A X 14 N + 1 14 C 7 0 e 6 Conservation of mass = Conservation of - - PDF document

1 Nuclear Chemistry Topic 13.1

Radioactivity

• spontaneous decomposition of naturally occurring,

unstable isotopes

• forms a new element
• accompanied by the release of subatomic particles

and/or E

Nuclide = Nuclide =

A general term for an isotope of any element Can refer to isotopes of an element

Z A X

Isotopic notation Mass # Mass # Nuclear Nuclear charge charge

6 13C 6 14C

Nuclear equations 6 14C → 7 14N + −1 0e Conservation of mass = Conservation of mass = Conservation of charge = Conservation of charge =

Sums of mass #s of each side must equal Sums of charges on each side must equal Radioactive elements include all those whose nuclei contain more than ______ protons

83

Which naturally occurring element contains the greatest number of protons? U

5 types of radioactive decay: 1.Alpha particle production 2.Beta particle production 3.Gamma ray production 4.Positron production 5.Electron capture

2

Types of radioactive decay:

92 238U 2 4He

He +

90 234Th

• 1. alpha particle:

an element spontaneously releases a helium nucleus with no electrons

2 4He +2

(α) or

What happens to ratio of n0/p /p+ ? ? ↑ ratio: from 146/92 to 144/90

88 226Ra

90

230Th + 2 4He 82 214Pb 84 218Po + 2 4He

• 2. Beta particle production (β or e-)

an element releases an e- and gains a p+

• a neutron splits into a p+ and an e-
• the e- is released

90

234Th 91 234Pa

Pa +

1 0e

What happens to ratio of n0/p+ ? ↓ratio: from 144/90 to 143/91

91

234Pa

+ 1

0e 92 234U 82 210Pb

+ 1

0e 83 210Bi

• very high E photon of nonvisible light
• Unstable nuclide has too much energy

(excited state)

• Excess E can be released by producing

γ-rays

• This often accompanies other forms
• f nuclear decay
• 3. Gamma rays (γ)

92 238U 2 4He + 90 234Th + 20

no change of mass or nuclear charge Excited nucleus ground state nucleus + 0 (excess energy) (lower energy)

3

• same mass as electron
• pposite charge (anti-electron)

11 22Na How:

• p+ decays into a n0 and β+,

, β+

+ emitted

1 0e

• 4. Positron emission (β+ or )

What happens to ratio of n0/p+ ? ↑ ratio: from 11/11 to 12/10

10 22Ne

Ne + 1

0e 6 11C + 1 0e 5 11B 53 118I 54 118Xe + 1 0e

• an inner shell e- is pulled into nucleus
• merges with a p+ to form a n0
• Always accompanied by γ-rays

80 201Hg + 1 0e

• 5. Electron capture

What happens to ratio of n0/p+ ? ↑ ratio: from 121/80 to 122/79

79 201Au

Au + 0

33 73As + 1 0e 84 204Po + 1 0e 32 73Ge

e + 0

83 204Bi

Bi+ 0

+1

• 1

+1

• 1
• 1

+1

• 2
• 4
• 2

e-

capture

β+

emission

γ

emission

β

emission

α

emission Change in # n0 Change in mass

Change in nuclear charge

symbol process 2 4He

• 1

0 e +1 0 e

• 1

0 e

• 1. Alpha emission from Cm-242
• 2. Alpha emission from Np-237
• 3. Beta emission from Mg-28
• 4. Beta emission from Ru-106
• 5. Positron emission from N-13
• 6. Positron emission from Ta-165
• 7. Electron capture of Sm-138
• 8. Electron capture of Ar-36

4

Write nuclear equations for the following processes:

Alpha emission from Cm-242 Alpha emission from Np-237 96 242Cm 93 237Np 94 238Pu + 2 4He 91 233Pa + 2 4He Beta emission from Mg-28 Beta emission from Ru-106

12 28Mg 44 106Ru 13 28Al

Al + 1

0e 45 106Rh

Rh + 1

0e

Positron emission from N-13 Positron emission from Ta-165

73

165Ta 7 13N 6 13C

C + 1

0e 72 165Hf

Hf + 1

0e Electron capture of Sm-138 Electron capture of Ar-36 62 138Sm 18 36Ar

Sm + 1

0e 61 138Pm+ 0

Ar + 1

0e 17 36Cl

Cl + 0

Write the nuclear equation that represents the fusion of He-3 with H-1 to yield a positron, a gamma ray and one additional product.

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