Introduction to Nuclear Chemistry

Chapter 19

I. Study of Nuclear Reactions

Nuclear Reactions vs. Chemical ReactionsDefine “ Chemical Reaction”?

RnparticlealphaRa 22286

22688

Define “Nuclear Reaction”Reaction involving spontaneous emission of radiation by an unstable nuclei to a more stable nuclei of a different element.

Involves changes within nucleus.Atoms of each element do not balance.Spontaneous change of a radioisotope.

RnparticlealphaRa 22286

22688

RnparticlealphaRa 22286

22688

II. Types of Nuclear Radiation **Responsible for properties of top three!!

Example Nuclear Reactions:

RnRa 22286

42

22688 He

NpeU 23993

01-

23992

* 23090

00

23090 ThTh

Rules For Balancing Nuclear Reactions:

1. The sum of the mass numbers of the reactants must equal the sum of the mass number of the products.

*Total # nucleons remain the same.

2. The sum of the atomic numbers of the reactants must equal the sum of the mass number of the products.

* Electrical charge remains the same.

What kind of radiation is produced in the following nuclear reaction?

? 21884

22286 PoRn ? 218

8422286 PoRn

III. Radioactive Decay Rates

Follows First Order KineticsCommonly described by “half-life”.

t1/2

“The time required for half the radioactive atoms in a sample to undergo decay.”

Derived From Integrated Rate Law:

ktA

A

o

t-

][

][ln

ktoAtA

][

][ln kt

oAtA

][

][ln

kt0.693

2/1

Examples of Half-Lives

Iodine-131 (t1/2 = 8 days)

Example Problem:

The value of t1/2 for I-131 is 8 days.

How many I-131 atoms will remain after 24 days in a sample originally containing

6.4 x 1016 I-131 atoms?