Structure of Water & Hydrogen Bonding

Describe the physical and chemical properties of water

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Explain how the properties of water result from its polarity and hydrogen bonding affect its biological function.

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Open Ended

Why is water important?

Water is the single most abundant molecule inside cells.

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It is important to understand how the properties of water interacts and influences other molecules.

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​Water = Life

The bonds of water are polar because oxygen is more electronegative than hydrogen.

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A single water molecules is held together by two covalent bonds, but the slight positivity of the hydrogen atoms attract other water molecules and a hydrogen bond forms between an oxygen and hydrogen molecule.

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Negative bonding to positive = weak hydrogen bond.​

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Life depends on the properties of water.

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Cohesion: water molecules stick to each other.

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Adhesion: Water molecules stick to other things.

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Cohesion creates surface tension.​

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Cohesion, Adhesion & Surface Tension

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Open Ended

Explain how cohesion leads to surface tension and not adhesion.

Surface tension is the measure of difficulty of breaking the surface of a liquid.

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Water has the highest surface tension of common liquids.​ Water's strong tension allows objects to float like leaves to float on top.

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Animals such as the water strider "walk on water" because of it's high surface tension.​

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Surface Tension

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Hydrogen bonding accounts for the 3 states of water.

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Ice - a solid state has many Hydrogen bonds creating a crystal structure.

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Water - a liquid state with a lot of hydrogen bonds, but less than ice. The water molecules continuously make and break hydrogen bonds.

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Water Vapor - a gas ​molecules move too rapidly preventing most hydrogen bonding.

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​Structure of Water

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Open Ended

Why is water important to the life of organisms?

Water is an environment in which the molecules of cells interact and undergo chemical reactions.

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The chemistry of water and how it interacts with ions and molecules are critical to the health and function of a cell.​

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Water is the medium of life

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Cells and organisms are mostly water, ~70%, and live in an aqueous environment.

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Water is a good solvent​ (dissolver) for polar or charges molecules (hydrophilic)

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Nonpolar molecules​ (hydrophobic) have few positive or negative charges and will mostly avoid water.

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​Solvent properties of water.

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Open Ended

Consider what we know about water and hydrogen bonding. Why is water a good solvent?

The O and H molecules in water can dissociate into two molecules. OH^- (hydroxide) and H⁺. This happens when Oxygen takes an electron from one Hydrogen.

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The presence of OH^- and H⁺ affects how water interacts with other ions and molecules.

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Acids donate H⁺ ions and Bases (Alkaline) accept H⁺.​

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Water dissociation and pH

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When water is removed from two or more molecules, it allows a new covalent bond to form between them, forming a new molecule, or adding a new subunit to an existing molecule.

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Dehydration synthesis builds molecules.

Hydrolysis reactions break the covalent bonds by adding water across the bond.

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Hydrolysis means to break using water.

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Hydrolysis is the reverse reaction of dehydration synthesis. ​

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​Hydrolysis reactions break larger molecules down.

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Multiple Choice

Which reaction will create a macromolecule?

• Dehydration Synthesis

• Hydrolysis

Open Ended

Explain 3 properties of water