Quantum Model: Energy Levels & Where the Electrons Hang Out
Bohr’s model of the atom represented the electron energy
levels as orbits in the electron cloud with the electrons orbiting
the nucleus much like the earth and other planets orbit the
sun. This model explained the emission spectrum for
hydrogen, BUT …
it didn’t explain the emission spectrum for other elements.
Schrodinger and Heisenberg used the principles of waves and
mechanics, and complex mathematical equations to develop a
new model of the atom. Their model of the electron energy
levels more accurately represented the emission spectrums for
all the elements. The model is known as the quantum model.
Bohr Model
Quantum Numbers – 4 numbers describe the location of the electron
1 - Principle Quantum Number, n
 more commonly known as the main energy level or
shell that surrounds the nucleus
 an infinite number of energy levels
 the electrons of all of the known elements can fit in
the first 7 energy levels
 from n=1 (lowest) to n=7 (highest)
2 - Orbital Quantum Number, l
 orbitals are sublevels within the main energy levels
 s, p, d and f (low to high energy)
 describes the shape of these energy sublevels
 electrons are located in the orbitals
 all main energy levels have an s orbital
 not all energy levels have the other 3 orbitals
3 - Magnetic Quantum Number, m
 describes the orbital’s orientation in 3-D space
 specifies how many orbitals are in each sublevel
4 - Spin Quantum Number, s
 describes the electron’s spin, + ½ or – ½
 each orbital holds 2 electrons of opposite spin
Summary Table of Energy Levels, Orbitals & # of Electrons
Main Energy
Level , n
1
I n cr ea sin g En er g y
2
3
4
Sublevels
(n sublevels)
# of Orbitals
per Sublevel
# of Orbitals per
Main Level, n2
# of Electrons
per Sublevel
# of Electrons per
Main Level, 2n2
s
1
1
2
2
s
1
p
3
s
1
p
3
d
5
10
s
1
2
p
3
d
5
f
7
4
2
6
8
2
9
16
6
6
10
18
32
14
Filling the Orbitals with Electrons
 Electrons fill orbitals starting with the lowest energy sublevel, then the next higher energy sublevel, and so on.
 Because of the complex shapes of the orbitals the main energy levels can overlap.
 Example: the 4s sublevel is lower in energy than the 3d sublevel.
Sublevels arranged by energy level. Electrons fill
sublevels in order of increasing energy beginning
with sublevel 1s.
The diagram above shows the “diagonal rule”.
Electrons fill orbitals starting at the far right hand
column and moving diagonally to the far left
column, and then moving to the far right column.