STRUCTURE & PROPERTIES OF WATER

One of very few compounds that is liquid at temperatures found on earth’s surface. One of very few compounds that is liquid at temperatures found on earth’s surface. Covers more than 75% of earth’s surface. Covers more than 75% of earth’s surface. Most abundant compound in nearly all living organisms. Most abundant compound in nearly all living organisms. Expands as it makes phase change from liquid to solid. Expands as it makes phase change from liquid to solid.

Covers 3/4 th of earth’s surface Covers 3/4 th of earth’s surface Earth known as “blue planet” Earth known as “blue planet” 97% salt water i.e. oceans 97% salt water i.e. oceans 3% fresh water i.e. lakes, streams, rivers, glaciers, soil, atmosphere, biomass 3% fresh water i.e. lakes, streams, rivers, glaciers, soil, atmosphere, biomass 3 forms (solid, liquid, gas) 3 forms (solid, liquid, gas) Water Cycle: “hydrologic cycle”: Unending circulation process powered by the sun Water Cycle: “hydrologic cycle”: Unending circulation process powered by the sun

HOW SALTY IS THE OCEAN?... If the salt in the sea could be removed and spread evenly over the Earth's land surface it would form a layer more than 500 feet thick If the salt in the sea could be removed and spread evenly over the Earth's land surface it would form a layer more than 500 feet thick … about the height of a 40-story building

Ice caps and glaciers 79 % Groundwater 20% Other fresh water 1 % Freshwater

Other Fresh Water Lakes 52% Soil Moisture 38 % Water in organisms 1% Rivers 1% Atmosphere 8%

Structure of Water The polarity of water: Water has a simple molecular structure. Each hydrogen atom is covalently bonded to the oxygen via a shared pair of electrons. Oxygen is an "electronegative" or electron "loving" atom compared with hydrogen. The polarity of water: Water has a simple molecular structure. Each hydrogen atom is covalently bonded to the oxygen via a shared pair of electrons. Oxygen is an "electronegative" or electron "loving" atom compared with hydrogen.

Water is a "polar" molecule, meaning that there is an uneven distribution of electron density. Water has a partial negative charge near the oxygen atom due the unshared pairs of electrons, and partial positive charges near the hydrogen atoms. Water is a "polar" molecule, meaning that there is an uneven distribution of electron density. Water has a partial negative charge near the oxygen atom due the unshared pairs of electrons, and partial positive charges near the hydrogen atoms.

Polarity of Water

HYDROGEN BONDING: The fact that the oxygen end of a water molecule is negatively charged and the hydrogen end positively charged means that the hydrogen's of one water molecule attract the oxygen of its neighbor and vice versa. This is because unlike charges attract. The fact that the oxygen end of a water molecule is negatively charged and the hydrogen end positively charged means that the hydrogen's of one water molecule attract the oxygen of its neighbor and vice versa. This is because unlike charges attract.

Fig 3.2 Hydrogen bonding between water molecules

Ionic compounds & polar molecules dissolve in water Ionic compounds: Ions Ionic compounds: Ions attracted to ends of water molecules with opposite charge. Ending solution is a Ending solution is a mixture of ions and water molecules. Both cases, ions or Both cases, ions or molecules are evenly distributed in water.

Nonpolar molecules do not dissolve well in water Nonpolar molecules Nonpolar molecules do not dissolve in do not dissolve in polar molecules. polar molecules. i.e. Oil and Vinegar i.e. Oil and Vinegar

Water is the solvent of life

Water is called the "universal solvent" because it dissolves more substances than any other liquid. This means that wherever water goes, either through the ground or through our bodies, it takes along valuable chemicals, minerals, and nutrients. Water is called the "universal solvent" because it dissolves more substances than any other liquid. This means that wherever water goes, either through the ground or through our bodies, it takes along valuable chemicals, minerals, and nutrients. Difference b/w solute and solvent? Difference b/w solute and solvent?

Adhesion and Cohesion Water is attracted to other water. This is called cohesion (attraction of substances of same kind) Water can also be attracted to other materials. This is called adhesion (attraction b/w different substances)

Cohesion and Surface Tension The cohesive forces between molecules down into a liquid are shared with all neighboring atoms. Those on the surface have no neighboring atoms above, and exhibit stronger attractive forces upon their nearest neighbors on the surface. This enhancement of the intermolecular attractive forces at the surface is called surface tension. The cohesive forces between molecules down into a liquid are shared with all neighboring atoms. Those on the surface have no neighboring atoms above, and exhibit stronger attractive forces upon their nearest neighbors on the surface. This enhancement of the intermolecular attractive forces at the surface is called surface tension.cohesive forcessurface tensioncohesive forcessurface tension

Cohesion of water leads to surface tension Cohesion of water leads to surface tension SURFACE TENSION: The force necessary to stretch or break the surface of a liquid. * Greater in water than in most liquids. Walking on water Small insects can walk on water because their weight is not enough to penetrate the surface.

Surface tension is the name we give to the cohesion of water molecules at the surface of a body of water.

Capillary Action Movement of water w/in the spaces of a porous material due to the forces of adhesion, cohesion and surface tension. Movement of water w/in the spaces of a porous material due to the forces of adhesion, cohesion and surface tension. Paper towel demonstration i.e. Water & dissolved substances move through roots of plants. i.e. Moves through tiny blood vessels in our body.

Fig 3.5 Expansion upon freezing Water is less dense as a solid than a liquid.

Ice insulates the water below Ice is about 10% less dense than water at 4 degrees Celsius, therefore it floats.

Think Critically… When salt is added to water, the freezing point of water decreases. Explain why this occurs.

What do the following ALL have in common?

List substances that you encounter in a typical day. Separate substances into one of two categories: Acids or Bases List substances that you encounter in a typical day. Separate substances into one of two categories: Acids or Bases

H 2 O  H + + OH - Hydrogen ion hydroxide ion Pure Water has a low concentration of H+ & OH- which are present in equal numbers. Pure Water has a low concentration of H+ & OH- which are present in equal numbers.

Acid: Compounds that form hydrogen ions when dissolved in water. (Proton donors) Strong Acid: Ionizes/Dissociates (Breaks apart) completely in a solvent Weak Acid: Releases few hydrogen ions in aqueous (water) solution.

Characteristic of Acids Release hydrogen ions in solution Release hydrogen ions in solution Corrode active metals (reactivity w/metals) Corrode active metals (reactivity w/metals) Taste sour Taste sour Turn Litmus Paper red Turn Litmus Paper red

Bases: (Alkali) Compounds that produce hydroxide ions (OH-) when dissolved in water. (Proton acceptors) Strong Bases: Completely ionizes in a solvent. Weak Bases: Releases few hydroxide ions in aqueous solution.

Characteristics of Bases Release hydroxide ion in water Release hydroxide ion in water Bitter Taste Bitter Taste Feel slippery Feel slippery Changes litmus paper blue Changes litmus paper blue

Both Acids and Bases are Electrolytes Electrolyte: Allows the flow of an electric current Strong: Completely dissociate Weak: Provide few ions in solution (Ionic compounds generally strong electrolytes)