Polarity of Water

• Hydrogen bond: O- will bond with H+ on a different molecule of H2O

• H2O can form up to 4 bonds

• Oxygen is a more electronegative atom than Hydrogen, and this allows it to attract H+ atoms from different molecules.

• Each O- atom can form two bonds H+ atoms from other molecules and each H+ atom can form one bond with other O- atoms

Properties of Water

1. Cohesion: H-bonding  between like molecules

   1. Surface Tension: measure of how difficult it is to break or stretch surface of liquid

   2. Water is very cohesive because of hydrogen bonding between its molecules, and therefore has a high surface tension.

2. Adhesion: bonding between unlike molecules

   1. Adhesion of H2O to vessel walls counters the pull of gravity

3. Transpiration: movement of H2O up plants

   1. H2O clings to each other by cohesion; cling to xylem tubes by adhesion

   2. H bonds are responsible for water’s property of transpiration

      1. They allow H2O molecules to hold together through cohesion and thus act against the force of gravity to move from the roots of a plant to the leaves through water conducting vessels.

Capillary Action

• Capillary action: the movement of water within porous material due to adhesion, cohesion, and surface tension.

• Because water molecules are cohesive to one another and adhesive to the vessel walls of the plant, as the water in plants is transpired a void/hole/pore will be created and more water from the roots will be drawn upward into the plant because of attractions to the walls of tubes within the stems.

Moderation of Temperature

• Heat: total amount of KE in system

• Temperature: measure intensity of heat due to average KE of molecules

• Water’s high specific heat

  • Change temp less when absorbs/loses heat

  • Large bodies of water absorb and store more heat 🡪 warmer coastal areas

  • Create stable marine/land environment

  • Humans ~65% H2O 🡪 stable temp, resist temp. change

• Evaporative Cooling

  • Evaporative cooling: when a liquid evaporates and the surface left behind cools.

    • This happens because the molecules with the greatest KE evaporate and leave behind the molecules with the smallest KE.

    • This moderates temps in lakes and ponds, and prevents mammals and plants from overheating.

  • Water has high heat of vaporization

  • Molecules with greatest KE leave as gas

  • Stable temp in lakes & ponds

  • Cool plants

  • Human sweat

• Insulation by ice

  • Less dense, floating ice insulates liquid H2O below

  • Life exists under frozen surface (ponds, lakes, oceans)

  • Ice = solid habitat (polar bears

Solvent of Life

• Solution: liquid, homogeneous mixture of 2+ substances

• Solvent: dissolving agent (liquid)

• Solute: dissolved substance

• Water: versatile solvent

• Water is one of the most commonly used solvents

• Though it is not a universal solvent, the polarity of water molecules allows for it to dissolve plenty of solutes because of how polar it is.

• Substances with ionic/polar regions can usually dissolve in water.

• The liquid result of a solvent and solute in a homogenous mixture is a solution.