuclei consisting of two protons and two neutrons.Alpha particles are represented as or α.
12Radioactive ALPHA Decay Alpha particles, which are large in size, collide with objects around them.Do not penetrate very deeplyAre easily stopped by a thin layer of material.
13Radioactive ALPHA Decay Alpha decay causes the decaying nucleus to lose 2 protons and 2 neutrons.This means:the mass # decreases by 4 (2P and 2N)The atomic # decreases by 2ExamplesParent Daughter alpha particle
14Equation for Radioactive ALPHA Decay The parent element turns into a daughter element with a mass number 4 less and an atomic number 2 less than the parent!Does this reaction demonstrate the law of conservation of matter?How can we check it? Explain
15ALPHA Emission + Energy! Two protons and neutrons are lost The protons and neutrons leave as an alpha particle.+ Energy!
16Radioactive Alpha Decay Write the equation for alpha decay for the following particle in your notebook.Thorium-230
17Radioactive BETA Decay Beta decay is the release of beta particles from a decaying nucleus.A beta particle is a high energy electron with a 1- charge.Beta particles are written as β- orBeta particles pass more easily through matter than alpha particles and require sheets of metal, blocks of wood or specialized clothing to be stopped.
18Radioactive BETA Decay The electron released during beta decay is not one of the original electrons that existed outside the nucleus.The beta particle (electron) is produced by the change of a neutron into a proton and an electron.Mass# is same!Parent Daughter Beta(add P+) (sub e-)
19Equation for Radioactive BETA Decay The parent nucleus turns into a daughter with an atomic number 1 greater.The mass number stays the same.
20BETA EmissionA neutron becomes a proton (which stays in the nucleus) and electron (which is ejected from the atom).ADD A PROTON and LOSE an ELECTRON+ ENERGY
21Radioactive BETA Decay Write the equations for beta decay for the following particles.Magnesuim-27Sulfur-35
22Radioactive Gamma Decay Gamma decay is the release of gamma rays from a nucleus.A gamma ray is a high energy form of electromagnetic radiation with out a change in mass or charge.
23Radioactive GAMMA Decay Gamma rays have high penetrating ability and are very dangerous to living cells.To stop gamma rays thick blocks of lead or concrete are needed.
24Radioactive GAMMA Decay During gamma decay only energy is released!Gamma decay does not generally occur alone, it occurs with other modes of decay. (alpha or beta)
25Equation for Radioactive GAMMA Decay with Beta or Alpha Decay When gamma decay is expressed in an equation it is expressed as γ.Electron from beta decay is captured to cause gamma particle to emit.The following equation shows both gamma and alpha decay occurring.
27Construct a similarities and differences chart comparing the 3 types of decay! (10 min) Decay TypeGives offChanges Nuclear notation by:Radiation penetration and harm to cellsAlphaBetaGamma
28Similarities and Differences Decay TypeGives offChanges Nuclear notation by:Radiation penetration and harm to cellsAlpha2 protons & 2 neutrons= Alpha particle=42 HeMass number decreases by 4Atomic number decreases by 2Large particle, easily stopped by clothVery low riskBetaBeta particle= electron =0-1eAtomic number increases by 1The mass number stays the sameThese high energy particles pass more easily through matterNeed metal sheets to stopModerate risk to cellsGammaA gamma ray a high energy form of electro-magnetic radiationNo change in mass or atomic numberBUT does not occur aloneAccompanied by alpha or beta.Gamma rays have high penetrating abilityTo stop gamma rays thick blocks of lead or concrete are needed.Very dangerous to living cells.
29Quiz!! PLEASE DO NOT WRITE THE QUESTIONS! Each correctly answered question is worth 1 point!What are the three types of decay?Explain what occurs to the element in each type of decay, be specific.A.B.C.Which type of decay is least harmful to living cells.Which is most harmful?If Uranium-238 alpha decays, what would the decay equation be?
30Answers to quiz questions Alpha, beta and gammaAlpha- gives off alpha particle which is 2 protons and 2 neutrons. It reduces the atomic number by 2 and the mass by 4 so becomes a new elementBeta- a neutron becomes a proton and an electron and gives off the electron, it adds 1 to the atomic number but leaves the mass number the same so a new element is formedGamma- just a gamma ray, pure electromagnetic radiation (energy)3. Alpha4.Gamma5 238 U -> 234 Th + 4 He
31Nuclear Equations: What type of decay is Represented Nuclear Equations: What type of decay is Represented? Fill in the blanks
33Radioactive DecayRadiation can be detected with Geiger counters and scintillation counters.Geiger counters detect ionizing radiation.Scintillation counters register the intensity of radiation by detecting light.
34Rate of Radioactive Decay It is impossible to predict when a specific nucleus in a sample of radioactive material will undergo decay.The rate of overall decay is constant so that it is possible to predict when a given fraction of a sample will have decayed.
35Half-LifeHalf-life is a term used to describe the time it takes for half of a given amount of a radioactive isotope to decay.Half-life varies greatly depending on the isotope
38Half-Life and Radioisotope Dating Radioactive decay has provided scientists with a technique for determining the age of fossils, geological formations and human artifacts.Four isotopes are commonly used for dating objectsCarbon-14Uranium-238Rubidium-87Potassium-40
39Half-Life and Radioisotope Dating;C-14 Carbon-14 DatingAll organisms take in carbon during their lifetime.When organisms die they stop taking in carbon.Most carbon that organisms take in is stable (Carbon-12 or Carbon-13).About one atom in a million is Carbon-14.While the organism is alive the amount of Carbon-14 in its tissues remains constant.After the organism dies no more Carbon-14 is taken in and the amount begins to decline at a predictable pace. (half-life of C-14=5730 years)
41Half-Life and Radioisotope Dating The half-life of Carbon-14 is years.Objects greater than 60,000 years old cannot be dated using this method because the amount of Carbon-14 that remains is too small to be detected.Objects greater than 60,000 years old are dated using:Uranium-238 (t½ = 4.5 billion years)Rubidium-87 (t½ = 48 billion years)Potassium-40 (t½ = 1.25 billion years)