chapter 25 nuclear chemistry i. the nucleus -terms (p. 798-820) i. the nucleus -terms (p. 798-820) i...

CHAPTER 25

Nuclear

Chemistry

CHAPTER 25

Nuclear

ChemistryI. The Nucleus -I. The Nucleus -

TermsTerms(p. 798-820)

I. The Nucleus -I. The Nucleus -TermsTerms

(p. 798-820)

I

IV

III

II

Ionizing RadiationIonizing RadiationIonizing RadiationIonizing Radiation

Radiation is a form of energy transferred by waves or atomic particles

Ionizing Radiation is any radiation with high enough energy to create ions (by knocking electrons out of atoms)like UV, X, gamma, and cosmic rays

There are both natural sources of radiation (unstable nuclei and stars) and human created sources

Zone of StabilityZone of StabilityZone of StabilityZone of Stability

Stable nuclei exist within the “zone of stability” seen on the graph…not always a 1:1 ratio of p+ to no

Outside this range, nuclei are unstable and will decay (disintegrate) into new nuclei

DefinitionsDefinitionsDefinitionsDefinitions

Nucleons = particles in nucleus (p+ and n0)Nuclide refers to the nucleus of an atomNuclear Reactions involve transmutation

where one element become another. Radioactive Decay is the when unstable

nuclei spontaneous lose energy by emitting ionizing particles; as this changes the nucleus of the atom, this also changes the type of element

Alpha Particle(Helium Nucleus)(4.00147 amu)

Alpha Decay ProcessAlpha Decay ProcessAlpha Decay ProcessAlpha Decay Process

Parent NuclideAm-241U-238Th-232Ra-226

Daughter NuclideNp-237Th-234Ra-228Rn-222

A. Mass DefectA. Mass DefectA. Mass DefectA. Mass Defect

The mass defect describes the mass lost during the formation of nuclei

Difference between the mass of an atom and the mass of its individual particles.

4.00260 amuMass of atom

4.03298 amuMass of particles

B. Nuclear Binding B. Nuclear Binding EnergyEnergy

B. Nuclear Binding B. Nuclear Binding EnergyEnergy

Energy released when a nucleus is formed from nucleons. This contributes to the loss in mass of nucleus, described by E = mc2.

High binding energy = stable nucleus.

E = mc2E: energy (J)m: mass defect (kg)c: speed of light

(3.00×108 m/s)

B. Nuclear Binding B. Nuclear Binding EnergyEnergy

B. Nuclear Binding B. Nuclear Binding EnergyEnergy

Unstable nuclides are radioactive and undergo radioactive decay.

Iron (Fe) is the most stable nucleus!!

CHAPTER 25

Nuclear

Chemistry

CHAPTER 25

Nuclear

ChemistryII. Radioactive II. Radioactive

DecayDecay(p. 798-820)

II. Radioactive II. Radioactive DecayDecay

(p. 798-820)

I

IV

III

II

He42

Types of Spontaneous Types of Spontaneous RadiationRadiation

Types of Spontaneous Types of Spontaneous RadiationRadiation

Alpha particle () helium nucleus paper2+

Beta particle or - electron

e0-1 1-

woodPositron +

positrone0

1 1+

Gamma () high-energy photon 0

Lead orconcrete

Greek symbol charge

stopped by…

γ00

p11

Other Radiation particlesOther Radiation particlesOther Radiation particlesOther Radiation particles

proton p++1

neutron n0

n10 0

Greek symbol charge

How does an electron get How does an electron get emitted from the nucleus?emitted from the nucleus?How does an electron get How does an electron get emitted from the nucleus?emitted from the nucleus?

Basically a neutron splits into a proton which stays in the nucleus and an electron is emitted ( decay)

n & p in nucleus

n is “really” like a p and e together

n converted to a proton and an e is emitted

+ ++ +

+-

-

Transmutation ReactionsTransmutation ReactionsTransmutation ReactionsTransmutation Reactions

I Alpha Emission

He Th U 42

23490

23892

parentnuclide

daughternuclide

alphaparticle

Numbers must balance on both sides of arrow!!238amu on left = (234 + 4amu)

92 is nucl chrg on left = 90 + 2 on right

B. Nuclear DecayB. Nuclear DecayB. Nuclear DecayB. Nuclear Decay

II Beta Emission

e Xe I 0-1

13154

13153

electron III Positron Emission

e Ar K 01

3818

3819

positron*a proton 1p is not the same as a positron 0e

B. Nuclear DecayB. Nuclear DecayB. Nuclear DecayB. Nuclear Decay

IV Electron Capture

Pd e Ag 10646

0-1

10647

electron

B. Nuclear DecayB. Nuclear DecayB. Nuclear DecayB. Nuclear Decay

V Alpha Capture followed by neutron emission

n Cl He P 10

3417

42

3115

Alpha captureGamma Emission causes no change in mass or charge and…

Usually follows the previous

types of decay.

γ00

Beta (Negatron) Decay ProcessBeta (Negatron) Decay ProcessBeta (Negatron) Decay ProcessBeta (Negatron) Decay Process

Parent NucleusRhenium-187Potassium-40

Daughter NucleusOsmium-187Calcium-40

Beta Particle(electron)

Antineutrino

Beta ParticlesBeta ParticlesBeta ParticlesBeta Particles

Same as an electron with kinetic energyPositive or negative charge of 1May be positively or negatively chargedCan normally be stopped by 1 cm of

plastic, wood, paper Exception for positron emitters

B. Nuclear DecayB. Nuclear DecayB. Nuclear DecayB. Nuclear Decay

Why nuclides decay…pg. 803 need stable ratio of neutrons to protons

He Th U 42

23490

23892

e Xe I 0-1

13154

13153

e Ar K 01

3818

3819

Pd e Ag 10646

0-1

10647

DECAY SERIES TRANSPARENCY

C. Half-lifeC. Half-lifeC. Half-lifeC. Half-life

Half-life (t½) Time required for half the atoms of a

radioactive nuclide to decay. Shorter half-life = less stable.

C. Half-lifeC. Half-lifeC. Half-lifeC. Half-life

nif mm )( 2

1

mf: final massmi: initial massn: # of half-lives

C. Half-lifeC. Half-lifeC. Half-lifeC. Half-life Fluorine-21 has a half-life of 5.0 seconds. If you start

with 25 g of fluorine-21, how many grams would remain after 60.0 s?

GIVEN:

t½ = 5.0 s

mi = 25 g

mf = ?

total time = 60.0 s

n = 60.0s ÷ 5.0s =12

WORK:

mf = mi (½)n

mf = (25 g)(0.5)12

mf = 0.0061 g

Decay SeriesDecay SeriesDecay SeriesDecay Series Many heavy elements Many heavy elements

are unstable and so are unstable and so they will continue to they will continue to decay (be radioactive) decay (be radioactive) until they finally until they finally transmute into a transmute into a stable nucleus.stable nucleus.

Here is an example of Here is an example of the Th-232 decay the Th-232 decay seriesseries

Thorium oxide is used Thorium oxide is used to in camping lanterns to in camping lanterns to intensify the to intensify the brightness when on brightness when on fire. fire.

Stable isotope