chapter 25 nuclear chemistry. radioactivity marie and pierre curie –s–s–s–studied uranium...
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Pierre & Marie CurieTRANSCRIPT
CHAPTER 25CHAPTER 25
Nuclear Nuclear ChemistryChemistry
RadioactivityRadioactivity
•Marie and Pierre CurieMarie and Pierre Curie– Studied uranium saltsStudied uranium salts– Found that uranium emitted rays Found that uranium emitted rays
of particles even of particles even without without the the addition of outside energyaddition of outside energy
•Coined the term, Coined the term, RADIOACTIVITYRADIOACTIVITY
Pierre & Marie CuriePierre & Marie Curie
RadioactivityRadioactivityThe process by which the nucleus of The process by which the nucleus of
an atom emits particles and rays.an atom emits particles and rays.
RadiationThe rays and particles emitted by a
radioactive source.
Nuclear ReactionsNuclear Reactions• Involve the nucleus of unstable atomsInvolve the nucleus of unstable atoms
– This means This means neutronsneutrons and and protonsprotons are are involved!involved!
• Unstable atoms are called Unstable atoms are called radioisotopesradioisotopes
• The changes in the nuclei of The changes in the nuclei of radioisotopes are accompanied by large radioisotopes are accompanied by large amounts of amounts of energy.energy.
•CannotCannot be slowed down or sped up by be slowed down or sped up by outside factors!outside factors!
The stability of an The stability of an atom depends on atom depends on
it’s it’s neutron-to-proton neutron-to-proton
ratio!ratio!
Atom Builder
Nuclear reactions are different from
chemical reactions!
Chemical ReactionsChemical Reactions
• Atoms gain stability by adding, Atoms gain stability by adding, losing, or sharing losing, or sharing electronselectrons
• Affected by temperature, pressure, Affected by temperature, pressure, or the presence of catalysts.or the presence of catalysts.
CharacteristicCharacteristic Chemical Chemical ReactionReaction
Nuclear Nuclear ReactionReaction
Involves NucleiInvolves Nuclei
Involves ElectronsInvolves Electrons
Rate can be Rate can be changedchangedEmits energyEmits energy
How do nuclear reactions differ from chemical
reactions?
How did Marie & Pierre’s How did Marie & Pierre’s discovery affect Dalton’s discovery affect Dalton’s
findings?findings?• They disproved Dalton’s Theory They disproved Dalton’s Theory
by saying that atoms are NOT by saying that atoms are NOT indivisible.indivisible.
• Particles from a radioisotope are Particles from a radioisotope are separated from the nucleus separated from the nucleus during radioactive decay.during radioactive decay.
Let’s Review!Let’s Review!
The The processprocess by which unstable by which unstable atoms give off rays of particles is atoms give off rays of particles is called:called:
Radioactivity!Radioactivity!
What is the term for rays What is the term for rays and particles given off by a and particles given off by a radioactive source?radioactive source?
RadiationRadiation
What’s another word for What’s another word for an unstable isotope?an unstable isotope?
RadioisotopeRadioisotope
Name three differences Name three differences between a chemical between a chemical reaction and a nuclear reaction and a nuclear reaction:reaction:1.1.
2.2.
3.3.
Radiation is emitted Radiation is emitted during during
radioactive decayradioactive decay
There are 3 types of There are 3 types of radiation:radiation:
• Alpha RadiationAlpha Radiation• Beta RadiationBeta Radiation• Gamma RadiationGamma Radiation
Alpha RadiationAlpha Radiation• Unstable nucleus emits a Helium Unstable nucleus emits a Helium
atom atom – 2 protons and 2 neutrons2 protons and 2 neutrons
• The mass number of the The mass number of the original atom decreases by 4original atom decreases by 4
• The atomic number of the original The atomic number of the original atom decreases by 2atom decreases by 2
An example of An example of alpha alpha radiationradiation::• The symbol for helium is:The symbol for helium is:
He He (2 protons & 2 (2 protons & 2 neutrons)neutrons)
U Th + HeU Th + He
alpha radioactivity corresponds to the emission of a helium nucleus, a particularly stable structure consisting of two protons and two neutrons, called an a particle.
