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5.3 – Electron Configurations
• OBJECTIVES: Students will be able to (SWBAT)
1. Draw orbital diagrams of the electron configuration of
atoms
2. Write electron configuration notations for atoms2. Write electron configuration notations for atoms
• 5 lecture Q’s
• 5-sentence summary (combine with 5.2 and
reading)
Notes: Electron Configurations
(5.3)
Ground State Electron Configuration
• Electrons in an atom will arrange themselves
to give the atom the lowest possible energy
(most stable) � ground state electron
configuration (arrangement)configuration (arrangement)
Ruling Principles of Electron Arrangement
• 3 major priniciples:
– Aufbau Principle – electrons fill lowest energy
levels first.
– Pauli Exclusion Principle – only 2 electrons can – Pauli Exclusion Principle – only 2 electrons can
occupy an orbital and must have opposite spins
(means they move in opposite directions)
– Hund’s Rule – electrons fill the orbitals of an
energy level with the same spin first then the
opposite spin.
Orbital Filling Sequence Diagram
• Diagram
– Lowest energy level on the bottom (1st, 2nd, 3rd
and so on)
• s sublevels first, then p, then d, then f• s sublevels first, then p, then d, then f
• Boxes represent an orbital
Electrons as Arrows on the Diagram
• Arrows (↑, ↓) represent electrons with
different spins
Orbital Filling Sequence Diagram
Energy Level Overlap
•d sublevels of a
level actually
come after the s
sublevel of the sublevel of the
next level
- For example,
3d will come
after 4s
Orbital Diagrams and Electron
Configuration Notation
• Filling sequence:
Pauli’s principle: each orbital can hold 2 e-
s �1 orbital � can hold 2 e-s �1 orbital � can hold 2 e-
p � 3 orbitals � total of 6 e-
d � 5 orbitals � total of 10 e-
f � 7 orbitals � total of 14 e-
Sublevel and Orbital Order
1s2
1s22s22p61s 2s 2p
How to Write Noble Gas Configuration
1) Use the LAST column of elements only (the
noble gases) in the brackets [ ]
2) Continue with the next row (starting always
with s orbitals, then d (if needed), then pwith s orbitals, then d (if needed), then p
3) Always use the closest previous noble gas for
the short-cut
Electron Configuration (e- config) Notation
• e- config notation is another way to show electron
arrangement in an atom
• Use orbital diagrams to help write e- config notations
• Write the number of electrons in each orbital as
superscriptssuperscripts
• Long-hand notation: ALL orbitals are written out with
number of electrons
• If all superscripts in the notation are added, it should
add up to the total number of electrons in the atom
2+2+4 = 8 electrons
How to Write Noble Gas Configuration –
Short-hand Notation
• Uses noble gas e-config notation to abbreviate
longer notations
1) Noble gas element is written in brackets [ ]
2) Use the noble gas (the ones in the last column) 2) Use the noble gas (the ones in the last column)
immediately before the element for which you’re
writing the notation
3) Write the remaining orbitals after the noble gas
until you reach the appropriate number of
electrons
1s2
1s22s22p61s 2s 2p
Examples
• Kr: 1s22s22p63s23p64s23d104p6
• Sr: 1s22s22p63s23p64s23d104p6 5s2[Kr]
Practice
• In your blank orbital diagram worksheet,
complete one diagram for selenium (Se).
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