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