Polar Covalent Bonds & Formal Charges

• What is an ionic bond?

  One atom transfers electrons to another
• What is a symmetrical covalent bond?

  Two bonding electrons are shared equally
• What characterizes a polar covalent bond?

  Unequal sharing of bonding electrons
• What does δ represent in a polar covalent bond?

  Partial charge on atoms in the bond

  
• Why do atoms form polar covalent bonds?

  Due to differences in electronegativity

  
• What is electronegativity (EN)?

  Ability of an atom to attract electrons
• What happens when electronegativities differ by >2 units?

  Bonds are largely ionic
• What does a cross arrow indicate in a polar bond?

  Direction of bond polarity
• What is a dipole in a polar bond?

  It has a positive and negative end
• What does the dipole moment (µ) represent?

  Size of the dipole in a bond
• How is dipole moment calculated?

  Dipole moment (µ) = e x d
• What is the unit of dipole moment?

  Debye (D)

  
• What does a molecule with one polar bond have regarding dipole moment?

  Its dipole moment equals that of the bond
• How does a symmetrical molecule relate to dipole moment?

  It has no dipole moment
• What do Lewis structures show?

  Atoms bonded and lone-pair electrons

  
• What is formal charge?

  Difference in valence and owned electrons
• How is formal charge calculated?

  Formal charge = valence - half bonding - nonbonding

  
• What is the formal charge of oxygen in water?

  0

  
• What is the formal charge of oxygen in hydroxide ion?

  -1

  
• What does an electrostatic potential map show?

  Charge distributions using color
• What is the valency of carbon?

  4
• What happens if an atom has fewer covalent bonds than its valency?

  It will have negative charge(s)
• What is hydrogen bonding?

  A molecular interaction, not a bond
• What is the directional preference of hydrogen bonding?

  Best when X―H and Y are straight
• What is the shared pair of electrons in O—H bonds closer to?

  Oxygen nucleus than hydrogen nucleus
• How does ice's structure relate to hydrogen bonding?

  Ordered structure due to hydrogen bonding
• What role does the amide group play in hydrogen bonding?

  Both donor and acceptor in bonding
• How do hydrogen bonds affect the shape of peptides?

  They determine the overall shape of molecules
• What holds the two strands of DNA together?

  Hydrogen bonding