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Orbital diagrams represent the arrangement of electrons in orbitals. The aufbau principle: The atom is “built up” by progressively adding electrons. Electrons ...
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Section 3.
The Periodic Table is like a MAP that describes the arrangement of electrons within their orbitals.
1s
e.g., Hydrogen (Z=1) 1s
e.g., Helium (Z=2)
Within a principal energy level, s < p < d < f
Example: 3s fills before 3p
But… the (n+1) s orbitals always fill before the n d orbitals.
Example: 5s fills before 4d
Practice!
Draw an orbital diagram for beryllium (Z=4)
1s
nitrogen 14.
1s 2s 2p
oxygen 16.
1s 2s 2p
Orbital diagrams for ions
1s 2s 2p
Example: Oxide ion, O 2-
Before beginning, ask yourself: a) How many e -^ in a neutral oxygen atom? b) How many e -^ do I add/remove? c) What’s the new total number of e -?
Draw orbital diagrams for:
a) Sulfur (Z=16)
b) Iron (Z=26)
c) Aluminum (Z=13)
d) Nitride ion (Z=7)
Tip: Use lines instead of boxes to represent the orbitals.
4s 3d
Chromium:
Possible explanation: Filled and half-filled sub-shells have lower energy than unfilled ones more stable
Learning Checkpoint
An electron configuration is a shorthand notation that provides the same information as the orbital diagram.
boron 10.
Guidelines for writing electron configurations
Write electron configurations for:
a) Sulfur (Z=16)
b) Iron (Z=26)
c) Aluminum (Z=13)
d) Gold (Z=79)
For simplicity, electron configurations can be abbreviated :
Gold: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 6 6s 2 4f^14 5d 9
Nearest preceding noble gas
All the “extra” electrons
Elements in a group:
Why do atoms form ions?
All of these ions are ISOELECTRONIC with Neon.
They have the same electron configuration as Ne.
Pb: [Xe] 6s 2 4f 14 5d^10 6p^2
Pb4+^ : [Xe] 6s 0 4f 14 5d^10 6p^0
Lose 4e -
Pb2+^ : [Xe] 6s 2 4f 14 5d^10 6p^0
Lose 2e -
MO ORBITALS MO PROBLEMS
1s 2 2s 2 2p 6