Chapter 2

• Electron density in hybrid orbitals has a more defined direction - This provides for better orbital overlap in bonding • better overlap = stronger bonds = shorter bonds • bond strength is related to % s-character

• VSEPR predicts bond angles for ideal geometries where all substituents are identical - non-identical groups distort the ideal angles - lone pairs more repulsive than bonding pairs - double bonds more repulsive than single bonds - electronegative atoms can be “compressed” - steric repulsions arise from group’s volume

• Constitutional isomers have the same chemical formula, but the atoms are connected in a different order. - Constitutional isomers have different properties. - The number of isomers increases rapidly as the number of carbon atoms increases.

• Stereoisomers are compounds with the atoms bonded in the same order, but their atoms have different orientations in space. • Cis and trans are examples of geometric stereoisomers and they occur when there is a double bond in the compound.

same side

on different sides

• The long-chain isomer (n-pentane) has the greatest surface area and the highest boiling point. • As the amount of chain branching increases, the molecule becomes more spherical and its surface area decreases. • The most highly branched isomer (neopentane) has the smallest surface area and the lowest boiling point.

• Strong dipole–dipole attraction. • Organic molecules must have NH or OH to be able to hydrogen bond with molecules of the same type. • The hydrogen from one molecule is strongly attracted to a lone pair of electrons on the oxygen of another molecule. • O—H more polar than N—H, so alcohols have stronger hydrogen bonding.

Dissolves - Hydration releases energy; entropy increases.

The solvent cannot break apart the intermolecular interaction of the solute, so the solid will not dissolve in the solvent.

The weak intermolecular attractions of a nonpolar substance are overcome by the weak attractions for a nonpolar solvent. The nonpolar substance dissolves.

If a nonpolar molecule were to dissolve in water, it would break up the hydrogen bonds between the water molecules. Therefore, nonpolar substances do not dissolve in water.