3 Nuclear Chemistry
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Genesis of the elements: The Big Bang??? t1/2 = 11.3 min
1.8 x 1010 years ago ~0 V αT
where:
universe after 1 s
Few minutes later, after T dropped to 109 K The limiting reaction; the reverse reaction is also fast The interplay of the rates gives an atomic ratio of H/He = 10/1 Sun
Within 11.3 min, half the matter of the universe consisted of protons; the temperature was about 5 x 108 K. In the first 30 to 60 min, 2H, 3He, 4He, and 5He were formed. These nuclei were formed in the process called hydrogen burning.
In stars, with T at 107 to 108 K, production of heavier nuclei occurred. Among known reactions that take place under such conditions are called helium burning.
In more massive stars (T at 6 x 108 K or higher), the C-N cycle is possible:
Heavier elements were formed as shown:
At still higher temperatures, further reactions take place:
Formation of elements of higher atomic number takes place by addition of neutrons to a nucleus followed by electron emission decay. 56 26
!
1 0
69 26
69 27
0 #1
Fe + 13 n" Fe" Co+ e
In environments of low neutron density, the addition of neutron is very slow, one neutron at a time; in high neutron density, 10 to 15 neutrons may be added in a very short time. The very heavy elements are also formed by reactions such as this.
Curve of inherent stability of nuclei has a maximum at Fe.
Heavy nuclei tend to undergo fission reactions. Ex. Radioactive series of U-238
Magic Numbers for Nuclear Stability No. of Protons: 2 8 20 28 50 82 114 No. of Neutrons: 2 8 20 28 50 82 126 184 Distribution of Naturally Occurring Stable Nuclides Combination Z even - N even Z even - N odd Z odd - N even Z odd - N odd
Number of Nuclides 163 55 50 4
Neutron-to-proton ratio and the stability of nuclides Possible heavy nuclides of high stability (long radioactive half-lives)
Naturally occurring and artificially made radioactive nuclides
Naturally occurring stable nuclides (ranging from H to Bi)
The cosmic abundances of some of the elements
Geochemical Classification of Elements
Siderophiles (iron-loving) - concentrate in the metallic core Litophiles (rock-loving) - abundant in crust, oxides and halides Chalcophiles - also found in crust, combine with S, Se and As Atmophiles - present as gases
1.8 x 1010 years ago ~0 V αT
where:
universe after 1 s
Few minutes later, after T dropped to 109 K The limiting reaction; the reverse reaction is also fast The interplay of the rates gives an atomic ratio of H/He = 10/1 Sun
Within 11.3 min, half the matter of the universe consisted of protons; the temperature was about 5 x 108 K. In the first 30 to 60 min, 2H, 3He, 4He, and 5He were formed. These nuclei were formed in the process called hydrogen burning.
In stars, with T at 107 to 108 K, production of heavier nuclei occurred. Among known reactions that take place under such conditions are called helium burning.
In more massive stars (T at 6 x 108 K or higher), the C-N cycle is possible:
Heavier elements were formed as shown:
At still higher temperatures, further reactions take place:
Formation of elements of higher atomic number takes place by addition of neutrons to a nucleus followed by electron emission decay. 56 26
!
1 0
69 26
69 27
0 #1
Fe + 13 n" Fe" Co+ e
In environments of low neutron density, the addition of neutron is very slow, one neutron at a time; in high neutron density, 10 to 15 neutrons may be added in a very short time. The very heavy elements are also formed by reactions such as this.
Curve of inherent stability of nuclei has a maximum at Fe.
Heavy nuclei tend to undergo fission reactions. Ex. Radioactive series of U-238
Magic Numbers for Nuclear Stability No. of Protons: 2 8 20 28 50 82 114 No. of Neutrons: 2 8 20 28 50 82 126 184 Distribution of Naturally Occurring Stable Nuclides Combination Z even - N even Z even - N odd Z odd - N even Z odd - N odd
Number of Nuclides 163 55 50 4
Neutron-to-proton ratio and the stability of nuclides Possible heavy nuclides of high stability (long radioactive half-lives)
Naturally occurring and artificially made radioactive nuclides
Naturally occurring stable nuclides (ranging from H to Bi)
The cosmic abundances of some of the elements
Geochemical Classification of Elements
Siderophiles (iron-loving) - concentrate in the metallic core Litophiles (rock-loving) - abundant in crust, oxides and halides Chalcophiles - also found in crust, combine with S, Se and As Atmophiles - present as gases
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