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Ch. 4 Arrangement of Electrons in Atoms

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					Ch. 4 Arrangement of
 Electrons in Atoms
  4.3 Electron Configurations
      Electron Configurations
• the arrangement of electrons in an atom
• each type of atom has a unique electron
  configuration
• electrons tend to assume positions that
  create the lowest possible energy for atom
• ground state electron configuration- lowest
  energy arrangement of electrons
         Rules for Arrangements
• Aufbau Principle- an
  electron occupies the
  lowest-energy orbital
  that can receive it

• Beginning in the 3rd
  energy level, the
  energies of the sublevels
  in different energy levels
  begin to overlap
      Rules for Arrangements
• Pauli Exclusion Principle- no two electrons
  in the same atom can have the same set
  of 4 quantum numbers
• Hund’s Rule- orbitals of equal energy are
  each occupied by one electron each
  before any orbital is occupied by a second
• all unpaired electrons must have the same
  spin
Rules for Arrangements
   Writing Configurations

• Orbital Notation:
  – an orbital is written as a line
  – each orbital has a name written below it
  – electrons are drawn as arrows (up and down)
• Electron Configuration Notation
  – number of electrons in sublevel is added as a
    superscript
Order for Filling Sublevels
        Writing Configurations
• Start by finding the number of electrons in the
  atom
• Identify the sublevel that the last electron added
  is in by looking at the location in periodic table
• Draw out lines for each orbital beginning with 1s
  and ending with the sublevel identified
• Add arrows individually to the orbitals until all
  electrons have been drawn
                        Silicon
   • number of electrons: 14
   • last electron is in sublevel: 3p


 1s     2s             2p           3s   3p




Valence Electrons- the electrons in the outermost
    energy level
                    Chlorine
• number of electrons: 17
• last electron is in sublevel: 3p


     1s     2s          2p           3s   3p
                       Sodium
• number of electrons: 11
• last electron is in sublevel: 3s



1s        2s           2p            3s



     1s2 2s2 2p6 3s1
                      Calcium
• number of electrons: 20
• last electron is in sublevel: 4s



1s        2s             2p          3s


        3p          4s


     1s2 2s2 2p6 3s2 3p6 4s2
                        Bromine
 • number of electrons: 35
 • last electron is in sublevel: 4p



1s      2s        2p          3s             3p


4s                 3d                   4p


     1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5
                       Argon
 • number of electrons: 18
 • last electron is in sublevel: 3p



1s      2s        2p          3s      3p



     1s2 2s2 2p6 3s2 3p6
         Noble Gas Notation
• short hand for larger atoms
• configuration for the last noble gas is
  abbreviated by the noble gas’s symbol in
  brackets
             Homework
• Review 98-104, Study 105-116 do 1-5
  pg116

				
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