Properties of Water

Water is the molecule of life. Water has very unique and important properties. O HH

H2OH2O O H H Covalent bonds The bonds holding oxygen and hydrogen atoms together in a water molecule are covalent bonds - - electrons are shared.

H2OH2O O H H In some covalent bonds, electrons are not shared equally.

H2OH2O O H H + + _ Oxygen has a large attraction for electrons, so it pulls electrons toward itself, thus acquiring a negative charge. Hydrogen is weak and loses its electrons to oxygen, thus acquiring a positive charge.

H2OH2O O H H This unequal sharing results in a polar molecule. ++ _ Negative end Positive end

H2OH2O O H H + + _ Water is a polar molecule because it has a negative end and a positive end. Water is polar! Negative end Positive end

_ _ _ _ _ Hydrogen bonds

Water molecules are attracted to each other. This attraction is called a hydrogen bond.

_ _ _ Hydrogen bonds A hydrogen bond is an attraction between a slightly positive hydrogen atom and a slightly negative atom, often oxygen or nitrogen.

Properties Related to Hydrogen Bonds Individual hydrogen bonds are about 20 times weaker than typical chemical bonds, but the additive effect produces a relatively strong force. Chemical Bond --- very strong Hydrogen Bonds --- very weak

Explain: One hydrogen bond is weak, but when you add the attractive forces of all the hydrogen bonds, the overall force is large.

As a result, a large amount of energy is needed to overcome the attractions among water molecules. As a result, water has a relatively high boiling point. C

Why does water have a high boiling point? Liquid water One molecule of water

Explain: In order for water to boil, a water molecule must overcome the forces of attraction (hydrogen bonding) between it and other water molecules. A large amount of energy must be absorb by water in order to have enough energy for the molecule to break away.

Density and States of Matter Solids are more dense than liquids. Liquids are more dense than gases. more denseless dense

What happens when water freezes? It floats. more dense less densesolid liquid

Why? Solid water (ice) is less dense than liquid water. Water is unique!!!

Do ponds freeze solid in winter? Why don’t ponds freeze solid in winter? Because ice is less dense than water! NO!

Hydrogen bonds are responsible for many important properties of water: High specific heat: Water has a high specific heat; this means that water must absorb a great amount of energy to increase its temperature. As a result, water resists changes in temperature; Why is this important?

Water has a high specific heat. Why is this important to the pond?

During the summer, the land and bodies of water receive a large amount of solar radiation. The water in the pond is absorbing a large amount of energy (solar radiation), but the temperature increases a relatively small amount. No harm comes to the fish and other organisms in the water.

Why is water’s high specific heat important to cells? An adult human is composed of approximately 60% water. What are cells composed of? WATER!

Why is water’s high specific heat important to cells? Your body functions best at 98.6 °F, below or above this temperature the body is stressed. At temps of 96 °F or 104 °F, the situation becomes critical. Why?

Most reactions in your body are controlled by enzymes. Enzymes stop functioning at these low (96 °F) and high (104 °F) temperatures. If the enzymes stop functioning, the reactions they control do not occur. Metabolism stops and your cells die.

Cohesion is an attraction between molecules of the same substance. Cohesion makes water molecules stick to each other. This is why water forms beads.

On the space station, Molecules of water stick to each other …. cohesion…. forming a sphere.

Cohesion also produces surface tension, which makes a kind of skin on water, allowing insects to walk on it without sinking.

Adhesion is an attraction between molecules of different substances. Water sticks to other things.

Adhesion is responsible for the upward curve on the surface of the water in a test tube because water molecules are attracted to the glass of the test tube.

In plants, adhesion helps plants transport water from their roots to their leaves.

Water is a polar molecule. Polar molecules have partial charges.

When electrons are shared equally, the result is a nonpolar molecule.

Nonpolar molecules have no charges.

Many Compounds Dissolve in Water Substances/molecules cannot take part in chemical processes inside cells unless they are dissolved in water. Important substances such as glucose, oxygen, and proteins cannot be transported throughout the body unless they are dissolved in blood (composed of 91% water).

Rule: Like dissolve like polar solvents dissolve polar solutes nonpolar solvents dissolve nonpolar solutes.

Molecules like sugar and proteins dissolve in water because they are also polar. Fats and oils are nonpolar. Fats and oils do not dissolve in water.

A solution is a homogeneous mixture. Examples: milk koolaid tea

A solution consists of two parts: solvent solute Solvent --- water Solute --- sugar

Solvent --- the substance that is present in the greater amount and that dissolves another substance. Solute --- the substance that dissolves in the solvent.

solutesolvent solution

Acid Base