1.1 Structure of Water and Hydrogen Bonding

8/8/2019

ENDURING UNDERSTANDING SYI-1 Living systems are organized in a hierarchy of structural levels that interact. 1.1 Structure of Water and Hydrogen Bonding

SYI-1.A Explain how the properties of water that SYI-1.A Explain how the properties of water that result from its polarity and hydrogen bonding affect result from its polarity and hydrogen bonding affect its biological function. its biological function. – Polarity  The hydrogen bonds between water molecules result in • Oxygen more electronegative than hydrogen cohesion, adhesion, and surface tension. • Electrons spend more time closer to Oxygen • Uneven charge on molecule makes it polar. • Polarity creates hydrogen bonds • H-bonds are responsible for emergent properties of water

1 8/8/2019

SYI-1.A Explain how the properties of water that SYI-1.A Explain how the properties of water that result from its polarity and hydrogen bonding affect result from its polarity and hydrogen bonding affect its biological function. its biological function. – Cohesion – Adhesion • Hydrogen bonds hold water molecules • H- bonds hold water molecules to another substance together • Adhesion to solid surfaces creates capillarity • Creates Surface tension • Capillarity allows water to move against gravity – Measurement of the difficulty to break • Plants can grow tall or stretch the surface of a liquid – Must break the H-bonds to break the tension

SYI-1.A Explain how the properties of water that SYI-1.A Explain how the properties of water that result from its polarity and hydrogen bonding affect result from its polarity and hydrogen bonding affect its biological function. its biological function. – High Specific Heat • Amount of heat absorbed or lost – Heat of Fusion to change temperature by 1oC • Quantity of heat required to convert unit mass of a liquid into a solid • Water’s high specific heat is due • Temp of surrounding rises to H-bonds • Keeps temperatures constant • Creates evaporative cooling • Regulates temp in standing bodies of water • Prevents overheating • Temp of surrounding drops

SYI-1.A Explain how the properties of water that SYI-1.A Explain how the properties of water that result from its polarity and hydrogen bonding affect result from its polarity and hydrogen bonding affect its biological function. its biological function. – Density - Versatile Solvent • Less dense as solid than liquid • Breaks up ionic compounds • Due to hydrogen bonding • Dissolves other polar Water molecules • Crystalline lattice keeps Ice molecules at a distance • Creates hydrophylic and hydrophobic interactions • Water is most dense at 4oC= ice floats with different molecules • Keeps free water on earth

2 8/8/2019

SYI-1.A Explain how the properties of water that result from its polarity and hydrogen bonding affect its biological function. – Acid/Base & pH • Water dissociates into a hydrogen ion (hydronium ion) and a hydroxide ion 1. Acids release H + ions 2. Bases release OH- ions • pH Scale 1. “power/percent of hydrogen” 2. measures H+ concentration 3. Each step is a 10x increase • Buffers 1. Substances that accepts or donates H+ ions 2. Minimize change in pH • Acid Rain 1. Causes deforestation by changing soil pH 2. Destroys life in water