Quantum Theory
Beyond Bohr
What we know from Bohr
• Bohr came up with the (at the time) radical idea
that electrons orbit around the nucleus.
• He said that energy could only change in little
“jumps” (quantas) – which led us to Quantum
Mechanics
Quantum Mechanical Model
There are four quantum numbers:
Principle Quantum
Number (n)
Describes the location of the electron –
represent the energy level of the electron
-- From n=1, 2, 3, 4….
Azimuthal Quantum
Number (l)
Also describes an electron’s location – more
specifically the orbital where the electron is
-- From l = 0, 1, 2, 3…
Magnetic Quantum
Number (ml)
Describes the electron’s location within the
orbital.
-- From –l to +l
Spin Quantum Number
(ms)
Describes the spin of the electrons in the
orbital.
-- +1/2 or -1/2
Azimuthal Quantum Number
l = 0 describes an s-orbital
p-orbitals
l = 1describes the p-orbitals
There are 3 p-orbitals.
d-orbitals
l = 2 describes the
d-orbitals
There are 5 d-orbitals
f-orbitals
l = 3 describes the f-orbital
There are 7 f-orbitals
So how does Quantum Theory Work?
• An electron’s position can be determined if
the quantum numbers are known.
• For example:
Where is an electron with the following
quantum numbers located?
- n=2, l=1, ml=+1
Answer: 2p orbital, 3rd “space”
So what else can you do with it?
• You can count the electrons in an
atom…beyond the usual 3 orbitals (or 18
electrons)
Orbital
s
Maximum
Number of
electrons
s-orbitals are at all
energy levels.
2
p
6
d
10
f
14
p-orbitals begin at
n=2
d-orbitals begin at n=3,
f-orbitals begin at n=4
Orbitals - according to energy