Download Electron Configuration

The electron configuration of an atom is a form
of notation which shows how the electrons are
distributed among the various atomic orbital
and energy levels. The format consists of a
series of numbers, letters and superscripts.
2
1s
This electron configuration provides us
with the following information:



The large number "1" refers to the principle quantum
number "n" which stands for the energy level. It tells us that
the electrons of helium occupy the first energy level of the
atom.
The letter "s" stands for the angular momentum quantum
number "l". It tells us that the two electrons of the helium
electron occupy an "s" or spherical orbital.
The exponent "2" refers to the total number of electrons in
that orbital or sub-shell. In this case, we know that there are
two electrons in the spherical orbital at the first energy level.


The number of sublevels that an energy level
can contain is equal to the principle quantum
number of that level. So, for example, the
second energy level would have two sublevels,
and the third energy level would have three
sublevels.
is called an s
sublevel
is called a p
sublevel.
is called a d
sublevel
is called an f
sublevel.
Although energy levels that are higher than 4
would contain additional sublevels, these
sublevels have not been named because no
known atom in its ground state would have
electrons that occupy them.
Energy Level
Number of
sublevels
Names of
sublevels
1
1
s
2
2
s, p
3
3
s, p, d
4
4
s, p, d, f
5
5
s, p, d, f, g
Each type of sublevel holds a
different number of
orbitals, and therefore, a
different number of
electrons.
Space occupied by a
pair of electrons


s sublevels have one
orbital, which can
hold up to two
electrons.
p sublevels have three
orbitals, each of which
can hold 2 electrons,
for a total of 6.


d sublevels have 5
orbitals, for a possible
total of 10 electrons.
f sublevels, with 7
orbitals, can hold up
to 14 electrons.
Sublevel
# of orbitals
s
1
p
d
f
3
5
7
Maximum
number of
electrons
2
6
10
14




An easy way to calculate the number of orbitals
found in an energy level is to use the formula
n2.
For example, the third energy level (n=3) has a
total of 32, or nine orbitals.
This makes sense because we know that the
third energy level would have 3 sublevels;
an s sublevel with one orbital, a p sublevel with
3 orbitals and a d sublevel with 5 orbitals. 1 + 3
+ 5 = 9, so the formula n2 works!




An easy way to calculate the total number of
electrons that can be held by a given energy level
is to use the formula 2n2.
For example, the fourth energy level (n=4) can
hold 2(4)2 = 32 electrons.
This makes sense because the fourth energy level
would have four sublevels, one of each of the
named types.
The s sublevel hold 2 electrons, the p sublevel
holds 6 electrons , the d sublevel holds 10 electrons
and the f sublevel holds 14 electrons. 2 + 6 + 10 +
14 = 32, so the formula 2n2 works!
Max # = …n…
ENERGY LEVEL
MAX # OF ELECTRONS
1
2
3
4
5
2
8
18
32
50
2
2n
Where n is any energy level
A detailed way of showing the
order in which electrons fill in
around the nucleus
K
Bohr
Models
vs. e
Configs
2
2
6
1
6
2
K: 1s 2s 2p 3s 3p 4s
3
5f
Energy Level
# of e- in
sub-energy
level
Sub-Energy
Level
Number of electrons
in the sub level 2,2,5
2
1s
2
2s
5
2p
Sublevels
Blocks in the Periodic Table




Use the last noble gas that is located in the
periodic table right before the element.
Write the symbol of the noble gas in brackets.
Write the remaining configuration after the
brackets.
Ex: Fluorine: [He] 2s2 2p5

In 1925, Wolfgang Pauli stated: No two
electrons in an atom can have the same
set of four quantum numbers. This
means no atomic orbital can contain
more than TWO electrons and the
electrons must be of opposite spin if
they are to form a pair within an orbital.
The most stable arrangement of
electrons is one with the maximum
number of unpaired electrons. It
minimizes electron-electron
repulsions and stabilizes the atom.
In a set of orbitals, the electrons will
fill the orbitals in a way that would
give the maximum number of
parallel spins (maximum number of
unpaired electrons).
In large families with several children, it
is a luxury for each child to have their
own room. There is less fussing and
fighting if siblings are not forced to
share living quarters. The entire
household experiences a lower, less
frazzled energy state. Electrons find
each other very repulsive, so they too,
are in a lower energy state if each
“gets their own room” or in this case
orbital.
Electrons that are single occupants
of orbitals have parallel (same
direction) spins and are assigned
an up arrow.
Analogy: Students could fill each
seat of a school bus, one person at
a time, before doubling up.
The second electron to enter the
orbital, thus forming an electron
pair, is assigned a down arrow to
represent opposite spin.
Orbital notation is basically
just another way of
expressing the electron
configuration of an atom.
An orbital can hold only two
electrons and they must have
opposite spin.