Chapter 1.10-1.13: Molecular Dipoles and Forces
What should be considered when evaluating molecules to determine which has a higher boiling point?
Consider the following factors: Are there dipole-dipole interactions (BP↑)? Will it form hydrogen bonds (BP↑)? Which of the two molecules has more carbon atoms (BP↑)? If similar in carbon numbers, is there branching (BP↓)? Finally, if all other aspects are similar look for a substantial difference in weight (BP↑).
Draw the Lewis structure for HCOOH and predict the hybridization state, molecular geometry and approximate bond angle around the central atom.
sp² , trigonal planar, 120⁰
Name the three intermolecular forces and list them in order of increasing strength.
1. London Dispersion Forces (weakest) 2. Dipole-Dipole Interactions 3. Hydrogen Bonding (strongest)
Determine which of the following has the lowest boiling point: CH₃Cl , CH₄ or CCl₄
CH₄ has the lowest boiling point because it only has london dispersion forces. CH₃Cl and CCl₄ have london dispersion forces and dipole-dipole interactions.
Which of the following compounds has the larger dipole moment? Explain your choice. CO₂ or NCl₃
CO₂ has linear geometry and the dipole moments cancel out, therefore it has NO molecular dipole. However, NCl₃ has a dipole pointing towards the lone pair of electrons giving it an overall molecular dipole.
Draw NH₃ using the correct geometry. Identify the following in your drawing: steric number, hybridization, total sigma bonds, type of molecular geometry.
Hybridization of N = sp³
Which of the following molecules would have hydrogen bonding? Explain your answer. CH₄ or H₂O
H₂O has hydrogen bonding. Hydrogen bonding occurs when a positive dipole on hydrogen is attracted to a negative dipole on a lone pair of electrons on F, O or N. Water has an oxygen with a lone pair in which the hydrogen from another water molecule can be attracted to.
What is the hybridization state, molecular geometry and approximate bond angle for CH₃⁺?
It is sp², has trigonal planar geometry and a bond angle of 120⁰.
Describe how soap can remove oil stains from clothing.
Soaps form clusters called micelles. The polar groups of the soaps form the surface of the micelle and hydrogen bond to the surrounding water. The interior of the micelle is composed of the nonpolar, hydrophobic portions of the soap molecules. Grease and dirt are nonpolar and have limited solubility in water. In soapy water however, grease and dirt will dissolve in the nonpolar interior of the soap micelles, which in turn are soluble in the water.
According to the VSEPR theory, what are the basic electron pair arrangements for steric numbers 2-4?
Steric #2 - Linear Steric #3 - Trigonal Planar Steric #4 - Tetrahedral The above bond angles will vary slightly due to the number of lone pairs causing greater repulsion.
If the steric number is a 2, identify the type of hybridization and draw an example of a hydrocarbon with that hybridization.
Steric #2 = sp
If the steric number is a 3, identify the type of hybridization and draw an example of a hydrocarbon with that hybridization.
Steric #3 = sp²