Nuclear Chemistry Chm 1.1.4 Chapter 22. The Nucleus Remember that the nucleus is comprised of the two nucleons, protons and neutrons. The number of protons.

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