The Water Molecule: Covalent Bonding
2.2 The Properties of Water
The Water Molecule The Chemical formula for Water is H2O Overall, Water is Neutral, because it has same amount of protons (+) as it does electrons (-). The breakdown: Oxygen has: 8 (+) and 8 (-) 2x Hydrogen has: 2 (+) and 2 (-) Total: 10 (+) 10(-) NEUTRAL!
...HOWEVER, There’s more to H2O With 8 protons, water’s Oxygen atom has a stronger pull on the electrons in the molecule than the single protons found in each Hydrogen atom.
THE RESULT: electrons spend more time around the oxygen atom than the 2 hydrogen atoms. Therefore, water has a partial negative charge at one end, and a partial positive charge on the other. Due to this “uneven sharing” of electrons, the water molecule is said to be POLAR. Water molecules are partially negative by the Oxygen atom. Water molecules are partially positive by the 2 Hydrogen atoms.
Because of their partial positive and negative charges, polar molecules such as water can attract each other. The attraction between a hydrogen atom with a partial positive charge and another atom with a partial negative charge is known as a Hydrogen Bond.
Hydrogen Bonds
Hydrogen Bonds
Water is a Universal Solvent Because water is a polar molecule, it is able to form multiple hydrogen bonds, which account for these special water properties: Cohesion and Adhesion Less Dense as a Solid High Heat Capacity Water is a Universal Solvent
Cohesion vs. Adhesion
Cohesion – an attraction between molecules of the same substance. Water on Wax paper
Adhesion – an attraction between molecules of different substances Adhesion – an attraction between molecules of different substances. Water on a Glass surface
Another Picture…
Water is less dense as a Solid
Water is less dense as a Solid What does this mean? ICE FLOATS!
Water has a High Heat Capacity Or simply, Water can hold onto lots of Heat Energy This is important for a few reasons... 1. Oceans temps stay relatively stable for aquatic life. 2. A Cell’s activity generates lots of heat, heat that is readily absorbed and managed by WATER.
1. Solutions 2. Suspensions Rarely does Water exist in its pure form It is typically part of a Mixture. There are 2 main types of mixtures: 1. Solutions 2. Suspensions
Water is known as a Universal Solvent Solutions – type of mixture in which all components are evenly distributed. There are 2 parts to any solution 1. Solvent – substance that does the dissolving. 2. Solute – substance that is dissolved in a solution Water is known as a Universal Solvent
Salt Dissolved in Water
A solute dissolves in the solvent. Solutions continued Example – When Table Salt (the solute), is placed in water (the solvent), the water dissolves it. A solute dissolves in the solvent.
Suspension
Water keeps things suspended. 2. Suspensions – type of mixture in which the particles are nondissolved and stay suspended in the liquid or gas. Water keeps things suspended.
Acids, Bases and pH H2O H+ + OH- One water molecule in 550 million naturally dissociates into a Hydrogen Ion (H+) and a Hydroxide Ion (OH-) Hydrogen Ion Hydroxide Ion Acid Base H2O H+ + OH-
Acids, Bases, and pH The separation of water molecules into ions causes solutions to be acidic, basic, or neutral. H2O H+ and OH- The pH scale measures how acidic or basic a solution is. pH of 7—Neutral: Equal concentrations of H+ and OH- pH below 7—Acidic: Relatively high concentration of H+ pH above 7—Basic: Relatively high concentration of OH-
The pH Scale Indicates the concentration of H+ ions Ranges from 0 – 14 pH of 7 is neutral pH 0 up to 7 is acid … H+ pH above 7 – 14 is basic… OH- Each pH unit represents a factor of 10X change in concentration pH 3 is 10 x 10 x 10 (1000) stronger than a pH of 6
Acids Strong Acids have a pH of 1-3 Produce lots of H+ ions
Bases Strong Bases have a pH of 11 to 14 Contain lots of OH- ions ewer H+ ions
Buffers Weak acids or bases that react with strong acids or bases to prevent sharp, sudden changes in pH (neutralization). Produced naturally by the body to maintain homeostasis Weak Acid Weak Base