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Clemson BCHM 3050 - The Properties and Importance of Water

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BCHM 3050 Lecture 2 Outline of Last Lecture I. The Phenomenon of IridescenceII. Metric System III. The Importance of WaterIV. BiomoleculesOutline of Current LectureI. Molecular structure of waterII. Bonds III. Non-Polar Covalent bondsIV. Polar Covalent bondsV. Hydrogen BondingVI. Ionic BondsVII. Van der Waals ForcesVIII. Water is an ideal biological solventIX. Hydrophobic EffectX. Solvent Properties of WaterCurrent Lecture I. Molecular structure of Watera. Water constitutes 70-80% of our bodyb. Partial charges on atoms are due to electronegativity & ionic bonds (very electronegative elements are located to the right of the periodic table)c. Charges on H and O as well as sharing of electrons (covalent bond) hold water molecule togetherII. Bondsa. Certain properties of atoms make one more probable to bond with a specific other atomb. Electronegativity – how strongly atoms attract electronsc. Two atoms with similar EN make covalent bondsd. Two atoms with very different EN make ionic bondsIII. Non-Polar Covalent bondsa. - Nonpolar – all atoms have equal rights to electrons; electrons are equidistant from the nucleus of all the atomsThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.IV. Polar Covalent bondsa. Polar covalent – when one atom is more invested than the other in attracting the electrons towards itV. Hydrogen Bondinga. 4 hydrogen bonds formed by 1 water moleculeb. Within one molecule of water, the atoms are polar covalentc. Electrostatic cloud is formed to create hydrogen bondd. Hydrogen bonding is a unique property of watere. Hydrogen bonds are formed BETWEEN (intermolecular) water moleculesf. Polar covalent bonds are formed WITHIN (intramolecular) water moleculesVI. Ionic bondsa. Ionic interactions = electrostatic interactionsb. Ionic bonds = give and take of electronsc. Covalent bonds = sharing of electronsd. Loses electron à gains positive chargee. Na wants to lose electron to have stable conformationf. Na atoms has 11 electrons (2, 8, 1) g. Cl has 17 electrons (2, 8, 7)h. Easiest for Na to donate electron to Cl (Na+Cl-)i. Water can break apart this relationship between Na and Cl due to hydrogen bonding and the partial positive and negative charges of the water moleculesj. Water is a great solvent (especially for ionic compounds)VII. Van der Waals Forcesa. Van der Waals forces are one of the weaker bonds; interaction between dipolesb. They are between different molecules (intermolecular)c. Dipole-induced = CH4 temporarily adopt a dipole due to attraction from other molecules (but wouldn’t normally expect CH4 to have a dipole)VIII. Water is the ideal biological solventa. Partial negative of water attracts other positive ions and partial positive of water attracts other negative ions à Dissociation of solute (ions are surrounded by molecules)b. CH4 is hydrophobic because it doesn’t normally have partial charges on its atoms(but water can still be used to dissolve it)c. Cohesioni. water molecules remain together because of strong hydrogen bondsd. Adhesioni. water interacts with other surfaces (plays role in capillary action of plants)e. Surface Tensioni. allows some organisms to be able to walk on waterii. Based on hydrogen bonding of wateriii. Tension of the surface of the water bodyiv. One molecule of water participates in hydrogen bonding with four other moleculesv. Force exerted by the molecules at the surface is weakervi. The pull downwards is stronger than the pull upwardsf. Ice floats on wateri. Hydrogen bonding creates gaps in the molecules of frozen water which make ice less dense than liquid waterg. Water has a high melting and boiling pointi. Hydrogen bonding makes its resilient and tough to break bonds – much heat and energy needed to break hydrogen bondsIX. Hydrophobic Effecta. Molecule that dissolves in water = hydrophilic; polarb. Molecule that cannot dissolve in water = hydrophobic; nonpolarc. Hydrophobic and hydrophilic molecules together form amphipathic moleculesX. Solvent Properties of Watera. Any solvent tries to form a balance between two sides of the membraneb. Enables movement of a lot of things in our cells across cell membranesc. Osmosis – have diffusion but can be against concentration gradient d. Semi-permeable barrier – lets some things in but not otherse. Amphipathic effect – membrane exerts pressure against molecules being let into the membranef. when cells lose water, they shrinkg. Isotonic solution – ideal solution with same concentrations inside and outside of the cellh. Hypotonic – lesser amount of solute and more of water; water enters the cell, swells, and burstsi. Hypertonic – more solute outside of cell; water leaves


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Clemson BCHM 3050 - The Properties and Importance of Water

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