#### Transcript Ch. 4/5 : Atomic Structure

Atomic Structure
Electron Configurations
Electron Configurations
• the arrangement of electrons in an atom
• each element has a unique electron
configuration
• electrons fill the lowest energy levels
first
• ground state electron configurationlowest energy arrangement of electrons
Rules for Arrangements
• Aufbau Principle- an
electron occupies the
lowest-energy orbital
• Beginning in the 3rd
energy level, the
energies of the
sublevels begin to
overlap
Rules for Arrangements
• Pauli Exclusion Principle- no two
electrons in the same atom can
occupy the same place at the same
time
• Hund’s Rule- orbitals of a sublevel
are each occupied by one electron
before any orbital is occupied by a
second and 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
• How many e- in the atom?
• What sublevel (s,p,d,f) is the element
in?
• 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
1s2 2s2 2p6 3s1
2p
3s
Calcium
• number of electrons: 20
• last electron is in sublevel: 4s
1s
2s
3p
2p
4s
1s2 2s2 2p6 3s2 3p6 4s2
3s
Argon
• number of electrons: 18
• last electron is in sublevel: 3p
1s
2s
2p
1s2 2s2 2p6 3s2 3p6
3s
3p
Bromine
• number of electrons: 35
• last electron is in sublevel: 4p
1s
4s
2s
2p
3d
3s
3p
4p
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5
Noble Gas Notation
• short hand for larger atoms
• configuration for the last noble gas is
abbreviated by the noble gas’s symbol in
brackets