Polarity

[Cytlalli 1B]

How do you know when a molecule has polarity or is it in every molecule? If so how do you determine which is positive and which is negative?

[Emma Leshan 1B]

You have to look at the electronegativity of each element involved. Technically, every covalent bond has polarity unless it is between 2 of the same elements (O2 for example). However, some bonds are more polar (example: C-H bonds are less polar than O-H bonds) due to the differences in electronegativity between the 2 elements involved.

[Michael Park]

It depends on the electronegativity of each atom in the molecule, so no it cannot be in every molecule. The trend for electronegativity increases up a group and across a period, so elements like fluorine, chlorine, and nitrogen have pretty high electronegativity. This means that they have a greater tendency to attract electrons. Since electrons are negatively charged, these atoms (of fluorine, chlorine, and nitrogen) will be slightly negative.

A good example of this is a water molecule. Oxygen is far more electronegative than hydrogen, so it attracts hydrogen's electrons a little closer to oxygen, which gives it a slightly negative charge.