8-3 Resonance When there is more than one way to write the formula for a molecular compound, the compound exists in all of those forms...this is called resonance.

Expanded Octets and Exceptions PCl and SCl are exceptions because they have more than 8 electrons on the central atom. BF3 has only 6 electrons on the central atom...B is a smaller atom and allows this.

Other Octet Exceptions

8-4 Molecular Shapes VSEPR is valence shell electron pair repulsion and causes molecules to take their shapes.

8-5 Electronegativity and Polarity Electronegativity is the strength of pull by one atom on an adjacent atoms electron. Bond polarity can be determined by subtracting the electronegativity of adjacent atoms. Difference of... 0-.3999 is non-polar covalent .4-1.6999 is polar covalent >1.7 is ionic

Polar Molecules If a molecule has polar bonds and 2 or more different ends, it is a polar molecule. Remember the rule like dissolves like... polar compounds dissolve polar substances.

Network Solids Most molecular compounds are gas or liquid, at room temperature, with low melting points. Network solids are molecular compounds that have a crystalline structure and high melting points.`