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									         Lecture 26: Nuclear Bombs &
              Organic Chemistry
                           1) How to make nuclear bombs
                        2) Introduction to organic chemistry
                             3) Hydrocarbons: Alkanes
                            4) Nomenclature of Alkanes




Chemistry 2C Lecture 25: June 2nd, 2010                        1
                                          Nuclear Bombs
                                               We has earlier separated nuclear
                                                   energy into either fusion or
                                                  fission depending on whether
                                                we are discussing heavy or light
                                                            elements.


                                               Nuclear Bombs can also be based
                                                        on either process:

                                                1) Fission (atomic bombs, atom
                                                      bombs, or A-bombs ) or

                                                2) Fusion (hydrogen bombs, H-
                                                  bombs, thermonuclear bombs,
                                                        and fusion bombs)
Chemistry 2C Lecture 25: June 2nd, 2010                                            2
               Nuclear Bombs and Critical Mass
                                          The critical mass of fissile material is the amount
                                              needed for a sustained nuclear chain reaction.
                                              Surrounding fissionable material by a neutron
                                                reflector reduces the needed mass, while
                                            attenuating fission with an absorber will require
                                                                   more.




                                                   Again, nuclear power requires
                                                    controlling the chain reaction
                                                     (sub-critical), whilst nuclear
                                                   bombs require letting the beast
                                                              go critical!



Chemistry 2C Lecture 25: June 2nd, 2010                                                         3
                                 Fission based bombs
      The quickest way to make an uncontrolled critical nuclear chain reaction is to
         rapidly increase the mass of fissionable material beyond the critical mass.




                                             This can be attained via conventional
                                                  explosives that combine two or
                                                    more sub-critical pieces of
                                                 fissional material together. This
                                                  larger mass of material is then
                                                    capable of initiating a chain
                                                   reaction and then the nuclear
                                                         explosion starts!




Chemistry 2C Lecture 25: June 2nd, 2010                                                4
                                  Fusion based bombs
       Fusion bombs are harder to developed as you would expect, since a massive
              barrier must be overcome before effective fusion can take place!




                                          A small fission bomb is used to initiate
                                                   the fusion reaction in the
                                                secondary stage of the bomb.




                                             This dry fuel, when bombarded by
                                                  neutrons, produces tritium, a
                                                heavy isotope of hydrogen which
                                               can undergo nuclear fusion, along
                                                 with the deuterium present in
                                                          the mixture.




Chemistry 2C Lecture 25: June 2nd, 2010                                              5
                      Two other types of bombs…
                 Enhanced radiation bombs (e.g. neutron bombs):
These are bombs that are designed to not destroy targets with an uncontrolled
     reaction, but to generate an enhanced radiation field (for eg. Neutrons)
       that will kill people, but leave the buildings standing. A neutron bomb
   requires considerable amounts of tritium, which has a relatively short half-
                                          life.




                           Salted bombs (cobalt bombs):
     A salted bomb is a nuclear weapon constructed like fission-fusion-fission
       weapons, but instead of a fissionable jacket around the secondary stage
       fusion fuel, a blanket of a specially chosen isotope of a non-fissionable
        element. This blanket captures the escaping neutrons to maximize the
      radiation hazard from the weapon. The primary purpose of this weapon is
        to create extreme radioactive fallout to deny a region to an advancing
                      army, a sort of wind-deployed mine-field.


Chemistry 2C Lecture 25: June 2nd, 2010                                            6
                                          Organic Chemistry




Chemistry 2C Lecture 25: June 2nd, 2010                       7
                      What is Organic Chemistry?
           It is the scientific study of the structure, properties, composition,
              reactions, and preparation (by synthesis or by other means) of
           chemical compounds of carbon and hydrogen, which may contain any
            number of other elements, such as nitrogen, oxygen, halogens, and
                             more rarely phosphorus or sulphur




                               7 million Organic Compounds
                               1.5 million Inorganic Compounds



            Knowledge of organic chemistry is important to understand:
            Animal and plant matter, Foods, Pharmaceuticals, Cosmetics,
                Fertilizers, Plastics, Petrochemicals, Clothing, Life

Chemistry 2C Lecture 25: June 2nd, 2010                                            8
Organic chemistry and the periodic Table
                   These are the principle elements involved in o-chem




Chemistry 2C Lecture 25: June 2nd, 2010                                  9
                   Carbon (the basis for o-chem)

                               Why is it the element of life on earth?


                                            * Has Four Bonding Electrons


                                          * Unique Strong Covalent Bonds


                          * Can form Strong Single, Double and Triple Bonds


                                          Average Bond Energies (KJ mol-1)
                 C-C         607           Si-Si   230      C-H     416      Si-H   323
                 C-N         754           Si-N    470      C-O     336      Si-O   368


                          * Can form chains or networks of carbon polymers


Chemistry 2C Lecture 25: June 2nd, 2010                                                   10
                                 The Simplest Organic molecule

                             Carbon has 4 valence electrons

                                 H              H
                        H C H             H C H              Ne
                                 H              H           Neon
                          methane
                                            H       C

                                          Stable Octet required

                 Covalent Bonding – Atoms Share Electrons
Chemistry 2C Lecture 25: June 2nd, 2010                            11
     Orbital overlaps involved in s bonds of
                    methane




Chemistry 2C Lecture 25: June 2nd, 2010        12
                                          Alkanes

              • Hydrocarbon chains where all the bonds
                between carbons are SINGLE bonds
              • Name uses the ending –ane
              • Examples: Methane, Propane, Butane, Octane,
                2-methylpentane




