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Shape_of_orbitals

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					            Shape of orbitals




s-orbital      p-orbitals
Electrons can only occupy so-called atomic orbitals with well defined
energy levels corresponding to the principal quantum number, n. The
lowest level will have n = 1, the next n = 2, and so on.

Electrons must always enter the first available orbital of lowest energy.
The first element, hydrogen, only has one electron, and so this electron
must enter the 1s orbital.

The electronic configuration of hydrogen in the ground state must therefore
be: H 1s1.
Boron 1s2 2s2 2p1
Atomic number 5




Carbon 1s2 2s2 2p2
Atomic number 6




According to Hund’s rule, fill a set of similar energy orbitals with as many
unpaired electrons as possible (as in the p or d orbitals).
    The successive ionization energies of sodium [Ar] 3s1
                                       Ionization
              Electron removed                                  orbital
                                       energy/KJmol-1
              1st                      496                      3s1
              2nd                      4565
              3rd                      691
              4th                      9544
              5th                      13 352                    2p6, 2p2
              6th                      16 611
              7th                      20 115
              8th                      25 491
              9th                      28 934
              10th                     141 367                  1s2
              11th                     159 079                  1s1

•    One electron furthest away from nucleus easiest to remove (3S1)
•    Eight nearer to nucleus, harder to remove (2p6, 2p2)
•    Two very close to the nucleus and most difficult to remove (1s2)
•    Proves numbers of electrons in each shell is 2,8,1
 First ionisation energies (IE) of elements in
             periods 2 to 4/KJmol-1
IEs increase across period (nuclear charge increasing,
shielding the same)



  Li,     Be,      B,      C,       N,      O,      F,     Ne,
  520     900      801     1086     1402    1314    1681   2081

                                                                  IEs decrease
  Na,     Mg,      Al,     Si,      P,      S,      Cl,    Ar,    down a group
                                                                  (distance of outer
  495     735      580     780      1060    1005    1255   1527
                                                                  electrons from
                                                                  nucleus
                                                                  increasing)
  K,      Ca,      Ga,     Ge,      As,     Se,     Br,    Kr,
  419     590      579     762      947     941     1140   1351
     First ionisation energies (IE) of elements in
                 periods 2 to 4/KJmol-1
1.     Look at group II and group III: the first electron for Al is a 3P1 electron and is less
       tightly held than 3S electron as it is further away from nucleus
2.     Look at group V and group VI: a paired electron is easier to remove than an
       unpaired electron and the configuration for sulfur is 3P4, so it has a paired
       electron


          Li,      Be,      B,        C,       N,       O,       F,       Ne,
          520      900      801       1086     1402     1314     1681     2081


          Na,      Mg,      Al,       Si,      P,       S,       Cl,      Ar,
          495      735      580       780      1060     1005     1255     1527


          K,       Ca,      Ga,       Ge,      As,      Se,      Br,      Kr,
          419      590      579       762      947      941      1140     1351
         The Ionization Energies for elements in Period 3


 Element     I1    I2     I3      I4      I5      I6      I7     configuration


    Na       495   4560                                            [Ne]3S1


    Mg       735   1445   7730                                     [Ne]3S2


    Al       580   1815   2740   11600                           [Ne]3S23P1


    Si       780   1575   3220   4350    16100                   [Ne]3S23P2


     P      1060   1890   2905   4950    6270    21200           [Ne]3S23P3


     S      1005   2260   3375   4565    6950    8490    27000   [Ne]3S23P4


    Cl      1255   2295   3850   5160    6560    9360    11000   [Ne]3S23P5


    Ar      1527   2665   3945   5770    7230    8780    12000   [Ne]3S23P6


I1 = first ionization energy;  A(g)        A+(g) + e-
I2 = second ionization energy; A+(g)       A2+(g) + e-
I3 etc.

				
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posted:4/2/2013
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