Nuclear ChemistryNuclear Chemistry

TermsTerms

RadioactivityRadioactivity Property of certain unstable nuclide Property of certain unstable nuclide

of spontaneously emitting radiations of spontaneously emitting radiations in order to form more stable species.in order to form more stable species.

Nuclide --> used in place of the term Nuclide --> used in place of the term nucleusnucleus

Any atom having a nucleus of mass Any atom having a nucleus of mass number A, atomic number Z and number A, atomic number Z and number of neutrons N number of neutrons N AA

ZZ XXnn

IsotopesIsotopes Atoms of the same element having Atoms of the same element having

different atomic massesdifferent atomic masses

11HH00 22 H H11 33HH22

Some isotopes are unstable that Some isotopes are unstable that undergoes spontaneous emission of undergoes spontaneous emission of radiationradiation

Unstable nucleiUnstable nuclei Are called radioactive isotopes or Are called radioactive isotopes or

radioisotopesradioisotopes

What are the particles that make up the What are the particles that make up the nucleus? nucleus?

Protons and neutrons ( nucleons)Protons and neutrons ( nucleons)

Radioactive DecayRadioactive Decay

Alpha,beta, and gamma decayAlpha,beta, and gamma decay

Alpha DecayAlpha Decay

a mode of decay in which the mass a mode of decay in which the mass number changesnumber changes

Alpha is a helium particleAlpha is a helium particle 44

He .He .22

Formula:Formula:

Parent --> alpha decay + daughter nucleusParent --> alpha decay + daughter nucleus

AA P ----> P ----> 44 He + He + A-4A-4 D D . . Z 2 Z-2Z 2 Z-2

Example:Example:

238238U ----> _______ + _______ U ----> _______ + _______ . .9292

------> 4------> 4He + He + 238-4238-4 X . X .

22 92-292-2

----> 4 He ----> 4 He ++ 234 234 XX

22 9090

-----> 4-----> 4HeHe + 234 Th + 234 Th

2 902 90

ExerciseExercise

1. 1. 210210 Po -----> _______, ______ Po -----> _______, ______

8484

2.2. 219 219 Rn ---> _____, ______ Rn ---> _____, ______ . . 8686

Beta DecayBeta Decay

An emission of an electron from the An emission of an electron from the nucleusnucleus

AAP ----> P ----> A A D + D + 00e e z z+1 -1z z+1 -1

Positron DecayPositron Decay

AAP ----> P ----> A A D + D + 00e e z z-1 +1z z-1 +1

What happens to the nucleus What happens to the nucleus when it emits beta particles?when it emits beta particles?

A A P ------> P ------> AA D D 0 0 e . e . .. Z+1 -1Z+1 -1

Ex: Ex: 40 40 K ----> K ----> 4040 Ca + Ca + 0 0 ee

19 20 -119 20 -1

Positron DecayPositron DecayPositron DecayPositron Decay

AAP ----> P ----> A A D + D + 00e e z z-1 +1z z-1 +1

Nitrogen 12 after emitting a Nitrogen 12 after emitting a positron becomes carbon 12positron becomes carbon 12

1212N -------> 12C + N -------> 12C + 0 0 e e . .77 6 +16 +1

Complete the ff nuclear reactions:Complete the ff nuclear reactions:1.1. _____ ---> _____ ---> 3030Si + Si + 00e e

. . 14 +114 +1

2.2. 14 14 O ------>O ------>1414 N + ____ N + ____

PracticePractice

Complete the ff nuclear reactions:Complete the ff nuclear reactions:

1.1. _____ ---> _____ ---> 3030Si + Si + 00e e . . 14 14

+1+1

2.2. 14 14 O ------>O ------>1414 N + ____ N + ____

ExercisesExercises

Complete the following nuclear Complete the following nuclear reactionsreactions

a)a) 1414 C ---> _______ + C ---> _______ + 0 0

e . e . 66 --

11

b)b) 30 30 AlAl --->---> _____________ + 0 _____________ + 0 e e 13 -113 -1

Electron-captureElectron-capture

Is a process in which one of the Is a process in which one of the inner orbital electrons is captured by inner orbital electrons is captured by the nucleusthe nucleus

Results in a decrease in Z-number of Results in a decrease in Z-number of the daughter nucleus and no change the daughter nucleus and no change in A-numberin A-number

