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Lewis Dot StructureHow to create a…
#1 Count the total number of valence electrons in the molecule
C: 4 electrons x 1 atom = 4 valence electronsH: 1 electron x 4 atoms = 4 valence electrons
Total = 8 valence electrons
…for CH4
Lewis Dot StructureHow to create a…
#2 Find the number of “octet” electrons for the molecule.
C: 8 octet electrons x 1 atom = 8 octet electronsH: 2 octet electrons x 4 atoms = 8 octet electrons
Total = 16 octet electrons
Rules: Hydrogen always has 2 octet electronsBeryllium always has 4 octet electronsBoron wants 6 for neutral molecules (8 if it’s an anion)
…for CH4
Lewis Dot StructureHow to create a…
#3 Subtract the number of valence electrons from the
number of octet electrons to find the number of bonding
electrons.
16 – 8 = 8 bonding electrons
…for CH4
Lewis Dot StructureHow to create a…
#4 Divide the number of bonding electrons by 2 to find the number of bonds in the
molecule.
8 / 2 = 4 bonds in CH4
Why 2? Because there are two electrons in every covalent bond!
…for CH4
Lewis Dot StructureHow to create a…
#5 Draw an arrangement of atoms that has the number of bonds you found in step 4. Of course, there are more rules…
Hydrogen and Halogens = bond once!Oxygen’s family and Beryllium bond twice in neutral
moleculesNitrogen’s family and Boron bond 3 times in neutral
moleculesCarbon’s family = bonds 4 times!
…for CH4
Lewis Dot StructureHow to create a…
More hints…
If you bond everything together and you have bonds left over, look for
double/triple bonds.
The atom nearest to the left side of the periodic table is probably in the
middle of the molecule.
…for CH4
Draw the Lewis structures for the following compounds:
H2O
CCl4
NH3
CO2
PCL3
Draw the Lewis structures for the following compounds:
N2
CH4
C2H6
CH3OH
BH3
Draw the Lewis structures for the following compounds:
PBr3
N2H2
C2H2
SiH4
C2H4
Draw the Lewis structures for the following compounds:
HF
HCl
CCl2F2
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