Nuclear ChemistryChm 1.1.4 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)

He42

U23892

Th23490 He4

2+

Types of Radioactive Decay Beta Decay

Loss of a -particle (a high energy electron)

0−1 e0

−1or

I13153 Xe131

54 + e0

−1

Types of Radioactive Decay Gamma Emission

Loss of a -ray

high-energy radiation

almost always accompanies the loss of a nuclear particle

00

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 (t1/2)

• Time required for half of the atoms of a radioactive nuclide to decay.

• Ex: – Carbon-14 t1/2 = 5, 715 yrs

– Potassium-40 t1/2 = 1.3 x 109 yrs

– Polonium – 218 t1/2 = 3.0 min

– Uranium – 238 t1/2 = 4.46 x 109 yrs

– Astatine – 218 t1/2 = 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