Electron Configuration
Peg Ellis
INTRODUCTION
Modern Atomic View:
The world of the atom is made
up of waves and probability,
The speed and location are
subject to uncertainity.
ELECTRON ORBITALS
Heisenberg Uncertainty Principle
It is impossible to know with
certainity both the location
and the velocity of an
electron.
Bohr Diagrams
Diagrams are useful for counting
electrons and illustrating different
energy levels.
Worthless as pictures of what
atoms really look like.
This solar system model uses orbits
To show where the electrons are.
Electrons do not orbit the nucleus.
They live in regions of space called
Orbitals. Orbitals are organized by
the energy level or shell that they
belong to.
They are clouds of probability.
An orbital is the shape of the
region of space where an electron
is most likely to be found.
This ball-shaped orbital is hydrogen.
The dots represent possible positions
of the one electron hydrogen has.
1s orbital
Notice there are more
dots near the center of
sphere than near the
edges.
ANALOGY:
Bird feeder on a pole with birds
migrating south surrounding the
feeder. Blue spots could be a bird
at any given time. Spherical shape
2s Orbital
Also shaped spherical.
The difference:
Larger and higher energy than the
1s orbital.
SHAPES OF ORBITALS
• 2s orbital
Spherical
2p orbital
double lobed
3d orbital
complex
There are also f orbitals- very complex
ENERGY LEVELS
The more energy- the farther away
the shell is from the nucleus
1st shell=one type of orbital= s
2nd shell = two types = s,p etc….
Principal Quantum Number
• The energy levels or shells are
distinguished by their number.
• This number is called the principal
quantum number.
• Each energy level have specific
Names. N1 =only 1s orbital
N2 = 2s and 2p orbitals
N3= 3s, 3p, and 3d orbitals
Energy Levels
n=1
n=2
n=3
n=4
How many electrons can be in a sublevel?
Remember: A maximum of two electrons can
be placed in an orbital.
s orbitals p orbitals d orbitals f orbitals
Number of
orbitals
Number of
electrons
1
2
3
5
7
6
10
14
ELECTRON RULES
Aufbau Principle – from bottom up
Hund’s Rule – singles first
Pauli Exclusion Principle – opposites
only
From the Bottom Up: Rooms must be filled
from the ground floor up. Fill the one room on
the first floor before starting to put new
tenants on the second floor. Then fill the s
room before the p rooms. At higher floors
the order might change a bit.
Aufbau Principle: the electrons fill the
available orbitals from lowest energy to
highest energy. In the ground state all
the electrons are in the lowest possible
energy level.
Singles First: the owner of the building wants
to have the tenants spread out as much as
possible. For that reason singles are placed in
rooms before couples. If couples must be placed
into a room then all of the other rooms on that
floor must already have a single in them.
Hund’s Rule: The electrons must be
placed into the orbitals in such a way that
no pairs are put together unless absolutely
necessary. That is, single electrons
must be placed into boxes first and then
paired up if necessary.
SHORTHAND NOTATION
1s2 1 = quantum number
(energy level)
s= s- type orbital
2= electrons
2p6 = 2nd quantum number,
p type orbital,
6 electrons
Electron Configurations
4
2p
Energy Level
Number of
electrons in
the orbital
Orbital
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6
6s2 4f14… etc.
Electron Configuration Order
Notice that 4s orbital fills
Before the 3d orbital.
This is because 4s is actually
slightly lower in energy than
the 3d orbitals.
Arrow direction
Represents electron
Spin. Clockwise and
counterclockwise
What is the element?
1s22s22p63s23p64s23d104p65s1
Rubidium – 37 electrons
What is the element?
{Kr} 5s1