NUCLEAR CHEMISTRY

Discovery of Radiation

Roentgen (1895)

•Discovered a mysterious form of radiation was given off even without electron beam. This radiation could pass through paper and other objects but not dense materials (lead, bone).

•Called them X-rays

•Studied fluorescent materials that glowed when hit with a beam of electrons.

Becquerel (1896)•Studied fluorescent minerals containing uranium.•Discovered radioactivity by accident on a cloudy day:•Thought that an external source was needed to produce the mysterious radiation.

•Found that uranium emits radiation without external source.

Thought radioactivity was a property of heavy elements.

Pierre and Marie Curie

During study, discovered new radioactive elements: Polonium and Radium.

Wondered how small mass can give off large amount of energy:

Explained by Einstein with E=mc2.

•Studied radioactivity and named types of nuclear radiation.

Rutherford

•Discovered that elements decay into other elements after emitting nuclear radiation. Called it Nuclear Decay.•Gold foil experiment revealed that the mass of an atom is concentrated in the nucleus (atom is mostly space)

Atomic StructureRecall:Atoms – consist of a positively charged nucleus, which has protons and neutrons.

Isotope Symbol # protons # neutrons

Atomic Mass

Mo-101

H-2

C-14

U-238

Bi-210

He-4

H21C146U238

92

Bi21083

He42

Mo10142 42

1

6

92

83

2

59

1

8

146

127

2

101

2

14

238

210

4

Isotope – atoms of the same chemical element that have a different number of neutrons. Each isotope of a given element is designated by the total number of its protons plus its neutrons.

Nuclear Forces1. Electric repulsion – ________ charge particles

repel each othersame

2. Strong Nuclear Force – causes protons and neutrons to ________ each otherattract

•Stable Nuclei = strong nuclear force is ________ than repulsion force

greater

•Unstable Nuclei = strong nuclear force is ________ than repulsion force

oHave too many or too few neutrons in nucleusoHave more than 83 protons in nucleusoWill undergo radioactive decay to form a more stable nucleus

less

Nuclear Decay• Why nuclides decay

– 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

•Transmutation-One element becomes another.

More than 83 protons means that the nuclei is unstable (radioactive)

He42

Types of Radiation

• Alpha particle ()– helium nucleus paper2+

• Beta particle (-)– electron

e0-1 1-

lead

• Positron (+)– positron

e01 1+

• Gamma ()– high-energy photon 0 concrete

ChargeShielding

00

Penetrating Ability of Radiation

Alpha Emission

He Th U 42

23490

23892

parentnuclide

daughternuclide

alphaparticle

Numbers must balance!!

occurs when the nucleus has too many protons which cause excessive repulsion.

Alpha Emission

U23592Pu239

94 He42

Ex. Plutonium-239 undergoes alpha decay

+

239

Atomic Mass: = 235

4+

94Atomic #: = 92 2+

Masses must be equal = Conservation of mass

XAZPo21084 He4

2

Ex. Polonium-210 undergoes alpha decay to produce this daughter nuclide

+

Alpha Emission

Atomic Mass: 210

= A 4+

Atomic #: 84 = Z 2+

210

= A4- = 206

84 = Z2- = 82

XAZ = Pb20682

Beta Emission

e Xe I 0-1

13154

13153

electron

occurs when the neutron to proton ratio is too great.

XAZPo21084

Ex. Polonium-210 undergoes beta decay to produce this daughter nuclide

+

Beta Emission

Atomic Mass: 210

= A 0+

Atomic #: 84 = Z -1+

210

= A0- = 210

84 = Z1+ = 85

XAZ = At21085

e01-

e Ar K 01

3818

3819

positron

Positron EmissionOccurs when the neutron to proton ratio is too small.

XAZPo21084

Ex. Polonium-210 undergoes positron emission to produce this daughter nuclide

+

Positron Emission

Atomic Mass: 210

= A 0+

Atomic #: 84 = Z +1+

210

= A0- = 210

84 = Z1- = 83

XAZ = Bi21083

e01

Electron Capture

Pd e Ag 10646

0-1

10647

electron

occurs when the neutron to proton ratio in the nucleus is too small.

XAZPo21084

Ex. Polonium-210 captures an electron to produce this daughter nuclide

+

Electron Capture

Atomic Mass: 210

= A0+

Atomic #: 84 = Z-1+

A = 210

Z = 83

XAZ = Bi21083

e01-

Gamma Emission

– Emission of high energy electromagnetic wave.

occurs when the nucleus is at too high an energy.

XAZPo21084

Ex. Polonium-210 undergoes gamma decay to produce this daughter nuclide

+

Gamma Emission

Atomic Mass: 210

= A 0+

Atomic #: 84 = Z 0+

A = 210

Z = 84

XAZ =

00

Po21084

Write Nuclear Equations!

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