Ex: Ex: 201201Hg + Hg + 00e ---> e ---> 201201Au + gamma raysAu + gamma rays

8080 -1-1 7979

Write the nuclear reaction Write the nuclear reaction involved when Ba-133 captures involved when Ba-133 captures an orbital electronan orbital electron

133133Ba + Ba + 00 e = _____ + _____ e = _____ + _____

5656 -1-1

133133Cs + X-raysCs + X-rays

5555

Gamma DecayGamma Decay

Gamma Rays are high energy Gamma Rays are high energy radiation similar to X-Raysradiation similar to X-Rays

mass number and atomic number of mass number and atomic number of the nucleus remains the samethe nucleus remains the same

Only energy changesOnly energy changes

6060Co -------->Co -------->6060 Co + gamma rays Co + gamma rays

2727 2727

What is the difference between What is the difference between gamma rays, x-rays and visible gamma rays, x-rays and visible light? light? Gamma rays is identical to x-rays Gamma rays is identical to x-rays

except that it originates from the except that it originates from the nucleinuclei

X-rays and visible light rays originate X-rays and visible light rays originate in the electron shell of the atomin the electron shell of the atom

RayRay Charge NatureCharge Nature Penetrating Penetrating PowerPower

AlphaAlpha Helium ionHelium ion Has very low Has very low penetrating- can penetrating- can be stopped by a be stopped by a paperpaper

BetaBeta electronelectron Slight Slight penetrating –can penetrating –can be stopped by a be stopped by a thin sheet of Althin sheet of Al

GammaGamma No charge No charge behaves like an behaves like an x-rayx-ray

Very penetratingVery penetrating

Needs a thick Needs a thick sheet of lead to sheet of lead to stopstop

Half LifeHalf Life

Time required for half of the nuclei in a Time required for half of the nuclei in a sample to undergo radioactive decaysample to undergo radioactive decay

Ex: Thorium-234 has a half life of 24 days. Ex: Thorium-234 has a half life of 24 days. Suppose you have 1 gram sample,what Suppose you have 1 gram sample,what fraction exist after 3 half lives? Four half fraction exist after 3 half lives? Four half lives? Five half lives?lives? Five half lives?

Time # of t= ½ amt. RemainingTime # of t= ½ amt. Remaining 0 10 124 1 1/224 1 1/248 2 1/448 2 1/472 3 1/8 72 3 1/8 96 4 1/16 96 4 1/16

ExerciseExercise

strontium-90 has a half life of 28 years. If strontium-90 has a half life of 28 years. If we have 60g of strontium 90 today, how we have 60g of strontium 90 today, how many grams will be left after 56 years? 84 many grams will be left after 56 years? 84 years later?years later?

H-3 has a half life of 12.46 years. How long H-3 has a half life of 12.46 years. How long must a sample be stored so that only ¼ of must a sample be stored so that only ¼ of the original is left?the original is left?

The half life of radon 222 is 4 days. If you The half life of radon 222 is 4 days. If you start with 5.o g how much will be left in 16 start with 5.o g how much will be left in 16 days?days?

Why are some nuclie stable and Why are some nuclie stable and others are unstable?others are unstable?

Nuclear StabilityNuclear Stability

Stability of isotopes is based Stability of isotopes is based on the ratio of neutrons and on the ratio of neutrons and protons in a nucleus.protons in a nucleus.

Stable Stable n/p = 1 n/p = 1Generally, ratio between 1-1.6 is stable Generally, ratio between 1-1.6 is stable

Ex: stable nucleiEx: stable nuclei Carbon 12 -Carbon 12 - p = ? n =? p = ? n =?

p = 6 n = 6p = 6 n = 6

n/p = 1n/p = 1 Pb-206 -Pb-206 - p = ? n =? p = ? n =?

p = 82 n =124p = 82 n =124

n/p = 124/82 = 1.5 n/p = 124/82 = 1.5

Example of unstable nucleiExample of unstable nuclei

H-3 -------> p= ? n=?H-3 -------> p= ? n=?

p= 1 n = 2p= 1 n = 2

n/p = 2n/p = 2

2 is more than 1.6 so it is unstable2 is more than 1.6 so it is unstable

S -31 ------> p = ? n =?S -31 ------> p = ? n =?

p = 16 n = 15p = 16 n = 15

n/p = 15/16 = 0.94n/p = 15/16 = 0.94

Note:Note:

elements with atomic # >83 have no elements with atomic # >83 have no stable isotopes because 83 is the stable isotopes because 83 is the highest # of protons that can be highest # of protons that can be accommodated in a stable nucleusaccommodated in a stable nucleus

