The chemical reactions of all living things take place in an aqueous (water based) environment. Thus, water is one of the most important compounds found in living things! Properties of Water Chapter 2 Revised Jul 2014

Roughly 70 percent of an adult’s body is made up of water. By the time a person feels thirsty, his or her body has lost over 1 percent of its total water amount. Although a person can live without food for more than a month, a person can only live without water for approximately one week. Your brain is 75-85% water and plays a vital role in your body's response to dehydration. It controls water intake through altering thirst and varying the water excretion from your kidneys. http://www.healthy-water-best-filters.com/human-water-cycle.html Water Fun Facts http://fiteats.wordpress.com/page/3/ http://science.howstuffworks.com/environmental/earth/geophysics/h2o3.htm http://www.mpip-mainz.mpg.de/documents/akbu/pages/ssci.html

B. Chemical formula = H20 --2 parts hydrogen --1 part oxygen A. Water is the single most abundant compound in most living things B. Chemical formula = H20 --2 parts hydrogen --1 part oxygen 8P 8N 1P 0N Bohr Model for water (covalent bonds)

D. Water compound is a POLAR covalent 1. Polar = the electrons are unevenly shared between the hydrogen and oxygen atoms. 2. Oxygen pulls on the e- greater than the H . . .so at any moment, the shared e- are more likely closer to the oxygen

Structure of Water: Polarity Polarity: electrons are not shared equally. Causes the oxygen to be negatively charged and the hydrogens to be positively charged. (–) (+) O H

3. What effect does “polar” have? --water has a partial pos. pole and partial neg. pole --like a magnet

E. Hydrogen Bonding 1. The partial + and partial – charges allow H2O molecules to attract to each other or stick together through Hydrogen Bonds 2. Hydrogen bonds are WEAK bonds that can be easily broken 3. H-bonds = responsible for H20 special properties . . .

Hydrogen Bonds Hydrogen Bond: (–) (+) O H Hydrogen Bonds Hydrogen Bond: Weak attractive force between a negatively charged hydrogen and a positively charged atom (on a different molecule.)

F. PROPERTIES OF WATER: 1. Strong cohesion and adhesion forces!

Cohesion= attraction between molecules of the SAME substance Explains why water beads up

. . . Due to the hydrogen bonding of surface molecules to each other Example 2: Cohesion leads to water having a high surface tension . . . Due to the hydrogen bonding of surface molecules to each other Images from: http://understanding-biology.blogspot.com/2010/01/floating-paper-clip-cohesion-surface.html

b. Adhesion = attraction between molecules of DIFFERENT substances Explains why microscope slides stuck together

capillary action in plants Example of both cohesion and adhesion of water working together . . . capillary action in plants

TedEd video clip on water

2. Ability to absorb heat: Water can absorb large amounts of thermal energy before its own temperature begins to rise. Water acts like a heat buffer for the globe.

3. Ice is less dense than liquid water Image from: http://www.wallpaperbase.com/landscape-iceberg.shtml

4. Ability to form solutions Water is VERY EFFECTIVE in dissolving many other substances “Universal solvent”

Water is the ‘universal solvent’ Solution = liquid consisting of uniform mixture of two or more substances Two parts of a solution: Solvent = liquid (dissolving agent) Solute = substance dissolved EXAMPLE: Water = solvent Koolaid powder/sugar = solutes Kool-aid = solution

Remember the rule to make a solution: “Like dissolves like.” Since water is polar, it will dissolve ions and other polar substances (like salt!) Na+ Cl- Hydrophilic = Water Lover Water will NOT dissolve nonpolar substances

Non polar molecules are hydrophobic Electrons are shared equally in nonpolar molecules. Oil is an example of a nonpolar molecule. It does not form hydrogen bonds. Like dissolves like, therefore, oil (nonpolar) does not mix with water (polar). Nonpolar molecules are hydrophobic (“afraid of water”) because they do not mix with water.

Properties of Water—seen in space

Simulation: Overview of water properties Simulation found at: http://www.sumanasinc.com/webcontent/animations/content/propertiesofwater/water.html

surface tension= A measure of how difficult it is to stretch or break the surface of a liquid. Water has a high surface tension because of the hydrogen bonding of surface molecules Electronegativity=The attraction of an atom for the electrons of a covalent bond Electronegativity is the tendency for an atom to pull electrons toward itself. Two atoms of the same element have equal electronegativities; in a covalent bond they share electrons equally, forming a nonpolar covalent bond.