BIO 202 Lecture 1

• The electronegativity difference between two atoms determines the polarity of a bond.
• Polar bonds is the unequal sharing of electrons. Electrons are shifted toward the nucleus of the more electronegative atom.
• Non-polar bonds are the equal sharing of electrons. Electrons are at equal distances from the nucleus of the atoms.
• Two types of weak bonds are van der Waals and hydrogen bonds.
• Oxygen is the most electronegative element, so all electrons shift towards it.
• Ionic bonds happen when electrons are stripped from the less electronegative atom.
• Ionic bonds are also known as salts.
• Ionic compounds can be a combination of cations and anions.
• Dry ionic bonds are strong. They form salt crystals.
• Wet ionic bonds are weak. Salt crystals dissolve in water.
• Weak bonds are needed for: temporary association between molecules and for signaling molecules.
• Hydrogen bonds happen when hydrogen is bonded to one electronegative atom, which that hydrogen is also attracted to another electronegative atom of a different molecule.
• The electronegative atom is usually nitrogen or oxygen.
• Van der Waals bond is when non polar molecules have hot spots and temporary charges made from electron movement. These charges let molecules temporarily interact.
• The properties of water are: cohesive behavior, ability to stabilize temperature, expansion upon freezing, and solvent versatility.
• Hydrogen bonds give water adhesive and cohesive properties.
• Water can go up through capillary tubes of plant vascular systems or for insects to walk on water.
• Water has high specific heat meaning it requires more energy to heat it up because it has a lot of hydrogen bonds.
• Water moderates the climate on Earth by absorbing and storing sun energy.
• Formation of ice changes the temperature of fall to winter because the forming of hydrogen bonds release heat and ice has way more hydrogen bonds than water.
• Cells are adaptable to temperature changes because they are made of mostly water.
• The density of water is greater than the density of ice.
• The hydrogen bonds in ice keep the molecules further apart so the ice becomes less dense.
• Large bodies of water does not freeze all the way to the bottom, preserving life because the ice floats on top.
• Polar bonds in water make it an active solvent, able to dissolve many substances.
• Non ionic molecules like sugars can dissolve in water.
• Water is a good solvent in biological solutions like plant sap and blood serum
• Substances that dissolve in water are hydropillic and have ionic or polar bonds.
• Substances that do not dissolve in water are hydrophobic and have non polar bonds
• Water can dissociate meaning an electron get attracted to oxygen and leaves hydrogen altogether. It becomes (H+) + (OH-).
• To change concentration of H+ or OH-, you can dissolve in water a substance that adds H+ or OH-.
• Increase H+ are called acids.
• Increase OH- are bases.
• Pure water has equal concentration of H+ and OH- of 10^-7 each.
• Water is neutral
• PH= -log [H+]
• Acidic is when the pH is less than 7
• Basic is when the pH is more than 7.
• Neutral is at 7
• PH changes are harmful because they can inactivate and destroy biological molecules like proteins and nucleic acids.