3-2-1 WOC : Water 3

– Identify

three

“unique” properties of water.

2

– Describe how the “polar” nature of the water molecule contributes to

two

of the “unique” properties of water you listed.

1

– State

one

environmental impact that results from water being an “universal” solvent.

Hydrogen “bond” – an additional attractive force (dipole-dipole electrostatic attraction) - much weaker than ionic or covalent bonds Usually seen with compounds that contain H covalently bonded to F, O, or N.

Typically, N-H and/or O-H, rarely F-H Represented by ( ….

) Hydrogen bonds can be intermolecular (between molecules) and/or intra-molecular (structural folding, i.e. proteins, DNA…)

 51. Explain the difference between a temporary dipole and a permanent dipole. A temporary dipole forms when one molecule is close to another molecule and the electrons repel each other creating a greater electron density in one part of the molecule.

Permanent dipoles are found in polar molecules in which some regions of the molecule are always partially positive and partially negative.

 52. Why are dispersion forces weaker than dipole-dipole forces?

Dispersion forces are between temporary dipoles. Dipole-dipole forces are between permanent dipoles.

 53. Explain why hydrogen bonds are stronger than most dipole-dipole forces. A hydrogen bond involves a large difference in electronegativity between the hydrogen atom and the atom it is attached to (O,N,F), making the bond extremely polar.

 54. Compare intramolecular and intermolecular forces. Intramolecular forces hold atoms together in a molecule while intermolecular forces hold different molecules together.

 55. Hypothesize why long, nonpolar molecules would interact more strongly with one another than spherical nonpolar molecules of similar composition.

Because long molecules have greater surface areas, more intermolecular forces can exist.

 56. Use relative differences in electronegativity to label the ends of the polar molecules listed as partially positive or partially negative.

 A. HF  B. HBr H – F H – Br δ + δ  C.NO

N – O  D. CO C – O  57. Draw the structure of the dipole-dipole interaction between two molecules of carbon monoxide.

 58. Decide which of the substances listed can form hydrogen bonds.

 A. H2O  B. H2O2  C. HF  D. NH3 All of the substances above can form hydrogen bonds.

 59. Decide which one of the molecules listed below can form intermolecular hydrogen bonds, and then draw it, showing several molecules attached together by hydrogen bonds.  A. NaCl  B. MgCl2  C. H2O2  D. CO2