Properties of Water Polar molecule Hydrogen bonding Surface tension Cohesion and adhesion Universal solvent

POLARITY A molecule that has electrically charged areas. Also called a polar substance or polar compound. Non-polar substances do not have charged ends _ + DURACELL

Polarity of Water Two hydrogen atoms form single covalent bonds with an oxygen atom. Because oxygen is more electronegative, oxygen hangs on to more of the negative charge. This results in the region near the two hydrogen atoms having a partial positive charge. A water molecule is a polar molecule with opposite ends of the molecule with opposite charges.

O H H δ+δ+δ+δ+ δ-δ-

Water has a variety of unusual properties because of attractions between these polar molecules. The slightly negative regions of one molecule are attracted to the slightly positive regions of nearby molecules, forming a hydrogen bond. Each water molecule can form hydrogen bonds with up to four neighbors.

–When water reaches 0 o C, water becomes locked into a crystalline lattice with each molecule hydrogen bonded to the maximum of four partners. –As ice starts to melt, some of the hydrogen bonds break and some water molecules can slip closer together than they can while in the solid state. –Ice is about 10% less dense than water at 4 o C.

Surface tension, a measure of the force necessary to break the surface of a liquid. Water has a greater surface tension than other liquids because hydrogen bonds among surface water molecules resist breaking the surface. Water behaves as if covered by an invisible film. Some animals can stand, walk, or run on water without breaking the surface.

COHESION Because water is a polar molecule, it is attracted to itself. CohesionCohesion – is the attractive force between water molecules. O H H O H H

Water molecules like to stick to each other. COHESION Other substances such as alcohol or oil don’t stick to each other as much.

ADHESION Because water is a polar molecule, it is attracted to other substances. AdhesionAdhesion – occurs when molecules of water are attracted to other substances.

WATER DROPLET WINDSHIELD Adhesion is going on between the windshield and the water droplet.

UNIVERSAL SOLVENT

This is a nickname given to water. Water dissolves LOTS of things. Remember: SOLVENT = the thing doing the dissolving SOLUTE = the thing that dissolves away Other polar covalent molecules and ionic compounds can be dissolved by water. Non-polar covalent molecules DO NOT dissolve in water.

Illustrate a solution of CH 4 dissolved in water. O H H δ+δ+δ+δ+ δ-δ- O H H δ+δ+δ+δ+ δ-δ- O H H δ+δ+ δ+δ+ δ-δ-

Illustrate a solution of LiBr dissolved in water. O H H δ+δ+δ+δ+ δ-δ- O H H δ+δ+δ+δ+ δ-δ- O H H δ+δ+ δ+δ+ δ-δ-