Chemical Engineering Notes Class 333 Part 02

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Chemical Engineering Notes Class 333 Part 02 Powered By Docstoc
					               Class 2
    How Atoms combine with similar
         and dissimilar atoms
•   Periodic table
•   Electron configurations
•   Energies
•   Bond types
•   Bond types and properties.


                                     Fall 08
Columns represent groups of similar properties, Group 1A, alkali metals; 8, inert gases; 7B halides
Atomic Model


       Nucleus – Protons +ve charge
                 Neutrons no charge

       Orbitals – Electrons –ve charge

       Atoms – protons and electrons
               balance each other, so
               no net charge.

       Ions – Positive or negative
              charge imbalance
                        -
              Na+ or Cl
       Quantum mechanical model
       Replaced this one
              Electron States




Each Quantum Number Fills up first- 1, 2, 3,4,5,6 etc
Chlorine atom, z=17, 1s2,2s2,2p6,3s2,3p5, electrons = 2+2+6+2+5=17
               2
So 1S2,then 2S ,2p6, then 3S2,3P6,3D10,then 4S etc – there are some
Discrepancies though.
Note 4s before 3d




    Note 4s1 3d5



     Note 4s1 3d10
     Electron Filling of Orbitals
1s 2s 2p 3s 3p 3d 4s 4p 4d            Z=   46
1s 2s 2p 3s 3p 3d 4s 4p                    36
1s 2s 2p 3s 3p 3d 4s                       30
1s 2s 2p 3s 3p 4s                          20
1s 2s 2p 3s                                12
1s 2s 2p                                   10
1s 2s                                      4
1s                                         2
On Ionisation, 4s levels empties first.
             Filling of Shells
• Electrons shells like to be full, half full or
  empty.
• Full shells – inert status, for example
  helium
• Full or empty, between elements by ionic
  or covalent bonding.
• Metallic bonding – sharing of electrons.
           Periodic Table
• Rows – number of shells 1,2,3,4 etc
• Column – number of electrons in outer
  shell
• Columns have like properties as number
  of electrons in outer shell same.
• Atomic number – number of electrons and
  so protons in atom.
• Different number of electrons changes
  properties and produces elements
           Bonding Types
• Between like atoms – metallic or covalent
• Between different atoms – metallic, ionic
  or covalent.
• Primary – ionic, covalent and metallic.
            strong
• Secondary – hydrogen, van der Waals.
              weak.
                                        4s level just below 3d




Ionisation energies for the hydrogen atom
               Ionic Bonding




Na, z=11, # of electrons and protons, 1s2,2s2,2p6,3s1 : 2+2+6+1=11
Note 3s1, lose this electron, full orbitals then ; alkali metals
Cl, z=17, 1s2,2s2,2p6,3s2,3p5 : 2+2+6+2+5=17
Note 3p5, gain one electron, full 3p6 orbital, halide ions
Na+ ion due to loosing one electron, Cl- due to gaining an electron
Ionic bonding between elements with different electronegativities.
Elements on right of periodic table highly electronegative, and want to
Gain electrons, elements on left electropositive, lose an electron.
Directional so brittle type materials. Ordered structure, move one ion
Lose order.Crystalline structure from this bonding.
              Covalent Bonding




Hydrogen 1s1, Carbon 1s2,2s2,2p2, so if hydrogen can share one electron
And carbon can share four electrons, both elements will have full orbitals.
Four hydrogens share with one carbon in covalent bonds.
Molecule of methane gas formed – different elements or same can exhibit
Covalent bonds eg carbon.Elements with half full outer orbital.Can be crystalline
              Metallic Bonding

                                                      Ion cores protons
                                                      And neutrons




Electrons shared in a gas cloud as outer orbitals not filled. Lots of empty
energy states, such as 3d etc. Can be single element, eg gold, or mixtures
such as brass, or aluminum alloys. No directionality to bonds, so ductile
and conductive. Crystalline usually, but not ordered.
               Metallic Conductivity




Electrons in                                              Electrons out




     Metals are conductive as the electrons are not specific to an ion
     Applications – electrical wire, copper circuit boards, thermocouples.
          Bond Energy and Properties
                                                      State
                                                      25 C
                                                      Solid
                                                      Solid
Primary
                                                      Solids
Primary
                                                      Liquid
                                                      Solid
                                                      Solid
Primary                                               Solid

                                                      Gases
Secondary

Secondary


                Bond energy controls melting point.
        Secondary Bonding
• Hydrogen – needs presence of hydrogen,
             single electron effect,
             non crystalline normally

• Van Der Waals – dipole type bonding, due
  to slight charge imbalance with distance.
  Non crystalline normally.
Secondary Bonding



            Positive charge here as electron
            Favors carbon side
            Water good example of hydrogen bond
            Between hydrogen and oxygen covalent
            Between molecules, hydrogen bond.
              Homework
• How does calcium and flourine bond to
  each other?
• How does aluminum bond to other
  aluminum atoms and how does silicon
  bond to other silicon atoms?
• Why are metals conductive?

				
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