How can you tell if a molecule is polar or bonded?
Answers
The electronegativity (obtained from periodic table) can be used to determine the polarity.However, the molecular shape is the best, and easiest way to determine whether a molecule is polar or non-polar.
Any molecule that contains a lone pair of electrons on the central atom is polar. For example, H2O is polar because the lone pairs on the oxygen atom create a non-symmetrical shape (bent or v-shaped molecular geometry). Which means no lone pairs is non-polar, right? Wrong. Not all molecules with no lone pairs on the central atom are non-polar. Sure, they might have a linear or tetrahedral shape but it depends on what is bonded to the central atom. For example, CH4 is non-polar whereas a chlorofluorocarbon such as CCl2F2 is polar. Both molecules have the same molecular geometry (tetrahedral) but have different atoms bound to the central atom. CH4 consists of 4 hydrogen atoms bound to the carbon, which has the same difference in electronegativity, and will “cancel out” creating an overall non-polar molecule. CCl2F2 consists of 2 chlorine and 2 fluorine atoms bound to the carbon, the difference in electronegativity is different in the C-F bond and the C-Cl bond, and cannot “cancel out” despite the tetrahedral shape. Therefore, CCl2F2 is polar