January 10, 2012
Erind Alushaj

How do Bonds Form?
Valence Bond/Atomic orbital model was developed by Linus Pauling in order to explain how atoms form molecules
Model says 2 orbitals overlap to make a ne combined orbital with opposite spinning electrons
This results in a decrease in energy of the atom forming the new bond
The shared electron pair is most likely found in between the two nuclei of the atoms bonding
*Hybridization was the only flaw to Pauling's Theory *

The VBT (Valence Bond Theory) can not explain most covalent, polyatomics or multiple bonds
VBT validity: simple molecules HF form with regular atomic orbitals and covalent bonds result from overlapping

Hybridization explains what VBT does not
Central atom makes new orbitals before bonding
New hybrid orbitals containing s, p, and d
Orbitals combining must be from the same energy level
For each hybrid orbital you need 1 atomic orbital
Orbital is named after what was added together ( 1 #s + 2 #p's = 1 #sp^2 )
New orbitals have equal energy and electrons may move to unoccupied orbitals

Hybrid orbitals are needed for
Sigma Bonds- 1 HO with 1 electron
Lone Pairs- 1 HO with 2 electrons
Co-ordinate covalent bonds- 1 HO with 2 electrons
*Pi bonds do not get HOs, but use atomic p orbitals with 1 electrons*

January 9, 2012
Erind Alushaj

Electron Configurations
electron configuration shows the specific placement of electrons within an energy level
sub level of energy levels are called orbitals and can hold a maximum of 2 electrons
there are 4 orbital types

s orbital --> single
p orbital --> group of 3
d orbital --> group of 5
f orbital --> group of 7

Every energy level has an s orbital, p starts at 2+, d starts at 3+, f starts at 4+
electrons are placed in lowest energy levels first
due to overlapping electron levels, some outer orbitals can be closer than inner ones (example 4s is closer than 3d)

H electron configuration 1s1
O electron configuration 1s22s22p4

Energy Level Diagrams
Show electron placement in the orbitals
Orbitals are represent lines or circles
Electrons are represented by upward and downward arrows or half arrows

Aufbau Principle: lowest energy levels are filled first
Hund's Rule: when there are multiple orbitals of equal energy, each orbital get a single electron before pairing up electrons
Pauli Exclusion Principle: when 2 electrons are placed in the same orbital, these electrons will spin in different directions

Quantum Numbers
are like the GPS for electrons
there are 4 numbers: n, l, ml, and ms

n is the principle quantum number and represents the energy level of the electron
l is the orbital shape number and represents the orbital type: s=0 , p=1 , d=2 , f=3
ml is the magnetic quantum number and tells which orbital the electron is in if there is a group of orbitals
possible values run from -l --> l (including 0)
ms is the spin number and tells the direction of the electron spin
(+1/2 if its the first electron and -1/2 if its the second)