chapter 25 nuclear chemistry. radioactivity marie and pierre curie –s–s–s–studied uranium...

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.