Chapter 21: Nuclear Chemistry

Chemistry 1062: Principles of Chemistry II

Andy Aspaas, Instructor

Nuclear chemistry

• Chemical reactions where the nuclei change

• Independent of chemical surroundings (i.e. it doesn’t matter what compounds the nuclei are part of)

• Radioactive decay: unstable nuclei spontaneously disintegrate and give off radiation

• Nuclear bombardment reactions: one nucleus is physically struck by another nucleus to cause a nuclear reaction

Nuclear equations

• Nuclei only!

• Nuclide symbols used to show:

– Mass number, A– Atomic number, Z

• For particles with no protons, the atomic number represents the charge

– Ex. electron:

• Total mass numbers and atomic numbers must be equal on both sides of reaction

e01

Radioactivity

• Alpha emission: ejection of a helium-4 nucleus

– Occurs in nuclei where Z > 83 (transuranium)– Ex.

• Beta emission: ejection of a high-speed electron

– Occurs when N/Z is too large (N = # neutrons)– Ex.

He Ra Ra 42

22286

22688

e N C 01-

147

146

Radioactivity

• Positron emission: ejection of a positron

– Positron: positively charged particle with same mass as an electron

– Occurs when N/Z is too small– Ex.

• Electron capture: adding an electron to the nucleus

– Competes with positron emission when N/Z is too small– Ex.

e Mo Tc 01

9542

95 43

Ar e K 4018

01-

4019

Radiation

• Gamma emission: emission of a gamma photon from an excited state nucleus

– Metastable nucleus: excited nucleus a lifetime of at least one nanosecond

– Ex.

• Spontaneous fission: when a nucleus Z > 89 spontaneously breaks apart into other nuclei

– Ex.

γ Tc Tc 00

9943

9943 m

n 4 I Y U 10

13653

9639

23692

Predict the decay

• Predict the form of radioactive decay the following nuclei will have, and if possible, write a nuclear equation

BNp, Na, N, 85

24193

2611

137

Nuclear bombardment reactions

• Nuclei such as uranium-235 can be caused to split into several other nuclei if bombarded by a neutron

– Fission produces more neutrons, which can go on to cause other uranium nuclei to split

• The result is a chain reaction which releases the energy of neutron bombs and nuclear fission reactors

Nuclear fission reactor

• Pressurized light water reactor

• Most commondesign in US

• Prairie Island, MN

Prairie Island Nuclear Generating Plant, Red Wing, MN