Two hydrogen atoms, each with one proton, share two electrons in a single nonpolar covalent bond. Fig. 2.8, p.27 Chemical Bonding Review

Two oxygen atoms, each with eight protons, share four electrons in a nonpolar double covalent bond. Chemical Bonding Review Fig. 2.8, p.27

Oxygen has vacancies for two electrons in its highest energy level orbitals. Two hydrogen atoms can each share an electron with an oxygen. The resulting two polar covalent bonds form a water molecule. What is wrong with this model of the water molecule? Chemical Bonding Review Fig. 2.8, p.27

Water’s polar nature results in a charge attraction between the hydrogens of one water molecule and the oxygen of another. Fig. 2.9, p.27 Water molecules are bent, resulting in a lopsided placement of electrons. Thus, water molecules are polar. CH 2.5

Two molecules interacting weakly in one H bond, which can form and break easily H bonds helping to hold part of two large molecules together. Many H bonds hold DNA’s two strands together along their length. Individually they are weak, but collectively stabilize DNA’s large structure. Fig. 2.9, p.27 Hydrogen Bonds

The Water Molecule is polar, but some things are not polar. Oil has no charges, is nonpolar and therefore hydrophobic Salt is ionic, has charges like water, and is therefore hydrophilic

Water’s polarity allows it to operate as a UNIVERSAL SOLVENT.

How does this allow for life to exist? Water’s Emergent Properties Universal Solvent Negative oxygen regions of polar water molecules are attracted to sodium cations (Na + ) Cl – – – – – Na + Positive hydrogen regions of water molecules cling to chloride anions (Cl – ) – – – – – – Na + Cl –

Many “salt” ions are important components of cellular processes. Sodium, Potassium, and Calcium are essential for muscle and nerve function.

Water can also interact with polar molecules such as proteins.

Water molecules “stick” to each other, but while the molecules of water are attracted to each other, they can FLOW past each other while in their liquid state. Water’s Emergent Properties Cohesion and Adhesion Fig. 2.12, p.29 Fig. 2.10, p.28

How does this allow for life to exist? Water’s Emergent Properties Cohesion and Adhesion Fig. 2.12, p.29 Fig. 2.10, p.28

The attractive forces between water molecules and nonwater surfaces give water the property called ADHESION. Water’s Emergent Properties Cohesion and Adhesion

Cohesion and adhesion work together to produce the phenomenon of Evapotranspiration. Water conducting cells 100 µ m

Cohesion and adhesion also work together to produce the phenomenon of Surface Tension. Water’s Emergent Properties Cohesion and Adhesion

EVAPOTRANSPIRATION is a significant part of the Water Cycle.

Water has a high Specific Heat, which leads to a temperature stabilizing effect. Water’s Emergent Properties Moderation of Temperature

How have some animals evolved to employ water’s high specific heat and therefore high Heat of Vaporization? Water’s Emergent Properties Moderation of Temperature Heat of Vaporization

Water’s high Specific Heat helps give the earth a narrow temperature range from day to night and season to season. Water’s Emergent Properties Moderation of Temperature

The high specific heat gives water a high Heat of Vaporization which leads to Evaporative Cooling. Water’s Emergent Properties Moderation of Temperature

As water cools and the molecules slow down, the hydrogen bonds become more established and the water molecules more organized. Therefore, ice is less dense than liquid water. Water’s Emergent Properties The Density Anomaly

How does this allow for life to exist? Water’s Emergent Properties The Density Anomaly

There is life under ice in the winter.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Acids and Bases An acid –Any substance that increases the hydrogen ion concentration of a solution. A base –Any substance that reduces the hydrogen ion concentration of a solution (with respect to hydroxide ions). CH 2.6

Fig. 2.13, p.30 Water naturally has a small concentration of hydrogen ions and hydroxide ions in solution. Acids release (or donate) hydrogen ions when dissolved in water and can increase the concentration of hydrogen ions, thus lowering the pH. pH

Lemons and other citrus fruits are high in citric acid and thus have a low pH. pH

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings How Does the pH Scale Work? In pure H 2 O, there are always 1 X M of H + ions and 1 X M of OH - ions. The product of these two concentrations is a constant (K w ), and at 25ºC is: X =

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings How Does the pH Scale Work? The pH of a solution is determined by the relative concentration of hydrogen ions.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings How Does the pH Scale Work? The pH of a solution is calculated using the equation: pH = -log [H + ] (all at 25ºC). pH

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The pH Scale Therefore, the pH of a solution is determined by the relative concentration of hydrogen ions. –pH is low in an acid. –pH is high in a base.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Buffer Systems: How nature buffers itself against changes in pH The internal pH of most living cells must remain close to pH 7. Buffer Systems –Are substances that minimize changes in the concentrations of hydrogen and hydroxide ions in a solution –Consist of an acid-base pair that reversibly combines with hydrogen ions

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Buffer Systems: How nature buffers itself against changes in pH The Blood Buffer System –Carbon dioxide in blood dissolves in the water in blood to form carbonic acid. –One of the hydrogens of each carbonic acid molecule dissociates to the hydrogen ion, keeping the blood from being too alkaline and helping maintain a blood pH of 7.4. –Any excess hydrogen ions are swept up by the bicarbonate ion and any excess hydroxide ions are swept up by the hydrogen ion. In Blood

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Red Blood cells bind H + ions from H 2 CO 3 – This leaves more HCO 3 - ions in the blood plasma than H + ions The lungs can remove excess CO 2 from the blood. The kidneys can remove excess HCO 3 - ions from the blood. CO 2 Buffer Systems and Maintaining Homeostasis of pH

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Acidosis and Alkalosis

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Acidosis and Alkalosis

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Acidosis and Alkalosis

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Threat of Acid Precipitation - Linking Acid to Ecology Acid precipitation refers to rain, snow, or fog with a pH lower than pH 5.6, and is caused primarily by the mixing of different pollutants with water in the air.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Threat of Acid Precipitation - Linking Acid to Ecology Aquatic ecosystems differ in their ability to buffer against pH changes from sources like acid rain. Oligotrophic LakeEutrophic Lake