Nuclear Nuclear ChemistryChemistry

Ch 4.5 & 25Ch 4.5 & 25

Nuclear Reactions vs. Normal Chemical

Changes• Nuclear reactions- reactions that

take place inside the nucleus of an atomatomCHEMICAL REACTIONS NUCLEAR REACTIONS

Bonds are broken and formed Nuclei emit particles and/or rays

Atoms remain unchanged, only rearranged2H2 + O2 2H2O

Atoms are changed into other atoms of different elements

Involve valence electrons Involves the nucleus, P+, N0, e-

Small energy changes large energy changes (BINDING Energy)

Rate influenced by conc, temp., pressure and catalyst

Not affected by those

HeThU 42

23490

23892

RadioactivityRadioactivity• One of the pieces of evidence for the fact

that atoms are made of smaller particles came from the work of Marie Marie Curie Curie a Polish scientist (1876-1934).

• She discovered radioactivity, radioactivity, the spontaneous disintegration of some elements into smaller pieces (other elements).

RadioactivityRadioactivity• Many nuclei are radioactive.

• This means they are unstable and will decay by emitting a particle or ray, transforming the nucleus into another nucleus, or into a lower energy state.

• A chain of decays takes place until a stable nucleus is reached.

Radioactivity &Radioactivity & Unstable Unstable AtomsAtoms• If # of neutrons is too high or too low, the nucleus

becomes unstable and emits energy.• Any atom containing an unstable nucleus is called

a radioactive isotope or radioisotope

***More than 1,500 different **More than 1,500 different nuclei are known. Of those, nuclei are known. Of those, only 264 are stable and do only 264 are stable and do not decay or change withnot decay or change with time. These nuclei are in atime. These nuclei are in a region called the band of region called the band of stability.stability.

IsotopesIsotopes• have the same number of p____,

different number of n_____• Another way to show an

isotope is to have the mass number follow the name of the element (Carbon-14 or C-14)

IsotopesIsotopes39

19 K ; 4019 K 14

6C ; 126 C

• Superscript is the mass number

• Subscript is the atomic number

Types of Nuclear RadiationTypes of Nuclear Radiation

1. Alpha 2.Beta 3. Gamma

Alpha DecayAlpha Decay

• Alpha particle—a positively charged particle (helium isotope(helium isotope) )

made up of two p+ & two no

• the least penetrating • can be stopped by a sheet of

paper• Symbols: , He4

2

Alpha DecayAlpha Decay• An alpha particle looks like a helium

atom (42He)

• massmass reduces by 4 ,the atomic atomic # reduces by 2

• Examples:238238

9292 U 234 2349090Th + 4

2He 209209

8484 Po 2052058282Pb + 4

2He

Parent cell

Daughter cell

Beta DecayBeta Decay

• A A beta particlebeta particle is an e- is an e- emitted by an unstable emitted by an unstable nucleusnucleus

• can be stopped by a thin can be stopped by a thin sheet of metal such as sheet of metal such as aluminumaluminum

• Symbols: Symbols: , , e01

Beta DecayBeta Decay • A beta particle is written 0

-1e ()• mass remains the same & the atomic #

increases by one• Examples:214

82Pb2142148383Bi + 0

-1e

21884Po218218

8585At + 0-1e

Gamma decayGamma decay• A gamma ray is a penetrating

ray of energy (photon) emitted by an unstable nucleus

• Gamma rays are energy waves that travel through space at the speed of light

• Symbols: , 00

Gamma Gamma decay (decay ())

• atomic # and mass remain the same, but the energy of nucleus decreases

• Gamma rays are often emitted along with alpha &/or beta particles

• Gamma rays can be stopped by several centimeters of lead or by several meters of concrete

Penetrating AbilityPenetrating Ability

Other Nuclear ParticlesOther Nuclear Particles

e01

n10• Neutron

• Positron – a positive electron

•Proton – usually referred to as hydrogen-1

•Any other elemental isotope

H11

Balancing Nuclear ReactionsBalancing Nuclear Reactions•In the reactants (starting materials – on the left side of an equation) and products (final products – on the right side of an equation)

Atomic numbers must balanceand

Mass numbers must balance

•Use a particle or isotope to fill in the missing protons and neutrons

Nuclear Reactions

Reactions that occurnaturally as nuclei strive to be stable.

Learning Check

What radioactive isotope is produced in the following bombardment of boron?

10 B + 4 He ? + 1 n 5 2 0

Learning Check

What radioactive isotope is produced in the following bombardment of boron?

10B + 4He 13 N + 1 n 5 2 7 0

Write Nuclear Equations!

Write the nuclear equation for the beta emitter Co-60.

60 Co 60 Ni + 0 e 27 28 -1

Half-LifeHalf-Life•HALF-LIFEHALF-LIFE is the time that it takes for 1/2 a is the time that it takes for 1/2 a

sample to decompose.sample to decompose.• The rate of a nuclear transformation depends only The rate of a nuclear transformation depends only

on the “reactant” concentration.on the “reactant” concentration. Amount remaining = Initial amount x (1/2)t/T

• t/T, where t is the elapsed time and T is the duration of the half-life.

