Polar Covalent Bonds 10 3 13 Always one bond to hydrogen Polar Covalent Bonds HCl When atoms are not identicle More negative charge around Cl than hydrogen Lowercase delta o Positive partial positive Less likely to find electrons on that side of the molecule o Negative partial negative More electronegative atom Electronegativity Classify atoms with numbers of such Fl has a value of 4 o Most electronegative Metallic elements have low electronegativities Halogens and reactive non metals have high electronegativities Using electronegativity differences to determine if a bond is polar 4 or below non polar covalent bond 5 1 9 indicate increasingly polar bonds 2 or more indicate substancially ionic bonds Calculate for each individual BOND not entire molecules Polar Molecules Due to individual bond polarities and lone pair contributers Electrons displaced toward more negative atom No charge on central molecule Non polar molecules Carbon dioxide o Polar covalent within zero net polarity Attraction Between Molecular Compounds Ionic compounds have a high melting and boiling point Attractive forces between oppositely charged ions are strong Molecules are neutral o No strong attraction to hold them together o Held by weaker forces called intermolecular forces Attraction forces determine the phase of the substance Very weak intermolecular forces gas Somewhat stronger intermolecular force liquid Strongest intermolecular forces molecular solid o Reflected in boiling point and melting point of molecule Intermolecular forces A force that acts between molecules and holds molecules close to one another Three major types o Dipole dipole o Hydrogen bonds o London dispersion forces Between distinct molecules Dipole dipole forces Partial positive on one molecule interacts with a patial negative o Ends of polar molecules are attracted to one another o Since its not full it is looser Hydrogen Bond Lone pair of electrons o O N F atoms and a partial positive charge hydrogen bond o Hydrogen bond is NOT a covalent bond o Intermolecular FORCES Dotted lines Liquid water o Distinct water molecules o Intermolecular forces such as hydrogen bonds occur between distinct water molecules London Dispersion forces Major attractive force between non polar molecules Temporary dipoles Shifts in electrons between two molecules Even distribution Relative strengths Less energy to disrupt less strong forces Same size molecule weakest Strongest when mixed