Electron Configuration
Where do the electrons really hang out??
In those crazy orbitals!!
EC = The arrangement of electrons
around a nucleus.
Let’s use the orbital
shapes to place
electrons.
Helium
Oxygen
Not sure about you…
I think that is a royal pain!
There is an easier way- Electron
Configuration!

There are seven energy levels (we only worry about the
first 4).

Within the levels are subshells (s, p, d, f)

Each subshell can accommodate a certain number of
orbitals

Each orbital can contain 2 electrons
Electron Configuration

3 Rules:
 Aufbau
Principle
 Pauli Exclusion Principle
 Hund’s Rule
Molecular Orbital
diagrams…
Helium
Oxygen
Aufbau Principle

Electrons enter the lowest energy
level first

Different levels within a principal
energy level can overlap the
energy levels of an adjacent
principal level

The filling of atomic orbitals does
not follow a simple pattern.
Aufbau PrincipleHere’s the pattern!!
1s
2s
3s
4s
5s
2p
3p 3d
4p 4d 4f
5p 5d 5f
Pauli Exclusion
Principle



An atomic orbital may
describe at most 2 electrons
1 or 2 electrons may occupy
an orbital
When an orbital contains
2 electrons, they must have
an opposite paired spin
Pauli Exclusion
Principle

Because of their magnetic
moments, we generally represent
electrons using a single barbed
arrow. The tip of the arrow points
to the magnetic north of the
electron
Hund’s Rule

When electrons occupy orbitals of equal energy
(s, p, d, f), one electron enters each suborbital
until all orbitals contain 1 electron with the same
parallel spin

The second electrons then add to each orbital
so that their spins are paired.
Heisenberg Uncertainty Principle
“The more precisely the
position is determined, the
less precisely the momentum
is known in this instant, and
vice versa.”
It is impossible to know the
velocity and position of the
electron at the same time.
Lets do the EC for using the
rules! (Show MO and EC)
Fluorine
Sodium
Do WS Level 1 using MO diagrams
Some things to note
Valence electrons are those in the
outer s and p orbitals.
Shared and unpaired electrons can
be determined by looking at the
outermost, incomplete orbital.
We can just use Aufbau– it is
a little easier
Oxygen
1s
2s
3s
4s
5s
2p
3p 3d
4p 4d 4f
5p 5d 5f
Silicon
Calcium
Now try the Level 2
WS
Work on your Valence
electron WS for 10
minutes!
Compare answers, discuss what you may
be doing wrong.
Questions for me?
Warm Up
Can we tell which element
by looking at the EC?
1s22s22p63s23p5
1s22s22p63s23p64s2 3d10
How did you do
Count the number of electrons
1s22s22p63s23p5 = 17 electrons, Chlorine
1s22s22p63s23p64s2 3d10= 30 electrons, Zinc
Did you write this in
your notes?
Valence electrons are those in the
outer s and p orbitals.
Shared and unpaired electrons can
be determined by looking at the
outermost, incomplete orbital.
Molecular Orbital DiagramsUse lines to show orbitals
Li
1s
2s
3s
4s
5s
2p
3p 3d
4p 4d 4f
5p 5d 5f
Phosphorus
Vanadium
Go over some on the
Valence electron WS
We can also use the
periodic table to
determine EC.
Try some more of the WS using the
periodic table method…
Get out a half sheet of
paper…
I will project the quiz as soon as the
bell rings.
Be sure you write very neat!!
Noble Gas
Configuration…
Write the noble gas in the period
above the element… add the rest of
the electron configuration.
Example:
Long form for Phosphorus: 1s22s22p63s23p3
Noble Gas Configuration for Phosphorus
Nobel gas above P = Ne
[Ne] 3s23p3
You need to be careful which
periodic table you use for this!!
The Web-Elements PT works well…
Now you try!
Write the noble gas configuration for
V (atomic #23)
La (atomic #57)
Lr (atomic #103)
Now you try!
V (atomic #23)
La (atomic #57)
Lr (atomic #103)
Now you try!
Write the noble gas configuration for
V [Ar] 4s23d3
La [Kr]6s24f1
Lr [Xe] 7s24f146d1
Molybdenum (42)
1s22s22p63s23p64s23d104p65s14d5
Th (90)
[Rn] 7s25f2
Ground, Excited or Impossible?
Ground- If the electrons are in the orbitals
that you would expect them to be in.
Excited- If some of the electrons are in a
higher energy level.
Impossible- If the orbital doesn’t exist
and/or the EC doesn’t make any sense.
Ground, Excited or Impossible?
Chlorine- 17 electrons
1s22s22p63s23p5
1s22s22p63s13p34s24p1
1s22s22p63s13p42d2
Ground, Excited or Impossible?
Zinc- 30 electrons
a. 1s22s22p63s23p64s23d86s2
b. 1s22s22p63s23p64s13d44p7
c. 1s22s22p63s23p64s2 3d10
You try…
Write the electron configuration for
carbon…
Write an electron configuration for an
excited atom.
Write an impossible EC…
Have your neighbor check your work.
Questions on the
HW?
What happens with
Ions??
Ions gain or lose electrons…
What is the electron configuration for
the magnesium cation?
What about S2-
When removing
electrons …
Remove the last electrons that were
placed…
Unless there are electrons in the d
orbital…then remove the last s
electrons first.
Isoelectronic…
Different atoms that have the same
electron configuration.
Na1+
Ne
F1-
Identify the atoms
An element that has a 2- charge that is
isoelectronic with Neon.
Identify the atoms
An atom that has lost 3 electrons and is
isoelectronic with He
Identify the atoms
An element that has a 2- charge that
is isoelectronic with Neon.
An atom that has lost 3 electrons
and is isoelectronic with He
An atom that has gained one
electron and has the same EC as
Cu.
Test