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					         Electron Configuration

 More complex than simple concentric circles.
Orbit vs. orbital??
-orbit
     the path an electron takes (Bohr)
-orbital
     a region around the nucleus
     where an electron with a given
     energy is likely to be found
Orbitals and energy


-each principle energy level is divided
into one or more sublevels
  n=1 has one sublevel

         n=2 has two sublevels

             n=3 has three sublevels
         Orbital Representations

 Four basic orbital shapesThe s orbitals are
  spherical:




        1s          2s             3s
            p Orbitals: “peanut”
 Have two lobes lying along the x, y, or z axis.

 Different orientations labelled px, py, and pz.
Sodium Diagram
        d Orbitals: “double p”
Have complicated shapes, but the electron
density at the nucleus is always zero.
                  f Orbitals

 orbital shape highly varied
 high energy electrons
 How do energy levels,
sublevels, and orbitals fit
       together?
 Orbitals and energy

-principle energy levels proposed by
Bohr (n)
                               n=2
  n=1



                              n=3
Orbitals and energy (cont’d)

- there may be
only one of each                          s 1


                      Increasing energy
type of sublevel at
each energy level                         p 3

- each sublevel                           d 5
consists of one or
                                          f 7
more orbitals
 Orbitals and energy (cont’d)

-sublevels are written with the quantum
number and the type of orbitals

        1s              2p
         energy level   type of orbital
   1 st   principle energy level (n=1)

-since n=1, there is only one sublevel
                    1s
-the s sublevel only consists of one
orbital
-there is only 1 orbital in this
energy level
 2 nd   principle energy level (n=2)
-since n=2, there are two sublevels
               2s        2p
-there is one s orbital in the 2s sublevel
and three p orbitals in the 2p sublevel
-4 total orbitals in this energy level
  3 rd   principle energy level (n=3)

-since n=3, there are three sublevels
               3s   3p      3d
-there is 1 s orbital, 3 p orbitals,
     and 5 d orbitals
-9 total orbitals in this
      energy level
4 th   principle energy level (n=4)

How many sublevels?      4

Name the sublevels. 4s       4p 4d 4f

How many total orbitals? 16
Orbitals and energy (cont’d)

How does a 1s orbital differ from a 2s
              orbital?
How does a 2p orbital differ from a 3p
              orbital?
  SIZE & ENERGY
 Electron spin

-electrons behave as though they were
spinning on their own axis, creating a
magnetic field
-2 “types” of spin
          clockwise
          counterclockwise
 Electron spin (cont’d)

-if 2 electrons have opposite spins, they
cancel each other out
-if 2 electrons have parallel spins, there
is a net effect on the magnetic field
-each orbital can hold a maximum of 2
electrons
 Electron spin (cont’d)

sublevel   # of orbitals   max. # e-
   s             1            2
  p              3            6
  d              5            10
  f              7            14
  Remember Bohr’s atom                   (2n 2)?

Level (n)   sublevels        orbitals   max. # e-
  1         1 (s)               1        n=22
   n=1
  2         2 (s, p)            4             8
  3         3 (s, p, d)         9             18
  4         4 (s, p, d, f)      16            32
                                        n=3
 Writing electron configurations

An electron configuration shows the
distribution of electrons among orbitals
in an atom (location, energy).
         Why is it important?
-the behavior of atoms is determined by
the outer electrons (bonding)
 Electron configuration (cont’d)

When writing electron configurations,
you must obey three rules:
    1. The Aufbau Principle
    2. The Pauli Exclusion Principle
    3. Hund’s Rule
The Aufbau Principle

-electrons are added one at a time to
the lowest energy levels until all
electrons of the atom have been
accounted for
Aufbau Principle (cont’d)

      1s
      2s   2p
      3s   3p   3d
      4s   4p   4d   4f
      5s   5p   5d   5f
      6s   6p   6d   6f
      7s   7p   7d   7f
The Pauli Exclusion Principle

-an orbital can hold a maximum of 2
electrons
-the e- must have opposite spins
-termed “paired” and “unpaired”
 Hund’s Rule

-electrons occupy equal energy orbitals
so that a maximum number of unpaired
electrons results
-in a sublevel, you place one e- in each
orbital first, the go back and pair them
up
Example
lithium
3e- 2e- 1e-

               orbital diagram
1s        2s

1s22s1         e- configuration
 Example
oxygen
8e- 7e- 6e- 5e- 4e- 3e- 2e- 1e-


1s     2s         2p

 1s22s22p4
Practice Problem
Write the orbital diagram and electron
      configuration for sodium.


1s    2s         2p            3s
1s22s22p63s1
 Practice Problem

 Write the orbital diagram and electron
        configuration for nickel.

1s 2s    2p   3s    3p    4s     3d


 1s22s22p63s23p64s23d8
     Valence Electrons in Yellow
H       1s1
He      1s2         full   Noble gas
Li      1s2,2s1
Be      1s2,2s2
B       1s2,2s2p1
C       1s2,2s2p2
N       1s2,2s2p3
O       1s2,2s2p4
F       1s2,2s2p5
Ne      1s2,2s2p6   full   Noble gas
     Electron Configurations and the
             Periodic Table
Write electron configurations for:

   13 Al: 1s2 2s2 2p6 3s2 3p1
                 [Ne] 3s2 3p1

  26 Fe: [Ar] 4s2 3d6         [Ar]
                                     4s   3d
  50 Sn: [Kr] 5s2 4d10 5p2

82 Pb+2: [Xe] 6s2 4f14 5d10

   92U: [Rn] 7s2 6d1 5f3

				
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posted:12/4/2011
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