Chapter 5
Models of the
Atom
Bohr’s model…
• Electrons are found in specific
circular paths (orbits) around the
nucleus.
• The electrons have fixed energies
called energy levels. (like rungs on a
ladder)
• The amount of energy required to
move an electron to another energy
level is called a quantum.
The Quantum Mechanical model
• It is based on the energy and possible
location of an electron.
• how likely it is to find an electron is
described in terms of probability. (ie.
Propeller blades)
• Based on work done by Shrodinger…
Atomic Orbitals
• The energy levels of electrons are labeled
by principal quantum numbers (n)
• Each energy sublevel corresponds to an
orbital of a different shape, which describes
where the electron is likely to be found.
Atomic Orbitals
Shapes and
Orientations of
Orbitals
1s Orbital
• Sphere around the nucleus
The one tells you that the electron
is in the orbital closest to the
nucleus
• S tells you about the shape
2s Orbital
• Similar to 1s except the electron is most
likely in the region farther from the nucleus
p Orbitals
• At the first energy level there is only the 1s
orbital, after the second energy level there
are 2p orbitals
• Look like dumbbells
• In the three directions
Remember….
MAX NUMBER OF ELECTRONS
IN AN ENERGY LEVEL
ENERGY LEVEL
MAX # OF ELECTRONS
1
2
3
4
5
2
8
18
32
50
Electron
Configuration
A detailed way of showing the
order in which electrons fill in
around the nucleus
# of
Electron Configuration
sub level
Symbols
e in
2
1s
Energy Level
Sub Level
(s, p, d, f )
We must follow 3 rules…
• Aufbau priciple
• Electrons occupy energy levels with lowest
energy first.
Pauli exclusion principle
• If 2 electrons occupy the same energy level
they must have opposite spins.
Hund’s rule…
• Electrons that occupy orbitals of the same
energy will have the maximum number of
electrons with the same spin.
• 2p
To start we will use orbital filling
diagrams to help us with electron
configurations….
• Example
Boron- has 5 electrons
Periodic table arrangement
s (n)
d (n - 1)
p (n)
1
2
3
4
5
6
7
f (n -2)
• the quantum theory helps to explain the
structure of the periodic table.
• n - 1 indicates that the d subshell in period 4
actually starts at 3 (4 - 1 = 3).
•Practice!!!
Summary: p orbitals and d orbitals
p orbitals look like
a dumbell with 3
orientations: px,
py, pz (“p sub z”).
Four of the d orbitals resemble two dumbells in a
clover shape. The last d orbital resembles a p
orbital with a donut wrapped around the middle.
st
1
Quantum #
Principle Quantum #
(n)
Specifies the energy level
that the electron is on.
nd
2
Quantum #
(l)
Specifies the shape of the
sub level .
The 3rd (m) and 4th quantum
numbers (s) …
• Deals with the orbital within the sublevel
and the spin of the electron.
Four Energy Sub-Levels
Energy Level
Sub-level
Type of sub
s
Sphere
2
# of
Orbitals
1
p
Dumbbell
6
3
d
4-Lobed
10
5
f
6-8 Lobed
14
7