Chemistry Notes
Electron Configurations
The Bohr Model
In the early 1900’s Niels Bohr
introduced the concept of energy
levels, where the electrons orbited
similar to the way the planets orbit
the sun.
Quantum Mechanical
Model
In 1926, Erwin Schrodinger used
the new quantum theory to write
and solve mathematical equations
to describe electron location.
The Quantum Mechanical
Model, cont.
Today’s model comes from
the solutions to
Schrodinger’s equations.
Where are the electrons?
In an atom, principal energy
levels (n) can hold electrons.
These principal energy levels are
assigned values in order of
increasing energy (n=1,2,3,4...).
Where are the electrons?
Within each principal energy level,
electrons occupy energy sublevels.
There are as many sublevels as
the number of the energy level
(i.e., level 1 has 1 sublevel, level 2
has 2 sublevels, etc.)
Where are the electrons?
There are four types of
sublevels—s,p,d and f. Inside
the sublevels are atomic orbitals
that hold the electrons. Every
atomic orbital can hold two
electrons.
Orbital Shapes
Where are the electrons?
S has one orbital, P has
three, D has five and F has
seven. How many
electrons can each one
hold?
Where are the electrons?
Where are the electrons?
Where are the electrons?
Electron Configuration
In the atom, electrons and the
nucleus interact to make the
most stable arrangement
possible.
Electron Configuration
The ways that electrons are
arranged around the nucleus
of an atom is called the
electron configuration.
Electron Configuration
The electron configuration is
similar to an “address” for
each electron in an atom.
Electron Configuration
For example, the electron
configuration for Helium is:
2
1s
1 = the energy level
s = the sublevel
2 = the number of electrons
Electron Configuration
For example, the electron
configuration for Oxygen is:
2
2
4
1s 2s 2p
Electron Configuration
What do you get when you add
up the superscripts from
Oxygen’s electron configuration?
2
2
4
1s 2s 2p
Electron Configuration
What do you get when you add
up the superscripts from
Oxygen’s electron configuration?
2
2
4
1s 2s 2p
What does the number 8
tell you?
Electron Configuration
Which element has the following
electron configuration?
2
2
6
1
1s 2s 2p 3s
Electron Configuration
Which element has the following
electron configuration?
2
2
2
1s 2s 2p
Electron Configuration
Which element has the following
electron configuration?
2
2
6
2
5
1s 2s 2p 3s 3p
Electron Configuration
Write the electron configuration
for Magnesium.
Electron Configuration
Write the electron configuration
for Nitrogen.
Electron Configuration
Write the electron configuration
for Potassium.
Electron Configuration
So far, we have only been
working with elements in the S
& P sublevel sections on the
periodic table.
Electron Configuration
When you write electron
configurations for elements in
the D sublevel section, the
energy level is one number less
than the period the element is
in.
Electron Configuration
Why does this happen?
To put it simply, the D sublevel
is very large and complicated.
It overlaps with the other
sublevels, so just know it’s one
number less than what the
periodic table shows.
Electron Configuration
For example, the electron
configuration for Iron is:
2
2
6
2
6
2
6
1s 2s 2p 3s 3p 4s 3d
Electron Configuration
What do you get when you add
up the superscripts from Iron’s
electron configuration?
2
2
6
2
6
2
6
1s 2s 2p 3s 3p 4s 3d
You get 26!
Electron Configuration
Which element has the following
electron configuration?
1s22s22p63s23p64s23d104p65s24d9