12.1: ELECTRON CONFIGURATIONS
THE QUANTUM MECHANICAL MODEL OF THE ATOM
(This is the current model of the atom)
Major contributors = de Broglie, Shrodinger & Heisenberg (…and many others)
- Employs very complicated mathematics to describe the _________, __________ and __________ of an electron around
the nucleus.
*What are some of the ways in which the Bohr Model has been modified?
1) _____________________________________:
 Louis de Broglie hypothesized that an electron could behave like a _________
(1923). This hypothesis received ______________ ____________ in 1927.
*2) ________________________:
 The nature of spectra produced by multi-electron atoms suggested that there were
smaller energy differences within energy levels. It was hypothesized that there were
________________ within each energy level.
*3) __________________________________:
 Via mathematics, the part of Bohr’s theory outlining the fixed orbits of
electrons around the nucleus was proven flawed.
To describe the location of an electron, scientist used _____________. An
Austrian physicist, name ______________ ______________, used a type of
equation called a _______ equation to define the _______________ of finding
an atom’s electrons at a particular point within the atom at a particular time.
There are many solutions to this wave equation, and each solution represents a
particular wave function. Chemists call the solutions to these wave functions
____________.
 An orbital is a region of space around the nucleus of an atom where there is a high probability of locating an
electron. Each orbital has its own associated energy, and each represents information about where, inside the atom, the
electrons would spend most of their time.
ORBITS VS. ORBITALS
ORBITS
ORBITALS
EXTENSION: QUANTUM NUMBERS
1. Principle Quantum Number, n
- identifies __________ possessed by electron in any orbital (i.e. energy level)
- n = 1 to  , where n = 1, 2, 3 …, 
- For every n, there are n types of orbitals and n2 actual orbitals.
Example:
Principal
# of Different
# of Orbitals in
Quantum
Types of Orbitals
Energy Level
Number
(same as “n”)
(n2)
(Energy Level)
Total Number of
Electrons in
Energy Level
(2n2)
2. Secondary Quantum Number, l
- identifies the “shape” of the orbital
*Ex.
l
s-orbitals
p-orbitals
Shape/Type
of Orbital
d-orbitals
f-orbitals
3. Third Quantum Number, ml (Magnetic Quantum Number)
- identifies the direction of orientation of the orbital with respect to external magnetic fields
Type of Orbital
Value of l
(0 to n-1)
Values of ml
( -l to +l)
4. Fourth Quantum Number, ms (Electron Spin Quantum Number)
- An electron can spin clockwise or counterclockwise.
- Spin can be indicated either through the use of +1/2 or -1/2
Total Number of Orientations
Summary of Quantum Numbers:
Orbital
ENERGY
l
Notation
LEVEL(n)
ml
(-l to +l)
Number of
Orbitals in
Subshell
Total
Number of
Orbitals
In Shell
Total
Number of
Electrons
In Shell
(2n2)
*You are NOT responsible for knowing COLUMNS 2 AND 4.
*A “2s” orbital is larger than a “1s” orbital, but they have the same shape (spherical).
*A “2p” orbital is made up of 3 “figure 8” shaped orbitals on a 3 axis system: px, py, and pz. All have the _________ shape, size and
energy, but each points in a different direction depending on the axis it is situated on; that is, they all have a different _____________
in space around the nucleus of the atom.
ATOMIC STRUCTURE AND THE PERIODIC TABLE
*Energy Level Diagrams/Electron Configurations
Examples: a) Draw the energy level diagram for CALCIUM.
b) Write the electron configuration for CALCIUM.
*Remembering the Electron Order of Filling:
Electron order of Filling Animation: http://intro.chem.okstate.edu/WorkshopFolder/Electronconfnew.html
Method 1: Using a Diagonal Orbital Diagram
 The diagram should be read as follows:
 1s < 2s < 2p < 3s <
Method 2: Using the Periodic Table….learn this one!!
*Examine the following periodic table. How can the periodic table be used to determine the electron order of filling?
s-block elements  Groups  ____ and _____ (i.e. the alkali metals and alkaline earth metals)
d- block elements  Groups ____ to _____ (i.e. the transition metals)
p-block elements  Groups  ____ to _____
f-block elements  Groups  _______________ and ________________(i.e. the inner-transition metals)
*PRINCIPLES AND RULE(…memorize these)
1.
___ Principle: Place electrons in the __________ energy orbital available until all electrons are “used up”. (“aufbau”
is German for building up)
2.
______ Principle: No two electrons can have the ________ four quantum numbers. Therefore, electrons in
the same orbital must have opposite spins. (+1/2 or –1/2)
3.
____ Rule: Electrons in the same orbital sublevel will not pair up until all magnetic orbitals of that orbital are at least
_________ filled (i.e. have at least one electron in them)
Writing Electron Configurations of IONS:
A. For ANIONS, ________ the appropriate # of electrons and account for these electrons when writing the electron configuration.
e.g. Write the electron configuration for:
i) fluorine 
*fluoride (9 e- + _____ = F-) 
ii) sulfur 
*sulfide (16 + _____ = ____)
iii) phosphorus 
*phosphide (15 + _____ = ____) 
B. For CATIONS, ____________ from the orbital with the _____________ principle quantum number(energy level)!!!....remove
from 4s before 3d, for example!
e.g. Write the electron configuration for:
1. a) Fe 
2. a)
Sn 
b) Fe2+ 
b)
Sn2+ 
c) Fe3+ 
c)
Sn4+ 
Writing SHORTHAND Electron Configuration Using the Periodic Table Method
*You are expected to be able to write long and shorthand configurations for elements up to and including iodine.
Step 1  Write the symbol for the ______________ noble gas in square brackets.
Step 2  Add unaccounted for orbitals/electrons.
e.g. Write the shorthand electron configuration for:
i) Magnesium
iii) Iodine


ii) Chlorine
iv) Bismuth


Another Way to Represent Configurations  Orbital Diagrams:
Anomalous (i.e. irregular) Electron Configurations
e.g. Draw the expected and actual electron configurations for i) copper and ii) chromium using valence shell orbital diagrams.