BCHM 3050 Lecture 2 Water I II III IV V VI Molecular structure of Water a Water constitutes 70 80 of our body b 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 together Bonds a Certain properties of atoms make one more probable to bond with a specific other atom b Electronegativity how strongly atoms attract electrons c Two atoms with similar EN make covalent bonds d Two atoms with very different EN make ionic bonds Non Polar Covalent bonds a Nonpolar all atoms have equal rights to electrons electrons are equidistant from the nucleus of all the atoms Polar Covalent bonds a Polar covalent when one atom is more invested than the other in attracting the electrons towards it Hydrogen Bonding a 4 hydrogen bonds formed by 1 water molecule b Within one molecule of water the atoms are polar covalent c Electrostatic cloud is formed to create hydrogen bond d Hydrogen bonding is a unique property of water e Hydrogen bonds are formed BETWEEN intermolecular water molecules f Polar covalent bonds are formed WITHIN intramolecular water molecules Ionic bonds a Ionic interactions electrostatic interactions b Ionic bonds give and take of electrons c Covalent bonds sharing of electrons d Loses electron gains positive charge e Na wants to lose electron to have stable conformation f 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 These 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 i VII VIII IX X Water can break apart this relationship between Na and Cl due to hydrogen bonding and the partial positive and negative charges of the water molecules j Water is a great solvent especially for ionic compounds Van der Waals Forces a Van der Waals forces are one of the weaker bonds interaction between dipoles b 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 Water is the ideal biological solvent a Partial negative of water attracts other positive ions and partial positive of water attracts other negative ions 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 Cohesion i water molecules remain together because of strong hydrogen bonds d Adhesion i water interacts with other surfaces plays role in capillary action of plants e Surface Tension i allows some organisms to be able to walk on water ii Based on hydrogen bonding of water iii Tension of the surface of the water body iv One molecule of water participates in hydrogen bonding with four other molecules v Force exerted by the molecules at the surface is weaker vi The pull downwards is stronger than the pull upwards f Ice floats on water i Hydrogen bonding creates gaps in the molecules of frozen water which make ice less dense than liquid water g Water has a high melting and boiling point i Hydrogen bonding makes its resilient and tough to break bonds much heat and energy needed to break hydrogen bonds Hydrophobic Effect a Molecule that dissolves in water hydrophilic polar b Molecule that cannot dissolve in water hydrophobic nonpolar c Hydrophobic and hydrophilic molecules together form amphipathic molecules Solvent Properties of Water a Any solvent tries to form a balance between two sides of the membrane b Enables movement of a lot of things in our cells across cell membranes c Osmosis have diffusion but can be against concentration gradient d Semi permeable barrier lets some things in but not others e Amphipathic effect membrane exerts pressure against molecules being let into the membrane f when cells lose water they shrink g Isotonic solution ideal solution with same concentrations inside and outside of the cell h Hypotonic lesser amount of solute and more of water water enters the cell swells and bursts i Hypertonic more solute outside of cell water leaves cell