Electron Cloud Structure

Structure of the Electron Cloud
Electron Distribution: The Results of
the Mathematics of Quantum
Mechanics

Levels of Organization
• The term, ‘electron cloud’ doesn’t tell us
very much about electron location.
• This cloud is actually highly structured.
• It is divided into:
– Principal energy levels (PELs or shells )
• Energy sublevels (or subshells)
–Orbitals

PEL Review
• Atoms may have from 1-7 PELs that are
concentric spheres.
• Level 1 is closest to the nucleus and
level 7 found only with the largest
atoms is the highest PEL.

Energy Sublevels
• Principal energy levels are subdivided
into 1-4 sublevels, depending on how
large the PEL is.
• Sublevels are designated as s, p, d and
f.
• Each sublevel has a different number of
orbitals, and the orbitals have different
shapes.

Orbitals
• An orbital is the region of space where
there is a 90% probability of finding an
electron of a particular energy.
• A single orbital may be home to 1 or 2
electrons, but never more than 2.

The ‘s’ sublevel
• The ‘s’ sublevel is the simplest.
• It has only 1 orbital, which is a sphere.
• The orbital can house 2 electrons.

Reality
• Please keep in mind that
orbitals are not solid
shapes as the previous
picture suggests. The
sphere represents 90%
electron density.
• A real orbital would
probably have a fuzzy
appearance, more like
this.

The ‘p’ sublevel
• The ‘p’ sublevel is larger
than the ‘s’ and consists
of 3 orbitals which each
look like this.
• The p-orbital is bi-lobed
and can also house 2
electrons.
• The grey circle in the
center represents the s-
orbital.

The ‘p’ sublevel
z
• The ‘p’ sublevel
consists of 3 orbitals,
each at right angles
to each other in
space.
• Thus, the entire
sublevel can hold up
to 6 electrons total.
y
x

The ‘p’ sublevel
z
• The 3 orbitals of
the p-sublevel are
designated as p x ,
p y and p z for the
3 axes upon
which they lie in
space.
y
x

The ‘d’ sublevel
• The ‘d’ sublevel consists of 5 orbitals
whose shapes are more complex.
• The sublevel can house 10 electrons.
• The orbitals have 2 different types of
shapes, and are oriented in space so as
not to overlap each other.

d- orbitals
• Four of the d-
orbitals look like
this.
The fifth d-orbital
looks like this.

‘d’ sublevel
• Altogether, the d-
orbitals occupy a
common space,
but do not
overlap each
other.
• The whole
sublevel looks like
this.

‘f’ sublevel
• The ‘f’ sublevel has 7 orbitals, home to 14
electrons and is much more complex.
• The orbitals look like this.

Heisenberg Uncertainty Principle
• The whole idea that electrons occupy 3-
dimensional volumes of space came
from Werner Heisenberg who said that
was impossible to know both the speed
and location of tiny, fast-moving
electrons at the same time.
• This became know as the
“Heisenberg Uncertainty Principle.”

Heisenberg Uncertainty Principle

Pauli Exclusion Principle
• Another famous
physicist, Wolfgang
Pauli stated that a
single atomic orbital,
regardless of size or
shape can only hold
2 electrons, and
those electrons must
have opposite spin.

Electron Spin
• Like charge, particles
have another quality
called ‘spin.’
• There are only 2
possible values,
parallel (up) or antiparallel
(down).

Putting It All Together
• PEL 1 is small and ‘close’ to the nucleus.
• It only has 1 sublevel, an ‘s’ and so has
room for only 2 electrons.
• When the 1 st PEL is filled with 2 e - , the
next electrons must go into the 2 nd PEL.

Putting It All Together
• The 2 nd PEL is larger, and so has room
for more electrons.
• It has an ‘s’ sublevel, and a ‘p’ sublevel.
• The ‘s’ has room for 2 e - while the ‘p’
sublevel with its 3 orbitals, has room for
6 more, giving a total of 8 electrons in
the 2 nd PEL.

Atomic Models
• Perhaps now it is easy to see where
those Bohr models of the atom are
coming from. Easy to understand, but
not accurate.

Putting It All Together
• PEL 3 is larger still, and has room for a
greater number of electrons.
• It has s, p and d sublevels.
• The ‘s’ sublevel can hold 2 e - , the ‘p’
can hold 6, and the ‘d’ can hold 10 (5
orbitals) for a total of 18.

Putting It All Together
• PELs 4-7 all have s, p, d, and f possible
sublevels.
• s 2 e - (1 orbital)
• p 6 e - (3 orbitals)
• d 10 e - (5 orbitals)
• f 14 e - (7 orbitals)
• Total of 32 electrons.

A Helpful Table
PEL
1 2 3 4 5-7
Sublevels
s s / p s p d s p d f Same as
4
Orbitals
In
Sublevel
e- in
sublevel
Total e- in
PEL
1 1 / 3 1/3/5 1/3/5/7 Same as
4
2 2 / 6 2/6/10 2/6/10/14 Same as
4
2 8 18 32 Same as
4