Pauli Exclusion Principle – Definition
● Each orbital can hold TWO electrons but must have opposite spins.
●
No two electrons in an atom can have the same four quantum numbers.
●
Each e- has a unique “address”:
○ Principal # (n): energy level
○ Ang. Mom # (I): sublevels (s,p,d,f)
○ Magnetics # (m11): orbital
○ Spin # (ms or s): electron
Aufbau Principle –
● Electrons fill the lowest energy orbitals first.
● “Lazy Tenant Rule”
Hund’s Rule –
● Within a sublevel, place one e- per orbital before pairing them.
Quantum Numbers –
● Specify the “address” of each electron in an atom
Quantum
Number
n
l
Allowed Values
n = 1, 2, 3, ......
l = (n-1), (n-2), ...., 0
0=s, 1=p, 2=d, 3=f
Name and Meaning
Principal quantum number: orbital energy and size.
Azimuthal (or orbital) quantum number: orbital shape (and energy in a multi-electron
atom), letter name for subshell (s, p, d, f)
ml
ml = l, (l-1), ..., 0, ..., (-l+1), -l
Magnetic quantum number: orbital orientation
ms
ms = 1/2, -1/2
Electron spin quantum number: spin up (+) or spin down (-).
2
2
6
1𝑠 2𝑠 2𝑝
S
− 𝐶𝑜𝑟𝑒 𝐸𝑙𝑒𝑐𝑡𝑟𝑜𝑛𝑠
16e-
[Ne] 3s2 3p4
2
4
3𝑠 3𝑝 − 𝑉𝑎𝑙𝑒𝑛𝑐𝑒 𝐸𝑙𝑒𝑐𝑡𝑟𝑜𝑛𝑠