Chapter 3 - Water

• Water is a polar molecule and because of its polarity, it may create hydrogen bonds.   * These hydrogen bondings provide water with qualities that are necessary for life on Earth.
• Covalent bonds (shared electrons) exist between the oxygen and hydrogen atoms in water.   * %%Oxygen has a high electronegativity (ability to attract electrons), whereas hydrogen has a low electronegativity.%%   * Because of this difference in electronegativity, electrons in the covalent link between oxygen and hydrogen are unequally shared, with electrons spending more time around the oxygen atom.   * As a result, a polar covalent bond is formed with a partial negative charge around the oxygen atom and a partial positive charge around the hydrogen atom, as seen in the image attached.   * As a result, the partial negative charge on an oxygen atom in one water molecule attracts the partial positive charge on a hydrogen atom in another water molecule, forming a hydrogen bond.   * As a result, water molecules are attracted to one another.

• Because water molecules can form hydrogen bonds, they have qualities that aid in the survival of life on Earth, such as the image attached above.   * %%Water molecules are "sticky," exhibiting cohesive and adhesive properties.%%   * They are attracted to other water molecules as well as other polar compounds.   * This is what gives water its distinct qualities, such as its high surface tension and ability to do so.
• Because of the negative sign in the pH formula, a greater [H+] value results in a lower pH value, and a lower [H+] value results in a higher pH value.   * As a result, a solution with a pH of 3 has a greater [H+] than a solution with a pH of 5.   * @@Furthermore, because the pH scale is logarithmic, a one-unit change in pH translates to a tenfold variation in H+ concentration.@@
• A pH of 3 has ten times the H+ concentration of a pH of 4 and one hundred times the concentration of a pH of 5.   * The pH of a water-based solution is determined by the quantity of dissociated water molecules (split into H+ ions and OH– ions) and the relative quantities of these ions.
• Pure water will dissociate and create equal amounts of H+ and OH– ions, yielding a pH of 7.   * @@Acids raise the relative concentration of H+ ions in a solution, whereas bases raise the concentration of OH– ions in a solution.@@   * Biological systems can be extremely sensitive to pH fluctuations. Buffers are essential for keeping pH levels in live cells generally constant.
• If the pH of a cell falls too low (excess H+), the process will shift to the left, allowing the basic bicarbonate ions to neutralize the excess H+ ions and restore the cell to its original state.   * When the pH of a cell becomes too high (excess OH–), the reaction swings to the right, introducing additional H+ ions into the cell to neutralize the excess OH–, lowering the pH down to normal levels.   * Within a water molecule, oxygen and hydrogen atoms form covalent connections.   * Because oxygen has a higher electronegativity than hydrogen, the electrons in this link are shared unequally, resulting in a polar covalent bond.

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