C. Johannesson

CHAPTER 22

Nuclear

Chemistry

CHAPTER 22

Nuclear

ChemistryII. Radioactive II. Radioactive

DecayDecay(p. 705 - 712)

II. Radioactive II. Radioactive DecayDecay

(p. 705 - 712)

I

IV

III

II

C. Johannesson

He42

A. Types of RadiationA. Types of RadiationA. Types of RadiationA. Types of Radiation

Alpha particle () helium nucleus paper2+

Beta particle (-) electron e0

-11-

leadPositron (+)

positron e01

1+

Gamma () high-energy photon 0

concrete

C. Johannesson

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

Alpha Emission

He Th U 42

23490

23892

parentnuclide

daughternuclide

alphaparticle

Numbers must balance!!

C. Johannesson

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

Beta Emission

e Xe I 0-1

13154

13153

electronPositron Emission

e Ar K 01

3818

3819

positron

C. Johannesson

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

Electron Capture

Pd e Ag 10646

0-1

10647

electronGamma Emission

Usually follows other types of decay.

Transmutation One element becomes another.

C. Johannesson

B. Nuclear DecayB. Nuclear DecayB. Nuclear DecayB. 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

DECAY SERIES TRANSPARENCY

C. Johannesson

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. Johannesson

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

nif mm )( 2

1

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

C. Johannesson

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