1

NUCLEAR CHEMISTRY

2IsotopesIsotopes

• Same element (Same element (ZZ) but different mass ) but different mass number (number (AA).).

• Boron-10Boron-10 has has 5 p5 p and 5 n: and 5 n: 101055BB

• Boron-11Boron-11 has has 5 p5 p and 6 n: and 6 n: 111155BB

10B

11B

3IsotopesIsotopes• Hydrogen: Hydrogen:

– 1111H, protiumH, protium

– 2211H, deuteriumH, deuterium

– 3311H, tritium H, tritium

(radioactive)(radioactive)

• Helium, Helium, 4422HeHe

• Lithium, Lithium, 6633Li Li

and and 7733LiLi

• Boron, Boron, 101055B B

and and 111155BB

• Except for Except for 1111H the mass H the mass

number is always at least 2 number is always at least 2

x atomic number. x atomic number.

• Repulsive forces between Repulsive forces between

protons must be protons must be

moderated by neutrons.moderated by neutrons.

4ATOMIC COMPOSITIONATOMIC COMPOSITION

• ProtonsProtons– + electrical charge+ electrical charge– mass = 1.672623 x 10mass = 1.672623 x 10-24-24 g g– relative mass = 1.007 atomic mass units relative mass = 1.007 atomic mass units

(amu)(amu)• ElectronsElectrons

– negative electrical chargenegative electrical charge– relative mass = 0.0005 amurelative mass = 0.0005 amu

• NeutronsNeutrons– no electrical chargeno electrical charge– mass = 1.009 amumass = 1.009 amu

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RadioactivityRadioactivity

• One of the pieces of evidence for One of the pieces of evidence for the fact that atoms are made of the fact that atoms are made of smaller particles came from the smaller particles came from the

work of work of Marie CurieMarie Curie (1876- (1876-1934). 1934).

• She discovered She discovered

radioactivityradioactivity, the , the spontaneous disintegration of some spontaneous disintegration of some elements into smaller pieces.elements into smaller pieces.

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RadioactivityRadioactivity Emission of particles and/or

energy due to a change in the nucleus of an atom.

Nuclear Radiation also called Ionizing radiation

Measure with Geiger Counter

7Geiger Counter: Geiger Counter:

Radiation detectionRadiation detection

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Types of NUCLEAR Types of NUCLEAR RadiationRadiation

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Nuclear ReactionsNuclear Reactions

• Ernest Rutherford found Ra forms Rn gas

when emitting an alpha particle.

• 1902—Rutherford and Soddy proposed

radioactivity is the result of the natural

change of the isotope of one element into

an isotope of a different element.

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Nuclear ReactionsNuclear ReactionsorTransmutationsorTransmutationsNatural Decay

Spontaneous breakdown of unstable nuclei.

Called Radioisotopes

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Penetrating AbilityPenetrating Ability

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NATURAL Decay:NATURAL Decay:

DECAY = Fall apartAlpha DECAYBeta DECAY

Positon DECAY

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Nuclear ReactionsNuclear Reactions• Alpha emissionAlpha emission

Note that mass number (A) goes down by 4 and atomic number (Z) goes down by 2.

Nucleons are rearranged but conserved [mass number (A)]

Nucleons = PROTON OR NEUTRON (particle in the nucleus)

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Nuclear ReactionsNuclear Reactions• Beta emissionBeta emission

Note that mass number (A) is unchanged and atomic number (Z) goes up by 1.

How does this happen?

15Other Types of Nuclear Other Types of Nuclear ReactionsReactions

Positron (Positron (00+1+1): a positive electron): a positive electron

K-capture:K-capture: the capture of an electron from the first or K shell

An electron and proton combine to form a neutron.0

-1e + 11p --> 1

0n

207 207

16Radioactive Decay SeriesRadioactive Decay Series

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Writing Nuclear Reactions Parent element = Reactant

Daughter element = Product

Radioactivity = radiation produced

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Writing Nuclear Reactions

Law of Conservation of Mass

L. of C. of Charge Isotopic Notation Mass # and Nuclear Charge

146C = 14

7N + 0-1e

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21Stability Stability of of NucleiNuclei

• Heaviest naturally Heaviest naturally

occurring non-radioactive occurring non-radioactive

isotope is isotope is 209209Bi with 83 Bi with 83

protons and 126 neutronsprotons and 126 neutrons

• There are 83 x 126 = There are 83 x 126 =

10,458 possible isotopes. 10,458 possible isotopes.

Why so few actually exist?Why so few actually exist?

22Band of Stability Band of Stability and Radioactive and Radioactive DecayDecay 243

95Am --> 42 + 239

93Np

emission reduces Z

emission increases Z

6027Co --> 0

-1 + 6028Ni

Isotopes with low n/p ratio, below band of stability decay, by positron emission or electron capture

23Stability Stability of of NucleiNuclei

• Out of > 300 stable isotopes:

EvenEven OddOdd

OddOdd

EvenEven

ZZNN

157157 5252

5050 55

31311515PP

191999FF

2211H, H, 66

33Li, Li, 101055B, B, 1414

77N, N, 1801807373TaTa

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Binding Energy, EBinding Energy, Ebb

EEbb = energy required to separate the = energy required to separate the

nucleus into protons and neutronsnucleus into protons and neutrons..

For deuterium, For deuterium, 2211HH

2211H ---> H ---> 11

11p + p + 1100nn EEbb = 2.15 x 10 = 2.15 x 1088 kJ/mol kJ/mol

EEbb per nucleon per nucleon = = EEbb //2 2 nucleonsnucleons

= 1.08 x 10= 1.08 x 1088 kJ/mol nucleons kJ/mol nucleons

25Binding Binding Energy/NucleonEnergy/Nucleon

26Calculate Binding Calculate Binding EnergyEnergy

For deuterium, For deuterium, 2211H: H: 22

11H ---> H ---> 1111p + p + 11

00nn

Mass of Mass of 2211H = 2.01410 g/molH = 2.01410 g/mol

Mass of proton = 1.007825 g/molMass of proton = 1.007825 g/mol

Mass of neutron = 1/008665 g/molMass of neutron = 1/008665 g/mol

∆∆m = 0.00239 g/molm = 0.00239 g/mol

From Einstein’s equation: From Einstein’s equation:

EEbb = (∆m)c = (∆m)c22 = 2.15 x 10 = 2.15 x 1088 kJ/mol kJ/mol

EEbb per nucleon = E per nucleon = Ebb/2 nucleons /2 nucleons

= 1.08 x 10= 1.08 x 1088 kJ/mol nucleons kJ/mol nucleons

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Half-LifeHalf-LifeSection 15.4 & Screen 15.8Section 15.4 & Screen 15.8

• HALF-LIFEHALF-LIFE is the time it takes for 1/2 a is the time it takes for 1/2 a sample is disappear.sample is disappear.

• The rate of a nuclear transformation depends The rate of a nuclear transformation depends only on the “reactant” concentration.only on the “reactant” concentration.

• Concept of HALF-LIFE is especially useful for Concept of HALF-LIFE is especially useful for 1st order reactions.1st order reactions.

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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?

29Kinetics of Radioactive Kinetics of Radioactive DecayDecay

Activity (A) = Disintegrations/time = (k)(N)

where N is the number of atoms

Decay is first order, and so

ln (A/Ao) = -kt

The half-life of

radioactive decay is

t1/2 = 0.693/k