Chapter 2

Question 1

Why Hybridization?

Answer 1

• 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

Question 2

Molecular Distortions

Answer 2

• 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

Question 3

Consitutional Isomers

Answer 3

• 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.

Question 4

Stereoisomers

Answer 4

• 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.

Question 5

cis

Answer 5

same side

Question 6

trans

Answer 6

on different sides

Question 7

Effect of branching on boiling point

Answer 7

• 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.

Question 8

Hydrogen Bonding

Answer 8

• 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.

Question 9

Polar Solute in a Polar Solvent

Answer 9

Dissolves - Hydration releases energy; entropy increases.

Question 10

Polar Solute in Nonpolar Solvent

Answer 10

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

Question 11

Nonpolar Solute with Nonpolar Solvent

Answer 11

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

Question 12

Nonpolar Solute with Polar Solvent

Answer 12

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.