Name___________________________________________________Period________
Drawing Lewis Dot Structures Neil 2013:
1) Determine the number of valence electrons for each atom in the molecule/polyatomic
2) Determine the total number of valence electrons for each molecule/ion. In the case of ions, add one electron for
each unit of negative charge or subtract one electron for each unit of positive charge.
3) Draw a “skeleton” structure joining atoms by single bonds. If there is a single atom of one element in a compound,
show it as the central atom with other atoms joined to it. Hydrogen is never a central atom. If there are two single
atoms in a compound, the least electronegative atom should be the central atom
4) From the total number of valence electrons (from step 2) subtract two electrons for each single bond in the skeleton.
The number of electrons remaining tells you how many valence electrons are left to distribute.
5) Use the octet rule to distribute the remaining valence electrons as unshared pairs around the atoms in the molecule
or ion. (Remember: Hydrogen follows the duet rule – it only wants 2 electrons in its outer orbital. Also, because of its
position on the periodic table, Boron only wants 6 electrons.)
6) If you reach the total number of valence electrons (from step 2) and there are too few valence electrons to give each
atom an octet, multiple bonds (double or triple) may be needed. Remember that bonding electrons are “counted
toward both atoms in the bond while unshared electrons are “assigned” to only one atom.
7) Some molecules/ions have multiple arrangements of their bonds and/or unpaired electrons that will satisfy the rules
of Lewis Dot Structures, these are called isomers of each other. (Think of the orange vs. lemon and mint vs. caraway)
8) Complete this chart on the following page:
Name
Molecular Formula
Total Valence Electrons
Lewis Structure
Complete this chart for the following:
Examples: H2O, N2O, NF3 , and NO3-1 – We’ll do these together
You are on your own for these:
8) Acetylene (C2H2)
1) Boron Trichloride (Remember: Boron doesn’t follow
the octet rule – see step 5)
9) Phosphorus Trichloride
2) Methane (CH4)f
3) Ethylene (C2H4)
10) Carbon Tetrachloride
11) Carbonate Ion (this has 3 isomers draw them all)
4) Ammonia
12) Thiocyanate Ion (SCN-1) (this has 2 isomers, draw
both)
5) Ammonium
13) Carbon Disulfide
6) Hydrogen Sulfide or Hydrosulfuric Acid
14) Formaldehyde (H2CO)
7) Sulfur Trioxide (this has 3 isomers draw them all)
Name
1.
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Molecular
Formula
Total Valence
Electrons
Lewis Dot Structure