Molecular Shape and Molecular Orbitals

VSEPR Model or Valance Shell Electron Pair Repulsion Model is an important concept to determine the shape of the molecules. There are several common shapes of molecules that we have to concern:

VSEPR Geometric Shape and Angle
Source: http://chemistry.ncssm.edu/labs/molgeom/index.html

Molecular Orbitals 

To determine the existence of the molecules, we consider the actual overlapping between molecules or between atoms
Some Rules are important in order to get the correct orbital population

1. Always fill the electrons up in the lowest energy orbital 
2. 2 electrons are maximum in each orbital, and two electrons are represented by two antiparallel arrows  

We only focus on the atoms in periodic 1 and 2 in this level: 

Anti-bonding orbitals always have star superscript 

Bonding orbitals always have the lower energy level than Anti-bonding 

General Orbital Diagram for Period 2 Elements
Source: http://universe-review.ca/F12-molecule.htm

This is the diagram only apply for O,F, Ne. Notice that the 2p bonding orbitals have a different arrangement from the anti-bonding orbital. 

Orbital Diagram for O,F, and Ne
Source: http://bobcatchemistry.wikispaces.com/AP+Chem+Lab+7

Bond Order and Bond Length 

The orbitals can help us to predict the stability of the molecules by the Bond Order 

Bond Order Formula

The number of bond order represents the molecules have single, double, triple bonds (or different fractions based on the molecules)

Moreover, with bond order, we can determine the bond length between the molecules: 

the higher the e cell, the more easily reduced

Source: Lectured by Professor Eric Bullock