Nuclear Chemistry

September 21, 2009Trianna McCall

Nuclear Reactions

• Nuclear chemistry is the study of changes in an atoms nucleus.

• Reactions that involve a change in the nucleus of an atom are called nuclear reactions.

Characteristics of Nuclear Reactions

• Occur when nuclei emit particles and/or rays• Atoms are often converted into atoms of

another element• May involve protons, neutrons, and electrons• Associated with large energy changes• Reaction rates aren’t normally affected by

temperature, pressure, or catalyst

Table 25-1 (p805 of textbook)

What Causes Nuclear Reactions?• The nuclei of some atoms are

unstable and may undergo several changes.

• Unstable systems gain stability by losing energy.

• Certain atoms lose energy by emitting rays and particles called radiation.

Related Terms

• This spontaneous emission of radiation is a process called radioactivity.

• The process by which unstable nuclei emit radiation to lose energy is called radioactive decay.

• Radioisotopes, isotopes of atoms with unstable nuclei, undergo nuclear decay.

Types of Radiation

• Alpha-Composed of alpha particles-Contains 2p+ and 2n⁰-4

2He• Beta

-Composed of beta particles-Fast moving e- - 0

-1β or 0-1e

Types of Radiation (cont)

• Gamma-Not deflected by electric or magnetic fields-No charge-0

0γ• http://www.mhhe.com/physsci/chemistry/ess

entialchemistry/flash/radioa7.swf

Types of Radiation SummaryType of

RadiationSymbol Charge Penetration

AbilityMass

alpha 42He 2+ blocked by

paperheaviest(4 amu)

beta 0-1β 1- blocked by

metal foillightest(1/1840 amu)

gamma 00γ 0 not completely

blocked by lead or concrete

none

Nuclear Equations

• Used to express nuclear reactions• Both sides of the equation must have an equal

sum of atomic mass and atomic numbers• Examples:

- 23592U ______________ + 231

90Th

- 37K 0e + ______________- 41Ca Ca + 0 _________________

Half-Life

• The time required for one half of a radioisotope’s nuclei to decay into its products is called a half-life.

• Amt Remaining=(Initial Amt)(1/2)n

-n = # half lives passed• Amt Remaining=(Initial Amt)(1/2)t/T

-t=elapsed time-T=duration of half life

Half-Life (cont)• Example half-life problems:

- How much of a 100.0g sample of 198Au is left after 8.10 days if its half-life is 2.70 days?

-A 50.0g sample of 16N decays to 12.5g in 14.4 seconds. What is its half-life?

-The half-life of 42K is 12.4hours. How much of a 750g sample is left after 62.0hours?

-What is the half-life of 99Tc if a 500g sample decays to 62.5 g in 639,000 years?

Fission and Fusion• The splitting of an atoms nucleus into

fragments is called fission.-Provides energy for nuclear power

plants• http://www.visionlearning.com/library/flash_v

iewer.php?oid=2391&mid=59• The combining of atomic nuclei is called

fusion.-Fuels the sun

• http://www.visionlearning.com/library/flash_viewer.php?oid=2747&mid=59