Electron
Configuration
Ch. 4 - Electrons in
Atoms
December 11
• You will learn three ways to describe how
electrons are configured around an atom
• In this section of notes:
– Orbital Notation
– Longhand
Orbitals Overlap Each Other
A few definitions
Electron Configuration:
Arrangement of electrons in the atom
Core
Core
Electrons:
Electrons:Inner
Inner
electrons
electrons
Valence
Valence
Electrons:
Electrons:Outer
Outer
shell
shell
Arrows Point to VALENCE electrons
General Rules
• Pauli Exclusion Principle
– Each orbital can hold TWO electrons with
opposite spins.
– Up and down arrows are used to show opposite
spins.
General Rules
• Aufbau Principle
– Electrons fill the
lowest energy
orbitals first.
– “Lazy Tenant
Rule”
What order do they fill?
ALWAYS fill in the same order
1s
2s
2p
3s
3p
4s
3d
4p
5s
4d
ETC.
Periodic Patterns
OR, read the periodic table from left to right (like a page) to find the order
s
p
1
2
3
4
5
6
7
d
f
6
7
© 1998 by Harcourt Brace & Company
General Rules
• Hund’s Rule
– Within a sublevel, place one e- per orbital before
pairing them.
– “Empty Bus Seat Rule”
WRONG
WRONG
RIGHT
RIGHT
Orbital Diagram: Description
• Electrons are represented by arrows
• Orbitals represented by boxes or lines
• Tips:
–
–
–
–
s always has 1 line (can hold 2 e-)
p always has 3 lines (can hold 6 e-)
d always has 5 lines (can hold 10 e-)
f always has 7 lines (can hold 14 e-)
Oxygen
• 8 electrons, found on 2p
• ____
1s
____
2s
____ ____ ____
2p
• 8 electrons = 8 arrows
Aluminum
• 13 electrons, found on 3p
•
1s
2s
2p
• 13 electrons = 13 arrows
3s
3p
Germanium, Ge
• 32 electrons, found on 4p
•
1s
4s
2s
2p
3d
• 32 electrons = 32 arrows
3s
3p
4p
Longhand Configuration
• States the energy level, sublevel of each
orbital and how many electrons are in each
orbital
Energy level
1
2
Sublevel
s
Number of electrons
in orbital
Oxygen
• 8 electrons, found on 2p
• ____
____
1s
2s
• 1s22s22p4
____ ____ ____
2p
Aluminum
• 13 electrons, found on 3p
•
1s
2s
• 1s22s22p63s23p1
2p
3s
3p
Germanium, Ge
• 32 electrons, found on 4p
•
1s
4s
2s
2p
3d
• 1s22s22p63s23p64s23d104p2
3s
3p
4p
Practice (p. 10), #1
• Phosphorus, P
• Sodium, Na
Practice (p. 10), #2
• Cl
• 1s22s22p63s23p5
• Te
• 1s22s22p63s23p64s23d104p65s24d105p4