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CHEMISTRY 1 Nuclear Chemistry. Chapter 28. NUCLEAR CHEMISTRY. 1896- Antoine Becquerel discovered ___________________ He accidently left uranium ore on top of photographic plates. They became fogged from the exposure. Becquerel had 2 graduate students: _______________ _______________. - PowerPoint PPT Presentation


Agenda 1/14/2013 and 1/15/2013

CHEMISTRY 1Nuclear ChemistryChapter 28

NUCLEAR CHEMISTRY1896- Antoine Becquerel discovered ___________________He accidently left uranium ore on top of photographic plates. They became fogged from the exposure. Becquerel had 2 graduate students: _______________ _______________

radioactivityMarie &Pierre Curie_______________________- the property by which uranium gives off rays______________________-penetrating rays emitted by a radioactive source.

In 1903, the Curies and Becquerel won Nobel prizes for this discovery.RadioactivityRadiationTypes of Radiation1. Alpha emission -helium nuclei emitted from a radioactive source2 protons & 2 neutrons2+ chargeSymbol is Dont travel far and are not very penetratingStopped by a sheet of paperCant penetrate skin, but dangerous if ingestedVery common with heavy nuclides

HeWrite thisAlpha Decay ()Lose 2 protons (+2 charge) & 2 neutrons

He42Examples:U ___ + He

Ra Rn + He

2228623892ThLaw of conservation of massAtomic #Mass # = # protons + # neutrons226 8842222 86RaRn + HeAtomic #8886 + 2Mass #226222 + 4

2. Beta emission - fast moving ___________ formed by the decomposition of a neutron of an atom. The neutron breaks into a proton and an electron. The proton stays in the nucleus and the electron is ejected. (net effect: neutron changes into proton)Write this:n H + e

electronsMuch smaller than alpha particlesSymbol is Charge is -1Much more penetrating than alpha particlesStopped by aluminum foil or thin pieces of wood

C N + e

eWrite this

Beta Decay ()Lose electron (-1 charge, no mass) 0-1CN + 14 614 7 0-1

3. Gamma emission - _________________ _____________ (high energy) emitted from a nucleus as it changes from an excited state to a ground energy state.Often emitted along with or radiationSymbol is Has no mass & no chargeHigh energy photon U He + Th + 2

electromagneticradiationthe emission of gamma rays is one way that a nucleus with excess energy (in an excited nuclear state) can relax to its ground stateExtremely penetrating, very dangerousStopped somewhat by several feet of concrete or several inches of lead

Gamma Emission ()00No mass, no charge, loses just energy4. Positron emission- ___________________________________ eAntimatterNet effect: changes proton to a neutronOccurs when neutron/proton ratio is too small

Na e + Ne

Particle with the mass of an electron but a positive chargeWrite this (the 0 and the +1)

Alpha radiation cannot penetrate the skin and can be blocked out by a sheet of paper, but is dangerous in the lung.

Beta radiation can penetrate into the body but can be blocked out by a sheet of aluminum foil.

Gamma radiation can go right through the body and requires several centimeters of lead or concrete, or a meter or so of water, to block it. Nuclear Transformation (Transmutation)- ____________________________________bombarding with alpha particles

Bombarding with neutrons

N + He O + H

U + n U

Changing one element into anotherWrite theseFill in the blanks (not in your notes): Co Ni + ____

Am Np + ____

Th He + ____

N + ____ C + H60276026 0 1241 95237 93421114 614 7230 9042226 88Ra10nHee

Half-life (t1/2)the time required for of the atoms of a radioisotope to emit radiation and decay to productsthe longer the half-life, the more _____________ the isotopevaries from fractions of a second to millions of yearsstableExamplesNitrogen-13 decays to carbon-13 with a half-life of 10 minutes. How long is 4 half lives? 4 half livesX10 min/half life=40 min.If you start with 2.00 g of nitrogen-13 how many grams will remain after 4 half lives?2.00 g1.00 g0.500 g0.250 g0.125 g4321Phosphorous-32 has a half-life of 14.3 yr. How many grams remain after 57.2 yr from a 4.0 g sample? 57.2 yr14.3yr / half-life=4 half-lives4.0 g2.0 g1.0 g0.50 g3210.25 g4Carbon-14 datingCarbon-14 is continuously produced in the ____________ when high energy neutrons from outer space collide with nitrogen-14 in the air.N + n C + H

atmosphereCarbon-14 combines with oxygen to form CO2 which is incorporated into plant materials. As long as the plant or animal is alive, decaying carbon-14 is continuously replaced. After death, the carbon-14 decays at a steady rate. Carbon-14 decays to Nitrogen-14C e + N

The proportion of carbon-14 in the atmosphere is relatively constant. The carbon-14/carbon-12 ratio is used to identify the age of wood, cloth and other ______________ artifacts. The half-life of carbon-14 is _______________ years.

Only works for organic materialsAdjusted for change in % C-14 over the yearsorganic5730ExampleIf the C-14 in a fossil sample is only 1/4 what it is in living organisms, how old is the object?To have remaining, 2 half lives have passed.2X5730 yr=11,460 yr.Fission - splitting a heavy nucleus into two nuclei with smaller mass numbers.used for _____________________

production of ______________causes a chain reaction (which must be controlled)1 kg of uranium-235 is equivalent to 20,000 tons of dynamitenuclear energy n + U Ba + Kr + 3 n


Fission splitting of atoms.FISSION: splitting of atomsFission in a nuclear reactor is carefully controlled. Much of the energy is _______. This energy is used to produce _________ and subsequently, __________________. A _________________(usually water) is needed.The water (or carbon) also acts as a moderator. It _____________the neutrons down so that they can be captured by the U-235 fuel. Control rods made of _______________ are present to absorb excess neutrons to slow down the reaction. They can be raised or lowered into the reactor core. heatsteamelectricitycoolantslowscadmiumFusion- combining two light nuclei to form a heavier, more stable nucleusstars produce their energy this wayCurrently __________________ are necessary in order to initiate fusionpossible future energy sourcehigh temperatures4 H + 2e He + energy

Fusion two nuclei combine to form a heavier nucleus.

FUSION: two nuclei combine to form a heavier nuclei

Proton-proton chain reactionFusion reaction in our Suns core.Proton-proton chain reaction