EXAMINING POLARITY MICRO-TO-MACRO We have studied the shapes and structures of molecules The shape of a molecule affects how that molecule behaves The behavior of each molecule affects what a material is like Example Waters bent structure makes it polar (partially positive and negative on different sides). This makes it dissolve things easily, reactive, amphoteric, lower density when a solid, etc. POLARITY One of the major predictors of how a molecule will behave is polarity Polarity is when a molecule has partial positive and negative charges Polarity is caused by a combination of asymmetry and polar bonds POLAR BONDS If a molecule with high electronegativity is covalently bonded to a molecule with low electronegativity this creates a polar covalent bond Every element has a value for electronegativity If the difference between the atoms electronegativies are: Less than 0.4 = Nonpolar Covalent totally equal sharing of electrons Between 0.4 & 1.6 = Polar Covalent Non-equal sharing of electrons Greater than 1.6 = Ionic Transfer of electrons ** IONIC COMPOUNDS ARE NOT POLAR. They have actually exchanged electrons and have real CHARGES ** POLAR BONDS This unequal sharing of electrons results in a concentration of electrons on one side and a lack of electrons on the other This creates a partial charge Partial charges are areas where the compound is slightly negative or positive The element with the higher electronegativity will have more electrons around it and will be slightly negative EXAMPLES Are the following bonds ionic, covalent, or polar covalent? If the bond is polar covalent, which element would have a partial negative and a partial positive charge? Cl-Cl B-H Na-Cl C-Cl SHAPE Polar covalent bonds arent enough to make a polar compound Polar compounds must have asymmetry If there is an equal pulling of electrons in every direction, the result is a non-polar molecule **Keep in mind that electrons have a negative charge. If there are lone pairs of electrons on one side (and it is asymmetrical) these may contribute to polarity** IN DEPTH EXAMPLE Water H 2 O EXAMPLES Are the following compounds polar or non-polar? CO 2 CH 2 Cl 2 HCN BCl 3