Half-LifeHalf-Life

Decay of 20.0 mg of Decay of 20.0 mg of 1515O. What remains after 3 half-lives? O. What remains after 3 half-lives? After 5 half-lives?After 5 half-lives? 2.5mg0.625mg

Kinetics of Radioactive Kinetics of Radioactive DecayDecay

For each duration (half-life), one half of the substance decomposes.

For example: Ra-234 has a half-life of 3.6 daysIf you start with 50 grams of Ra-234

After 3.6 days > 25 gramsAfter 3.6 days > 25 grams

After 7.2 days > 12.5 gramsAfter 7.2 days > 12.5 grams

After 10.8 days > 6.25 gramsAfter 10.8 days > 6.25 grams

Learning Check!

The half life of I-123 is 13 hr. How much of a 64 mg sample of I-123 is left after 39 hours?

Detecting Detecting RadiationRadiation

• Devices used to detect radiation include Geiger counters & film badges

Radiocarbon DatingRadiocarbon DatingRadioactive C-14 is formed in the upper atmosphere Radioactive C-14 is formed in the upper atmosphere

by nuclear reactions initiated by neutrons in by nuclear reactions initiated by neutrons in cosmic radiationcosmic radiation

1414N + N + 11oon ---> n ---> 1414C + C + 11HH

The C-14 is oxidized to COThe C-14 is oxidized to CO22, which circulates , which circulates through the biosphere.through the biosphere.

When a plant dies, the C-14 is not replenished.When a plant dies, the C-14 is not replenished.But the C-14 continues to decay with tBut the C-14 continues to decay with t1/21/2 = 5730 = 5730

years.years.Activity of a sample can be used to date the sample.Activity of a sample can be used to date the sample.

Limits to Carbon Dating

• Some organic material must be present and must be from an organism that once lived.

• Cannot reliably detect objects more than 75,000 years old.

Radiation in Real Radiation in Real lifelife

Radiation Everyday

Fission is the splitting of a nucleus into Fission is the splitting of a nucleus into smaller fragments. Done by Neutron smaller fragments. Done by Neutron

BombardmentBombardment

Nuclear FissionNuclear Fission

A uranium-235 nucleus is struck by a neutron with ordinary thermal energy. An unstable uranium-236 nucleus is formed, but it breaks into two fragments with the release of several neutrons. The neutrons can induce the fission of other uranium-235 nuclei.

FISSION

Uranium-235 and Plutonium-239 are the only fissionable isotopes.

FISSION• Since the one original neutron causing the reaction has

resulted in the production of three neutrons, there is the possibility of a chain reaction occurring.

A chain reaction

Atomic Bombs• This is what happens in an atomic bomb.• A fission bomb uses an uncontrolled

nuclear fission chain reaction to release an enormous amount of energy in a small amount of time.

Nuclear Fission & Nuclear Fission & POWERPOWER

• Currently about 103 Currently about 103 nuclear power plants nuclear power plants in the U.S. and about in the U.S. and about 435 worldwide.435 worldwide.

• 17% of the world’s 17% of the world’s energy comes from energy comes from nuclear.nuclear.

Figure 25.11: Diagram of a nuclear power plant.

A controlled fission chain reaction.

FissionFission• Advantages: is the

lack of air pollution.• Disadvantages:

include the risk of exposure & radioactive waste (takes hundreds of years to decay)

Harris plant, near Raleigh

Lake Harris

Nuclear Fusion

Fusion small nuclei combine

2H + 3H 4He + 1n + 1 1 2 0

Occurs in the sun and other stars

Energy

FUSION

• Fusion is the name given to the nuclear reaction whereby small nuclei are induced to join together into larger nuclei and release energy in the process.

• It is the reaction that "fuels" all stars including the Sun.

• A typical reaction that is taking place in the Sun is the fusion of two different isotopes of hydrogen to produce helium.

Nuclear Fusion

• 21H + 2

1H 42He + energy

• Two small, positively-charged nuclei smash together at high temperatures and pressures to form one larger nucleus.

• A small bit of mass is destroyed and converted into a huge amount of energy, more than even fission.

FusionFusion• We do not use fusion reactions for

energy b/c of the extremely high temperatures needed to start the reaction & because the plasma would need to be contained.

FISSION AND FUSIONFISSION AND FUSION

• Fission is the splitting of an atomic nucleus into two smaller parts

• Fusion is a process in which the nuclei of two atoms combine to form a larger nucleus

Nuclear Medicine: Nuclear Medicine: ImagingImaging

• Thyroid imaging using Iodine-131Thyroid imaging using Iodine-131• The radioisotope is used as a tracer.The radioisotope is used as a tracer.• Must have a short half-life & can be Must have a short half-life & can be

eliminated from the body quickly.eliminated from the body quickly.

Food Food IrradiationIrradiation

•Food can be irradiated with Food can be irradiated with rays from rays from 6060Co or Co or 137137Cs.Cs.•Irradiated milk has a shelf life of 3 mo. Irradiated milk has a shelf life of 3 mo. without refrigeration.without refrigeration.•USDA has approved irradiation of meats USDA has approved irradiation of meats and eggs.and eggs.

“Radura” US FDA

Nuclear Music

• Nuclear Power to the People• Natural Decay• One Half Life to Live