Chemistry 2C Lecture 25: June 2nd, 2010                       13
                                    Alkanes (CnH2n+2)
   consist of only carbon and hydrogen bonded by single covalent bonds single
        H             H H                   H H H         H H H H          H H H H H
      H C H         H C C H               H C C C H     H C C C C H      H C C C C C H
        H             H H                   H H H         H H H H          H H H H H

      methane           ethane             propane              butane      pentane
      CH3           CH3CH3                CH3CH2CH3      CH3CH2CH2CH3      CH3CH2CH2CH2CH3


                   Skeletal structure of only carbon atoms

                                                      propane

                                                        butane


                                                          pentane


                             C1 – C4 n-alkanes are all gases
                         Methane main component of natural gas
                  Propane and butane often stored as compressed gases
Chemistry 2C Lecture 25: June 2nd, 2010                                                      14
                Physical Properties of Alkanes

                 Non-polar molecules, which are less dense than water.
                 Alkanes are immiscible with water making two layers.

 Van-der Waals or dipole-dipole attractive forces, and not H-bonding (as in
           polar molecules) are the main intermolecular forces

  Alkanes show regular increases in boiling and melting points as molecular
               weight increases down the homologous series

  These weak intermolecular forces operate over small distances, arising
 because the electron distribution within molecules at any given instance is
  not uniform. Resulting in tiny electrical attractions between molecules.

    These temporary dipoles hold alkanes as liquids or solids, and must be
         overcome in order to vaporize a liquid or melt a solid (wax)

Chemistry 2C Lecture 25: June 2nd, 2010                                       15
     IUPAC Rules for Alkane Nomenclature
      1. Find and name the longest continuous carbon chain. This is
        called the parent chain. (Examples: methane, propane, etc.)

      2. Number the chain consecutively, starting at the end nearest an
        attached group (substituent).

      3. Identify and name groups attached to this chain. (Examples:
        methyl-, bromo-, etc.)

      4. Designate the location of each substituent group with the
        number of the carbon parent chain on which the group is
        attached. Place a dash between numbers and letters. (Example:
        3-chloropentane)

      5. Assemble the name, listing groups in alphabetical order.
           The prefixes di, tri, tetra etc., used to designate several
        groups of the same kind, are not considered when alphabetizing.
        Place a comma between multiple numbers. (Example: 2,3-
        dichloropropane)
Chemistry 2C Lecture 25: June 2nd, 2010                                   16
                Step 1. Find the parent chain.

      • Where is the longest continuous chain
        of carbons?




Chemistry 2C Lecture 25: June 2nd, 2010          17
                      Prefixes for # of Carbons

          1          Meth-                6    Hex-

          2          Eth-                 7    Hept-

          3          Prop-                8    Oct-

          4          But-                 9    Non-

          5          Pent-                10   Dec-


Chemistry 2C Lecture 25: June 2nd, 2010                18
                                          Endings
      • Alkanes (all C-C single bonded parent chain) end in –
        ane
         – Methane CH4
         – Ethane C2H6
         – Propane C3H8
      • Attached carbon groups (substituents) end in –yl
         – Methyl CH3 -
         – Ethyl CH3CH2-
         – Propyl CH3CH2CH2 –



                                                    3-ethylpentane


Chemistry 2C Lecture 25: June 2nd, 2010                              19
           Step 2. Number the parent chain.
      • Number the parent chain so that the attached groups
        are on the lowest numbers

                                          Methyl is on carbon #2 of the parent chain
                                          Methyl is on carbon #4 of the parent chain


                     1          2         3      4      5         GREEN is the right
                      5          4         3      2      1
                                                                   way for this one!

              1 8         27
                          3 6              7 2            1   2      3     4     5          6
                  8 1
                                                          7   6      5     4     3        72
                          4 5     5 4      6 3                                           1

            Groups on 4, 6, and 7                                    Groups on 2 and 5
            Groups on 2, 3, and 5                                    Groups on 3 and 6
Chemistry 2C Lecture 25: June 2nd, 2010                                                         20
         Step 3. Name the attached groups.

                       • Carbon (alkyl) groups
                             – Methyl CH3 -
                             – Ethyl CH3CH2-
                             – Propyl CH3CH2CH2 –
                       • Halogens
                             –   Fluoro (F-)
                             –   Chloro (Cl-)
                             –   Bromo (Br-)
                             –   Iodo (I-)


Chemistry 2C Lecture 25: June 2nd, 2010             21
         Step 4. Designate where the group
          is attached to the parent chain.

      • Use the numbers of the parent chain from step 2 to
        designate the location of the attached groups to the
        parent chain.


                                                  2-methyl




                                          1   2    3     4   5




Chemistry 2C Lecture 25: June 2nd, 2010                          22
            Step 5. Alphabetize the groups,
           combine like groups, and assemble.

   • The prefixes di, tri, tetra
     etc., used to designate several
     groups of the same kind
   • Prefixes are not considered
     when alphabetizing (Example:
     dimethyl = m for
     alphabetizing)                       1,1,1-trichloro-1-   1,1-dichloro-1,1-
   • Parent chain goes LAST               fluoromethane        difluoromethane




Chemistry 2C Lecture 25: June 2nd, 2010                                        23
                     Draw Some Simple Alkanes

      • 2-methylpentane

      • 3-ethylhexane

      • 2,2-dimethylbutane

      • 2-methyl, 3-ethylbutane


Chemistry 2C Lecture 25: June 2nd, 2010         24

								
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