The Properties of Water That Make Life on Earth Possible Copyright Amy Brown – Science Stuff

What do these pictures have in common? WATER!!!!

Water is the most common ______ on earth. ____ of the surface of the earth is covered in water. liquid ¾’s All living things need water to __________ The unique _______________ of the water molecule determines its unique properties. structure survive

Structure of Water 1 oxygen Water is composed of ___ _______ atom and _____ ____________ atoms. The oxygen has a ____________ charge and the hydrogen has a _______________ charge. When the two hydrogen atoms bond with the oxygen, they ____________ to the ________ of the molecule like _______________ ears. This molecular structure gives water molecules ________, or a lopsided electrical charge that ________ others. 1 oxygen 2 hydrogen negative positive Draw the structure of water attach top Mickey Mouse polarity attracts

a chemical bond formed as a result of the sharing of electrons. Covalent Bonds A covalent bond is: a chemical bond formed as a result of the sharing of electrons. How many covalent bonds does water have? The shared electron moves between: -the nucleus of one atom -to the nucleus of another atom

Polar Covalent Bonds   Electrons are shared unequally resulting in a molecule that has poles. Part of the molecule is negative and part of it is positive. The oxygen is more negative because it has more electrons What else has a positive and negative end?

The above molecule contains ____________ bonds. − − Highly electronegative atom Where the electrons spend the most time will have a slightly negative charge Where the electrons spend the least time will have a slightly positive charge. + + Sharing half of a sweater The above molecule contains ____________ bonds.   polar covalent

NonPolar Covalent Bonds The electrons are shared ______. These bonds exist between: identical atoms such as H2, Cl2, O2, and N2. equally 2 person sweater

− − + + Water and the Hydrogen Bond Each water molecule is made up of two atoms of hydrogen and one atom of oxygen. The hydrogen atoms are linked to the oxygen by a _________ bond. covalent − − Water is neutral in charge since it has the same number of protons as electrons. It is, however, ______. Why is it polar??? oxygen hydrogen hydrogen Because oxygen is greedy and pulling the electrons (sweaters) away from the hydrogens but not hard enough to take them completely away like an ionic bond polar + +

This force of attraction forms: Water and the Hydrogen Bond Water molecules tend to _____________ because water molecules are polar. The ________ end of one water molecule is attracted to the ________ end of another. stick together positive negative This force of attraction forms: hydrogen bonds. Attraction of opposite charges

Hydrogen Bond: A weak molecular bond formed between the hydrogen atom of one molecule to a highly electronegative atom of another molecule. 1 A weak attraction is formed between the hydrogen atom of one molecule and a highly electronegative atom in a different molecule. 4 2 3 Each water molecule can form hydrogen bonds to a maximum of four neighbors.

Check for Understanding #1 What is the difference between polar and non-polar covalent bonds? A polar covalent bond does not share the electrons in the atom equally whereas a non-polar covalent bond does share the electrons equally. Polar example: water Non-polar example: oil, oxygen gas

1. Water is cohesive and adhesive. Water has four properties that contribute to Earth's ability to sustain such abundant life: 1. Water is cohesive and adhesive. 2. Water has the ability to stabilize temperatures. 3. Water expands when frozen. 4. Water is a versatile and universal solvent.

Organisms depend on the cohesion and adhesion of water molecules. Hydrogen bonds form, break, and re-form with great frequency. Each hydrogen bond lasts only a few trillionths of a second. Cohesion: The attraction between like molecules Adhesion: The attraction between unlike molecules. What bond allows water to connect with other molecules?

Ways to remember Cohesion Cohesion and Adhesion! Specifically it’s called Capillary Action Surface Tension video Co= ________ “hesion”= _____ together stick What does Cohesion result in? _______________: A measure of how difficult it is to break the surface of liquid. Example: This allows __________ and small animals to ______ on water. Surface tension insects walk

What is Adhesion? Attraction other plant Adhesion is the _____________ of water molecules to _______ substances like glass, cotton, ________ tissues, soil, etc. Adhesion is important because it allows water to travel ____________ → _________ Action Attraction other plant against gravity Capillary How would water travel against gravity in a plant?

Water moderates temperatures on Earth. Water _________ air temperatures by: - _________ heat from air that is warmer - _________ the stored heat to air that is cooler. Water is a very good "heat bank" It can -absorb or release a large amount of heat -with slight change in its own temperature. stabilizes absorbing releasing

Water stabilizes temperatures because it has a high specific heat. High Specific Heat: absorb or release lots of heat with a slight change in its own temperature.

