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```Electron Configuration
Topic #8
September 2012
How was the Atomic Model
developed?
 The first modern atomic theory, proposed by
Dalton, portrayed the atom as a solid indivisible
mass.
 After the discovery of the electron by J. J.
Thomson, the atomic model was revised to
include them. J. J. Thomson’s model is referred
to as the “plum-pudding” model.
 Rutherford pictured the atom as a dense
nucleus surrounded by electrons.
 In the Bohr model, the electrons move in circular
paths.
 The quantum mechanical model is the modern
description of the electrons in atoms. This
model estimates the probability of finding an
electron within a certain volume of space
surrounding the nucleus.
Schrodinger
What are Atomic Orbitals?
Atomic orbitals are
regions around the nucleus
within which the electrons
have the highest
probability of being found.
Energy levels are regions
in space around the
nucleus where an electron
is likely to be moving.
Before we start……….
ONLY one paper and
pencil/pen for you and your
shoulder partner
Using Rally Robin…….
Discuss what Mr. Tapia is doing on the
board!!
Try to relate what he is writing on the
board and the handout you received when
you entered the room
1st partner has 30 seconds to tell the other
partner his/her ideas
2nd partner has now 30 seconds to share
his/her ideas with the 1st partner
General Patterns of Filling Orbitals
Let’s Practice Using Rally
Coach!
Write the electron configuration for the
following atoms:
1.C
2. S
3. K
4. Ar
1s2 2s2 2p2
1s2 2s2 2p6 3s2 3p4
1s2 2s2 2p6 3s2 3p6 4s1
1s2 2s2 2p6 3s2 3p6
Let’s Practice Using Rally Coach!
Write the electron configuration for the
following atoms:
Rubidium
Helium
Phosphorus
Iron
Arsenic
1s22s22p63s23p64s23d104p65s1
1s2
1s22s22p63s23p3
1s22s22p63s23p64s23d6
1s22s22p63s23p64s23d104p3
Let’s Practice!
Which atoms are these?
1. 1s2 2s2 2p4
2. 1s2 2s2 2p6 3s2 3p2
3. 1s2 2s2 2p6 3s2 3p6 4s2
4. 1s2 2s2 2p6 3s2 3p5
1.O
2.Si
3.Ca
4.Cl
THE ELECTRON
CONFIGURATION
E.Q.: HOW IS THE ARRANGEMENT OF ELECTRONS
EXPRESSED THROUGH ELECTRON CONFIGURATIONS
AND LEWIS DOT STRUCTURES?
How are Electrons Arranged in an Atom?
 The ways in which electrons are
arranged around the nuclei of atoms are
called electron configurations.
 It is also the most stable arrangement of
electrons around the nucleus of an atom
(ground state of electrons).
Noble Gas Notation for Electron
Configuration
You do not have to repeat yourself over and over
1. Oxygen  1s22s22p4
[He] 2s2 2p4
2. Silicon  1s22s22p63s23p2
[Ne] 3s2 3p2
3. Calcium  1s22s22p63s23p64s2
[Ar] 4s2
22s22p63s23p5
1s
4. Chlorine 
[Ne] 3s2 3p5
How are Electron Configurations for
Atoms written?
Rules that govern Electron Configuration:
1. Aufbau principle
Electrons enter orbitals of lowest energy first.
2. Hund’s rule
When electrons occupy orbitals of equal
energy, one electron enters each orbital until
all the orbitals contain one electron with
parallel spin.
3. Pauli exclusion principle
An atomic orbital may describe at most two
electrons with opposite spins.
General Patterns of Filling Orbitals
Bell Ringer
Give both the expanded and noble
gas notation for the elements…
1.
2.
3.
4.
5.
[He] 2s22p3
Nitrogen 1s22s22p3
Argon 1s22s22p63s23p6 [Ne] 3s23p6
Titanium 1s22s22p63s23p64s23d2 [Ar] 4s23d2
Selenium1s22s22p63s23p64s23d104p4 [Ar]4s23d104p
Strontium 1s22s22p63s23p64s23d104p65s2
[Kr]5s2
References
Wilbraham, Antony C., Dennis C. Staley,
Michael S. Matta, and Edward L.
Waterman. Chemistry. New Jersey:
Prentice Hall, 2002.
Summary of Principal Energy Levels,
Sublevels, and Orbitals
Principal
Energy Level
Number of
Sublevels
Type of Sublevel
n=1
1
1s (1 orbital)
n=2
2
2s (1 orbital) 2p (3 orbitals)
n=3
3
3s (1 orbital) 3p (3 orbitals) 3d (5 orbitals)
n=4
4
4s (1 orbital) 4p (3 orbitals)
4d (5 orbitals) 4f (7 orbitals)
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