Transcript Nuclear Chemistry PPT

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 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)
4
2
238
92
U

He
234
90
4
2
Th+ He
Types of Radioactive Decay
Beta Decay
Loss of a -particle (a high energy electron)
0
−1
131
53
I

0
or −1
131

54
e
Xe
+
0
−1
e
Types of Radioactive Decay
Gamma Emission
Loss of a -ray
high-energy radiation
almost always accompanies the loss of a
nuclear particle
0
0

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
– Potassium-40
– Polonium – 218
– Uranium – 238
– Astatine – 218
t1/2 = 5, 715 yrs
t1/2 = 1.3 x 109 yrs
t1/2 = 3.0 min
t1/2 = 4.46 x 109 yrs
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