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How to Figure Out the Polarity

Two atoms form a covalent bond when they equally share a pair of electrons; one electron from each of the two atoms. In contrast, ionic bonds are formed when one of the two atoms has a greater attraction for electrons, measured in a quality called electronegativity. The more electronegative atom takes an electron from its partner and becomes negative, while the other atom becomes positive. The attraction between the two opposite charges then creates a bond. Between these two extremes are bonds which are polarized; the more electronegative atom takes more than its share of electrons and become partially negative. You can calculate the polarity of a bond from the electronegativities of its atoms. (ref 1 and 3)

Things You'll Need

Calculator
Table of elemental electronegativity values

Instructions

- 1
  Find the values of electronegativity for the two elements whose atoms are bonded together. You can find electronegativity tables in standard chemistry textbooks and reference books and they are also often printed on periodic tables. For example, if you were interested in the polarity of the bond between oxygen (O) and hydrogen (H), you would look up the electronegativity values for those two elements. (these sections ref 1)
- 2
  Subtract the lesser of the two electronegativity values from the greater one. In the case of example, the electronegativity of O is 3.5 and H is 2.1, so you would calculate 3.5 minus 2.1 to obtain 1.4.
- 3
  Find the percent ionic character corresponding to the difference in electronegativities that you just determined. You will find a chart of the ionic character of each possible difference in electronegativity values included with electronegativity tables. For the O-H bond, you would look for a difference of 1.4 and find a related percent ionic character of 39%.
- 4
  Compare the percent ionic character you have found for the bond you are investigating to the highest possible value of 95% ionic. The closer your value is to this maximum, the greater the polarity in the bond. The O-H bond has 39% ionic character, which is relatively high and so this bond is partly polar, with a partial negative charge on the oxygen atom.

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