Molecular Interactions Polar and Non Polar Substances

The Polar Nature of Water Polar – bonds with unequal sharing of electrons Polar – bonds with unequal sharing of electrons Electronegativity – the tendency of an atom to attract elections toward itself Electronegativity – the tendency of an atom to attract elections toward itself Non Polar – nearly equal sharing of electrons Non Polar – nearly equal sharing of electrons Dipoles – molecules with positive and negative ends Dipoles – molecules with positive and negative ends

Hydrophilic and Hydrophobic Substances Hydrophillic  Polar covalent compounds (alcohols, ketones)  Sugars  Ionic compounds  Amino acids, phosphate esters Hydrophobic  Non polar covalent compounds (hydrocarbons)  Fatty acids, cholesterol

Hydrogen Bonding Attractions between hydrogen atoms in polar molecules Attractions between hydrogen atoms in polar molecules Low bond energy (the energy needed to break a bond) Low bond energy (the energy needed to break a bond) Relatively weak compared to a covalent bond Relatively weak compared to a covalent bond Can exist within molecules (intramolecular) or between molecules (intermolecular) Can exist within molecules (intramolecular) or between molecules (intermolecular)

The Unique Properties of Water Higher melting and boiling points than other liquids of the same molecular weight Higher melting and boiling points than other liquids of the same molecular weight Maximum density at 4C Maximum density at 4C High specific heat High specific heat High heats of vaporization and fusion High heats of vaporization and fusion Good solvent Good solvent