Lecture 2 Notes (1/23/15)Office hours—Bryan Phillips—W&Th 9:00-10:30Learning ObjectivesReactivity of atoms and molecule formationTypes of chemical bonds and molecular interactions in living organismsProperties of water and the significance of those properties for life-Atoms in the same column have the same number of electrons in the valence shellThese two bonds give stability to atoms by giving full outer electron shells:Covalent bond: Sharing of electron pairs (Strong)Ionic bond: Involves the transfer of an electron from one interacting atom to the other atom and the subsequent electrical attraction between ions of opposite charge-Sharing of electrons in a covalent bond is not always equalSome atoms have greater electronegativityElectronegativity is the attractive force that an atomic nucleus exerts on shared electronsIt depends on the number of protons and the distance between the nucleus and electrons-When sharing is UNEQUAL, a Polar Covalent Bond is formedEX: H2O, which can interact with both positively and negatively charged molecules-When one atom is much more electronegative than the other, a complete transfer (donation) of electrons may occur-This results in two oppositely charged ions with full outer electron shellsCations = Positive (+)Anions = Negative (-)-Ionic bonds are formed by the electrical attraction of cations and anions (ionic compound)This bond can form between or within molecules:Hydrogen bond: Electrical attraction between a positively charged hydrogen atom and a negative atom (N or O)-Polar molecules are attracted to water-Non polar molecules are more attracted to one another than to waterWater: The liquid of life-It’s structure gives it unique and versatile propertiesPolar moleculesBonds with other water molecules-The polar covalent bonds of water make it the best solvent aroundPolar and ionic compounds dissolve easilyMost of the chemical reactions of living organisms occur in the water-filled cells-Water ionizes in cells pH: Negative log of molar concentration of H+ ions-Pure water has a pH of 7 (neutral)Acids and Bases Acid: When dissolved, releases hydrogen ions-H+ ions can attach to other molecules and change their propertiesStrong acid=dissociates completely in waterWeak acid=incomplete dissociation Base: Accept hydrogen ions –––––––––––Strong base=dissociates completely Weak base=dissociates incompletely-Life can only exist in a small pH rangeBuffer: Help maintain constant pH by absorbing or releasing H+ ions-Is a weak acid and its corresponding baseClicker Questions-Most common molecule found in living organisms=water-If a molecule is hydrophilic it is both polar and has a partially positive and partially negative