….changing in its temperature Specific heat can be thought of as a measure of how well a substance resists…. ….changing in its temperature Water has a very HIGH specific heat compared to other substances.

Check for Understanding #2 What does it mean to have a LOW specific heat? Temperature changes can happen instantaneously. Water does NOT have a low specific heat. It has a high specific heat.

Why is this important for life on earth? 1. Life could not exist in bodies of water if there were ______________ in temperature. drastic changes 2. Temperatures on _____ are stabilized by ______________. Large bodies of water ___________ from the sun during the day, _______ landmasses. Large bodies of water ____________ at night, ________ the landmasses. This stabilizes temperatures on land as well as in the water. 3. Because water has such a high specific heat, it keeps water ______ at a wide range of ____________. Why would we want that? land bodies of water absorb heat cooling release heat warming liquid temperatures

What is density? Density is “___________ _________” a substance is. It is how much mass is contained in a given volume. Objects with __________ density will ________ tightly packed higher sink lower float

Oceans and lakes do not freeze solid because ice floats. Water is _________ as a solid than it is as a liquid. In other words, ________. Water expands as it solidifies, making it less dense. less dense ice floats Oceans and lakes do not freeze solid because ice floats. The floating ice _________ the liquid water below, preventing it from _______ and allowing life to exist ______ the frozen surface. insulates Krill under the ice. freezing under

Is Ice less dense than water? Yes, ice is less dense than water. Because hydrogen bonding creates _______ space between water molecules so they __________. more spread out

Why is it rare that the oceans freeze? The water in the world’s oceans is _________. Salt __________ the ____________ temperature of water. salty lowers freezing

Water is the solvent of life. Solution: A homogeneous mixture of the molecules of two or more substances Water is the solvent of life. Solvent: The part of a solution that does the dissolving. Solute: The part of the solution that gets dissolved.

Water makes an excellent _______ because the _____ water molecules tend to separate _____ compounds into their components. JUST LIKE MAGNETS! solvent polar ionic Example: H2O + NaCl  H2O + Na+ + Cl- Water Ionic Salt Water Broken Ionic Compound Water will dissolve ______________, but not _________ substances such as ___________. Like dissolves like: Water is polar so it must dissolve polar or charged substances. polar molecules nonpolar A substance does not have to be ionic as in the above example to be dissolved by water, but it does have to be polar. Example: Sugar is not ionic but is polar, and therefore will dissolve in water. fats and oils

Hydrophilic Hydrophobic Hydrophilic means “____________”. Will they dissolve in water? Hint: Hydrophilic molecules are polar or ionic compounds. water-loving Hydrophilic Hydrophobic Hydrophobic means “____________”. Will they dissolve in water? Hint: Hydrophobic molecules are nonpolar compounds. water-fearing

Check for Understanding #3 What causes water to be a universal solvent? Because water is a polar covalent molecule, it wants to bond with other substances causing them to dissolve. They act like magnets.

When a charged molecule is dissolved in water, it may change the number of ___________ions.   Example: Hydrochloric Acid dissolved in water HCl + H2O  H+ + Cl- This solution contains more ___ ions than ____ ions.  Example: Sodium Hydroxide dissolved in water NaOH + H2O  Na+ + OH- This solution contains more ____ ions than ____ ions. Acidic solution: The number of H+ ions exceeds the number of OH- ions. Basic solution: The number of OH- ions exceeds the number of H+ ions. H+ and OH- H+ OH- OH- H+

The pH Scale The pH scale is a scale used to describe how _____________ a substance is. The pH scale ranges from _______.   pH of 7 = _______. The concentrations of H+ ions and OH- ions are _______________. pH below 7 = ______. The concentration of H+ ions is _______ than OH- ions. pH above 7 = _____. The concentration of OH- ions is ________than H+ ions. acidic or basic 1 to 14 neutral exactly the same acidic greater basic greater

Living organisms try to maintain…. …. homeostasis or a balance. Living organisms do not want to get ___________________ because the _________________ of the cell will stop. The pH of most living cells is close to 7. This must be maintained or the cell may die. too acidic or too basic chemical processes

Check for Understanding #4 And why is it important to have a balance of H+ and OH- ions? Balance is important because our bodies need to maintain homeostasis (remain constant) so that we can function in our day-to-day life.

TO THE OLYMPICS! OF WATER!