The Band The Band of Stability of Stability
Facts about alpha Facts about alpha particles:particles:• They are the nuclei of helium atomsThey are the nuclei of helium atoms• They have two protons, so they have They have two protons, so they have
a a postitive chargepostitive charge• They can be sheilded by paper and They can be sheilded by paper and
clothingclothing• They are They are harmfulharmful if ingested if ingested
Beta RadiationBeta Radiation• The weak nuclear force is overcome and The weak nuclear force is overcome and
nuclear particles begin to break.nuclear particles begin to break.• If a neutron breaks apart = electron and a If a neutron breaks apart = electron and a
proton.proton.• These are the symbols you need to know:These are the symbols you need to know:Electron= Electron= ee Proton = Proton = HH
NeutronNeutron = = nn
Beta Radiation Beta Radiation Continued:Continued:• When the neutron breaks, the proton When the neutron breaks, the proton
stays in the nucleusstays in the nucleus• The electron, which is fast moving, is The electron, which is fast moving, is
released from the atomreleased from the atom• Here’s what happens:Here’s what happens:
n H + en H + e
When there are too many neutrons, the atom becomes stable by splitting a neutron.
How does this change the atomic number of the original atom?
A little more on Beta A little more on Beta radiation:radiation:• Look what happens to carbon-14:Look what happens to carbon-14:
C N + eC N + e• When a neutron in carbon splits, a proton is When a neutron in carbon splits, a proton is
gained, changing carbon’s atomic # to 7—which gained, changing carbon’s atomic # to 7—which means it’s not Carbon, anymore! It’s changed to means it’s not Carbon, anymore! It’s changed to Nitrogen. Nitrogen.
• The left-over electron is released from the atom!The left-over electron is released from the atom!• This happens when there are too manyThis happens when there are too many
neutronsneutrons!!
Positrons Positrons (still a part of Beta (still a part of Beta
radiation)radiation)• A positron occurs when a proton is A positron occurs when a proton is
converted into a neutron.converted into a neutron.• This occurs when the nucleus of a This occurs when the nucleus of a
radioisotope has radioisotope has too manytoo many protons protons for the number of neutronsfor the number of neutrons!!
Cl S + Cl S + e01
So when there are too many protons, a proton splits and a positron is
emitted.
What does losing a proton do to the atomic # of the original atom?
Facts about Beta Facts about Beta particles:particles:• They have They have less chargeless charge than alpha than alpha
particles.particles.• They have They have less massless mass, so they’re more , so they’re more
penetrating. penetrating. – They can pass through paper but can be They can pass through paper but can be
stopped by aluminum foil or wood.stopped by aluminum foil or wood.• They can be electrons (They can be electrons (ββ-) or -) or positrons positrons
((ββ+)+)
A proton changed into a neutron, beta+ radioactivity, characterized by the emission of positron.
The Band The Band of Stability of Stability
Transformation of a neutron into a proton, beta- radioactivity, characterized by the emission of an electron.
The Band The Band of Stability of Stability
Gamma RadiationGamma Radiation• Gamma rays are high-energy photonsGamma rays are high-energy photons• They are electromagneticThey are electromagnetic• Have no mass Have no mass • Have no chargeHave no charge• Are extremely penetrating & harmfulAre extremely penetrating & harmful• Can be stopped by several meters of Can be stopped by several meters of
concrete or centimeters of leadconcrete or centimeters of lead
Gamma Rays cont’d.Gamma Rays cont’d.• Nuclei often emit alpha or beta Nuclei often emit alpha or beta
particles along with gamma rays:particles along with gamma rays:
Th Ra + He + Th Ra + He + γγ
gamma radioactivity is not related to a transmutation of the nucleus. It results in the emission, by the nucleus, of an electromagnetic radiation, like visible light or X-rays, but more energetic.
gamma radioactivity can occur by itself or together with alpha or beta radioactivity.