Odd-Even number of the nucleus also Odd-Even number of the nucleus also plays an important role in the stability plays an important role in the stability of the nucleiof the nuclei

even # of protons and neutrons even # of protons and neutrons are most stableare most stable

Odd # of protons and neutrons Odd # of protons and neutrons are least stableare least stable

Even-odd # of protons and Even-odd # of protons and neutrons are intermediateneutrons are intermediate

ExerciseExercise

Based on the ideas presented, can you Based on the ideas presented, can you predict which nuclei is stable? predict which nuclei is stable? unstable/radioactive? Explain your unstable/radioactive? Explain your answeranswer

a)a) Pb- 208Pb- 208

b)b) Ca-40Ca-40

c)c) As-76As-76

Radiocarbon DatingRadiocarbon Dating

Every living things contain carbon. Every living things contain carbon. There are two kinds of Carbon, There are two kinds of Carbon,

carbon-12 and carbon-14carbon-12 and carbon-14 Carbon14 is radioactiveCarbon14 is radioactive Living organisms have the same Living organisms have the same

amount of carbon-14. But when it amount of carbon-14. But when it dies it stop taking in carbon-14dies it stop taking in carbon-14

Age of certain fossil is determined by Age of certain fossil is determined by how much carbon-14 is lefthow much carbon-14 is left

Radiocarbon DatingRadiocarbon Dating Method used to determine the ages of Method used to determine the ages of

materials which were once livingmaterials which were once living It is based on the radioactivity of carbon-14 It is based on the radioactivity of carbon-14

which decays by beta particle productionwhich decays by beta particle production

1414C ----> C ----> 00e + e + 1414N N . . 66 -1-1 77

1414N + N + 11n -----> n -----> 1414C + C + 11H H 77 00 6 6 11

Carbon half-life is 5730 yearsCarbon half-life is 5730 years

Applications of Applications of

RadioactivityRadioactivity

What makes radioisotopes useful What makes radioisotopes useful in diagnostic procedure?in diagnostic procedure?

Ex: Iodine131 is used as Ex: Iodine131 is used as therapy for hyperthyroidismtherapy for hyperthyroidism

The radiation destroys the fast The radiation destroys the fast growing cells in the thyroid growing cells in the thyroid glandgland

Common radioisotopes in Common radioisotopes in Medical TechnologyMedical Technology Arsenic-74 Arsenic-74

locates brain tumorlocates brain tumor Iodine 131Iodine 131

detects thyroid malfunctiondetects thyroid malfunction Radium 226Radium 226

Used for radiation therapy for cancerUsed for radiation therapy for cancer Cobalt-60Cobalt-60

detect and treat tumorsdetect and treat tumors

Medical ApplicationMedical Application

RadiotracersRadiotracers

Radioactive nuclide that can be Radioactive nuclide that can be introduced into organisms in introduced into organisms in food or drugs and subsequently food or drugs and subsequently traced by monitoring their traced by monitoring their radioactivityradioactivity

Other Uses of RadioisotopesOther Uses of Radioisotopes

Producing weapons of warProducing weapons of war

Irradiation of food for Irradiation of food for preservationpreservation

Nuclear Power for electricityNuclear Power for electricity

Nuclear Power for electricityNuclear Power for electricity

Generating electricity from the Generating electricity from the nucleus of the atom.nucleus of the atom.

Nuclear disasters caused Nuclear disasters caused doubts on the advantages of doubts on the advantages of nuclear energy.nuclear energy.

Producing WeaponsProducing Weapons

Atomic BombsAtomic Bombs Was dropped in JapanWas dropped in Japan Causing death and destructionCausing death and destruction

Hydrogen BombsHydrogen Bombs

Irradiation of food for Irradiation of food for preservationpreservation Studies shows that when food products Studies shows that when food products

were processed through controlled doses were processed through controlled doses of x-rays or gamma rays the ff: were of x-rays or gamma rays the ff: were observed:observed:

Low dosage: kills any insects that remain Low dosage: kills any insects that remain after harvestafter harvest

Medium dosage: reduces the population of Medium dosage: reduces the population of salmonella bacteria in fish, poultry and salmonella bacteria in fish, poultry and other meatsother meats

High dosage: sterilizes poultry and other High dosage: sterilizes poultry and other meatsmeats