OBJ - Water: Solvent of Life

Question 1

Distinguish between covalent bonds & noncovalent forces & what determines the polarity of a molecule?

Answer 1

• Covalent Bonds: Share electrons, similar electronegativities (nonpolar)
** Polarity occurs when unequal EN/unequal sharing/partial charges, electrons spend greater proportion of the time in one area
• Noncovalent interactions: No sharing, but an exchange of electrons (ionic bond)

Question 2

List the 4 major types of covalent forces & explain their molecular basis

Answer 2

1. Electro- Ionic interaction
   (Na+ & Cl-)
2. Dipole-Dipole interactions & Hydrogen bonding (Permanent dipole)
3. Hydrophobic interactions
   (polar molecules with nonpolar = oil & water)
4. London Dispersion/Van der Waal Forces (Induced Dipole)

Question 3

Discriminate polar molecules from nonpolar compounds

Answer 3

• Polar molecules & ion’s cannot pass through lipid bilayer because of the nonpolar FA chains -> need channels
• Water – needs channel because polar
• NP molecules can diffuse

Question 4

Describe the fundamental basis of hydrogen bonding

Answer 4

• Oxygen has 2 unpaired sets of electrons

- Partial negative charge on oxygen’s end “pseudo bonds” with the partial pos on another’s partially negative H end

Question 5

Describe hydrogen bonding & give exmaples of donors & acceptors & give examples

Answer 5

• Due to big EN difference & relative size
• Need to have and H-N, H-O, or H-F
• NOF are electron donors
• H’s are electron revievers

Question 6

What is an induced dipole & what is its origin? How does it contribute to Van der Waals/London dispersion forces?

Answer 6

• Consists of an ion and a non-polar molecule interacting. Like a dipole-induced dipole force, the charge of the ion causes distortion of the electron cloud on the non-polar molecule
• Proportional to surface area (length of FA chain), shape & nucleus/charge not being exactly at the center
• many induced dipoles Σ Van der Waals (induced dipole) vs Electrostatic interaction (cations & anions)

Question 7

Define amphipathic molecules & how they interact with water

Answer 7

• Both a Hydrophilic/Polar part (head) & a Hydrophobic/nonpolar part in the same molecule (tail)
• Hydrophilic: Polar head can interact with water & H bond
• Hydrophobic: Nonpolar end/FA chain does not
• Phospholipids – stay happy by making bilayer so that nonpolar tails are interacting with themselves & polar heads are interacting with aq environment -> micelles

Question 8

** What are the solubilities of Ionic, Polar & nonpolar molecules in water?

Answer 8

Nonpolar - Insoluble
Polar - Soluble (solvated by H bonding)
Ionic - Soluble (solvated by H bonding)