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CHEM 115
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GUIDELINES for Electron Dot Formulas of Molecules

1. Calculate the total # of valence electrons for all atoms in the compound

  • Number should be even

2. Divide the total number by 2 to get the number of electron pairs

3. Write symbol for central atom (usually underlined or indicated in some way), then put all the other atoms around it.

4. Connect all the atoms together using single bonds.

5. Distribute remaining electrons around outer atoms so they all have an octet (8 e–), except hydrogen (H) only needs 2 electrons.

  • bonding electrons: electron pairs shared between two atoms
  • nonbonding (lone pair) electrons: unshared electron pairs belonging to a single atom

6. If there are not enough electron pairs for all atoms to have an octet, move a nonbonding electron pair from outer atom to a position between the outer atom and the central atom

  • A single pair of e–s between atoms = single bond between the atoms
  • Two pairs of e–s between atoms = double bond between the atoms
  • Three pairs of e–s between atoms = triple bond between the atoms
Last Updated: 06/11/2015
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