Chapter 2 - WATER “Humans are essentially made up of 5 gallons of water and $100 worth of assorted chemicals” - Anonymous Scientist

Water is the Cradle of Life Why Water? A) Water has a simple atomic structure 1.Contains oxygen bound to two hydrogens by covalent bonds B) Water is Polar 1. The greater electronegativity of OXYGEN makes water polar 2. Electronegative atoms attract electrons away from other atoms – these electronegative atoms are negatively charged 3. Water carries two partial charges due to electronegative oxygen 4. Hydrogens carry slight positive charges; oxygen carries a slight negative charge

C) Polar molecules and hydrogen bonding 1 C) Polar molecules and hydrogen bonding 1. Due to slight charges, weak interactions between atoms from 2. Hydrogen Bonds: weak transient (temporary) attractions between and electronegative atom and hydrogen 3. Cumulative effect of hydrogen bonds is the responsible for the many properties of water.

Living systems depend on properties of water that result from its polarity and hydrogen bonding. Polarity and hydrogen bonding contribute to the following properties of water : Cohesion Adhesion High specific heat capacity Universal solvent supports reactions Heat of vaporization Heat of fusion Water’s thermal conductivity

Water Kit Activity Please make the following chart in your notebook. Leave ample room to write. QUESTION ANSWER What Holds Water Molecules Together? How Does Water Go Up Plants? How Does Salt Dissolve in Water? How Does Water Boil? How Does Water Freeze? Why will Oily Substances Not Dissolve in Water Why Does Ice Float? Sugar Has Many Carbons; Why Does it Dissolve in Water? Why Does Water Form Droplets on an Apple? Why is Water a Liquid?

Questions: What is transpiration? Explain how adhesion and cohesion affect transpiration in plants. Why do we sweat to cool off? Why does the ocean temperature reach peak temperatures in September – after summer? Why don’t oil and water mix?

Relative Acidity – pH pH is a measure of the concentration of hydrogen ions in a solution pH is maintained by BUFFERS Buffer – compound that maintains a constant pH Bicarbonate ion is a buffer that can add or remove hydrogen ions from solutions (blood plasma)