The difference in the electronegativity between two atoms is an indicator of the polarity of the bond between the elements. The difference ranges from 0 to about 3, and the bond ranges from nonpolar to polar to ionic.
The position of an element on the periodic table indicates the number of valence electrons on an atom. The key to a Lewis dot diagram is the sum of the valence electrons of all atoms in a species plus electrons indicated by the charge on an anion (negative ion) or minus electrons indicated by the charge on a cation (positive ion). A correct diagram must indicate all of these electrons. The bonds and lone pairs around an atom in a Lewis dot diagram indicate the shape and polarity of the species.
The Problems You’ll Work On
In this chapter, you work with molecular geometry in the following ways:
Counting electrons in Lewis dot diagrams
Predicting bond types based on electronegativity values
Recognizing molecular shapes
Identifying polarity in bonds and molecules
Note: For access to the periodic table, see the Appendix.
What to Watch Out For ...