posted by Megan .
How do I decide whether something is polar or not?
Polar occurs whenever we have opposit charged ions. such HF, H being positively charged ion and F being negatively charged ion.
Non Polar occurs whenever the two ions are identical. such as Hydrogen ion mixing with another Hydrogen ion to form hydrogen molecules because the ywo hydrogen are positively charged ions.
For binary compounds, a difference in electronegativity leads to a polar compound. For example, CsF. Cs as EN of about 0.8 or so and F has EN of about 4.0. The difference is >3.0 and this is an ionic (polar) compound.
For molecules, two criteria must be satisfied.
a. There must be an EN difference between the central atom and at least one of the other atoms AND (not or)
b. The compound must NOT be symmetrical in three dimensions. An example is CH4 (EN difference between C and H) BUT the molecule is symmetrical. NH3, EN difference AND it is not symmetrical (NH4^+ is symmetrical but not NH3).