Week 1: Electrons and
chemical bonding, LCAO-MO theory
Monday, 25, Wednesday, 27, and Friday, 29 August
2008, lecture 1 (pdf), lecture
2, lecture 3 (pdf)
Several of the depictions are from my German version of the book by
Harry B. Gray, Electrons and Chemical Bonding, Addison-Wesley Pub Co, 1964
(!)
... which you can get used on Amazon for a few Dollars (or borrow mine)
The same author also wrote a "newer version":
Chemical Bonds: An Introduction to Atomic and Molecular Structure
(Paperback), University Science Books, 1994
which costs $28 new or <$10 used.
Points/Topics to remember from this weeks classes:
- quantum
numbers
- n (shell), l
(orbital), ml (magnetic),
s (electron spin)
- elements
relevant for atmospheric chemistry (mostly those with n<=3 and groups 4
and up)
- Schrödinger
equation and atomic orbitals (AOs), l = 1, 2, 3, 4, … = s, p, d, f,
...; AO symmetry
- selection
rules, aka Pauli principle and Hund's rules
- Russel-Saunders
Terminology
- 2S+1L;
S = Σ s, L = Σ ml
- use capital Greek letter for MOs
- Linear
combination of atomic orbitals (LCAO) literally means
mathematically adding and subtracting AOs
- #x
AOs form #x molecular orbitals (MOs), a pair of AOs splits into a bonding
(b) and an anti-bonding (*) MO
- radially
symmetric MOs are named σ-orbitals, e.g. σb
- MOs
that transform into their mirror image after rotation are named
π-orbitals, e.g. π*
- all
filled MOs have spin = 0; only partially filled MOs contribute to spin ≠
0
- bonding
order = (#electrons in bonding MOs - #electrons in anti-bonding MOs)/2
- definition
of “radical”
- ground
states can be radicals