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Mastering Lewis Structures: Key Concepts & Examples

Learn how to draw Lewis structures and structural formulas with detailed steps, examples, and practice exercises. Understand expanded valence and drawing structures of ions. Enhance your chemistry skills today!

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Mastering Lewis Structures: Key Concepts & Examples

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  1. Daily Science • Finish the worksheet from last class • If you are finished, help your group

  2. Lewis Structures Pg. 57

  3. Structural Formulas • Used to show relative positions of atoms • Use lines for bonds • Structural formulas are made from Lewis structures

  4. Symbols for Lewis structures • = an electron • = an electron pair • = single bond (σ bond)- 2 electrons • = double bond (σ and π)-4 electrons • = triple bond (σ and 2 π)- 6 electrons

  5. Steps for drawing Lewis Structures • Determine the number of valence electrons for each element • Sum the valence electrons for all the elements • Determine which atom will be the central atom and connect each element with a line. • H and halogens are always terminal • Least electronegative is the central atom • First atom listed is USUALLY the central atom • Each atom (except H and He) must has 8 electrons around it (octet). Complete each octet by adding lone pairs. • Count the number of electrons in your structure • Too many electrons, cross out a lone pair from the central atom and a terminal atom (except H and He) and create a multiple bond • Recount and repeat until the total number of electrons equals the number from number 1

  6. Examples • CCl4 • NF3 • NO2 • CO

  7. Expanded valence • If your total number of electrons in the last step is less than the total in number 1, add a lone pair around the central atom. • This can occur from the 3rd period down • Called an expanded valence • Ex. SeCl4 and PCl5

  8. Lewis structures of ions • Do the same steps and add the extra electrons that are with the ion • If the ion is positive, subtract electrons • If the ion is negative, add ions • Ex. SO42-

  9. PracticePg. 58 • Create a chart like the following taking up the WHOLE page

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