Properties of Water Study Guide

Water has special properties that make life possible, and allow organisms to maintain their temperature and hydration.  Cells count on polar molecules, ions,  to dissolve in water and diffuse into cells.  Would life have begun on Earth without the special properties of WATER.  Students will learn about the importance of hydrogen Bonds.  

The Importance of Water For Life- water has special properties that have allowed life to develop and are critical for the function of organism and their cells.  What we will learn about water.

1.The Hydrogen Bond gives water unique properties

2.Water is the universal solvent

3.Water has a high heat capacity

4.Water has a high heat of vaporization

5.Cohesion and Adhesion

6.Less dense as a solid

THE HYDROGEN BOND

Definition: The weak attraction between water molecules, due to  the slight polar charges on a water molecule.

Because Oxygen is larger, stronger atom. When water is created it makes a covalent bond between two hydrogens and one Oxygen.  Oxygen “hogs” the e+.  In a covalent bond the electron(s) that are shared orbit both bonded atoms.  However in water the e+ spends more time orbiting the far side of the Oxygen atom.  This creates a slight positive end by the hydrogen atoms, because of their proton, and a slight negative end of the molecule, because the electron is mostly hanging out on the Oxygen.

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Hydrogen bonds give water many of it’s special properties. 

The hydrogen bond is strong enough that water molecules stay together, but weak enough that the bond can break and the molecules can flow past each other.

Here water collects above the rim of a glass, it’s hydrogen bonds keeping it from flowing over.

Water is the universal solvent

Water is great at dissolving polar or charged molecules. Uncharged molecules don’t dissolve well in water. It helps get polar molecules into the cell.

Water  has a high heat capacity

Water has a high SPECIFIC HEAT- the amount of energy required to raise the temperature of water by 1°- Hydrogen bonds make it harder to raise the temperature of water. Organisms have a narrow temperature range at which they can live. Organisms are made of large amounts of water. If it was easy to raise the temperature of water, organisms would die.

Water Has A High Heat of Vaporization Threshold

Hydrogen bonds make a higher threshold to go from liquid to vapor. This is important to organisms cooling themselves. Since water with hydrogen bonds holds more heat, you are less likely to dehydrate during physical activity. When it does evaporate from sweat on your skin, it carries away larger amounts of heat.

Cohesion and Adhesion

Cohesion- the property of water being attracted to other water molecules. Because water forms droplets, thousands of organisms can live in a droplet.

Adhesion- Water adheres to other objects due to its polarity. This adherence can create capillary action, and  it helps trees and plants transport water up to the top of tree or plant. Capillary action is, the process of a liquid flowing in a narrow space without the assistance of, or even in opposition to, any external forces like gravity.

SOLID WATER IS LESS DENSE THAN LIQUID WATER DUE TO HYDROGEN BONDS. 

Consider, would life on Earth have developed if solid water was more dense than liquid water?