Nuclear Chemistry Chm Chapter 22

The Nucleus Remember that the nucleus is comprised of the two nucleons, protons and neutrons. The number of protons is the atomic number (Z) The number of protons and neutrons together is effectively the mass of the atom (A)

Isotopes (Nuclides) Different neutrons = different mass There are three naturally occurring isotopes of uranium: –Uranium-234 –Uranium-235 –Uranium-238

Nuclear Reactions: Reactions that take place in the nucleus of the atom.. Ex:

Nuclear Reactions Mass must be conserved = Law of Conservation of Mass Atomic Number must be conserved = Law of Conservation of Mass Larger nuclei can split into smaller Neutron can be a product

Radioactivity It is not uncommon for some nuclides of an element to be unstable, or radioactive. We refer to these as radionuclides.

Types of Radioactive Decay Alpha Decay Loss of an  -particle (a helium nucleus) He 4242 U  Th He

Types of Radioactive Decay Beta Decay Loss of a  -particle (a high energy electron)  0−10−1 e 0−10−1 or I Xe  + e 0−10−1

Types of Radioactive Decay Gamma Emission Loss of a  -ray high-energy radiation almost always accompanies the loss of a nuclear particle  0000

Penetrating Ability Alpha least penetrating –Cannot penetrate skin –Can cause damage to mucous membranes –Cannot penetrate paper Beta = 100x more penetrating than alpha –Can penetrate paper & skin –Cannot penetrate lead or glass Gamma most penetrating –Can penetrate paper, skin, lead, glass and concrete

Radiation Exposure rem – the quantity of radiation that does damage to human tissue. Avg. exposure = 0.1 rem/yr Max. dose = 0.5 rem/yr Exposure long-term or in high dose = cancer and genetic mutations Detector = Geiger-Müller Counters

Half Life (t 1/2 ) Time required for half of the atoms of a radioactive nuclide to decay. Ex: –Carbon-14 t 1/2 = 5, 715 yrs –Potassium-40t 1/2 = 1.3 x 10 9 yrs –Polonium – 218t 1/2 = 3.0 min –Uranium – 238t 1/2 = 4.46 x 10 9 yrs –Astatine – 218t 1/2 = 1.6 sec

Ex: pg 709 Phosphorus-32 has a half life of 14.3 days. How many milligrams of phosphorus-32 remain after 57.2 days if you start with a 4.0 mg sample?

Nuclear Fission Nuclear fission is the type of reaction carried out in nuclear reactors.

Nuclear Fission Radioactive nuclei bombarded with neutrons Neutrons released in reaction go on to bombard other radioactive nuclei This process continues in what we call a nuclear chain reaction. Fission = “splitting”

Nuclear Reactors Energy generated by fission = produces steam that turns a turbine connected to a generator.

Nuclear Fusion Fusion – “fusing” Happens naturally at the center of our sun Fusion would be a superior method of generating power. –MUCH more energy produced –Products of the reaction are not radioactive. –Material used must be in the plasma state –Materials not readily available = more expensive