Electron Dot & Lewis Dot Structures

• Picture representation of the valence electron configuration around an atom.
• Valence electrons represented by dots.
• Nucleus represented by atomic symbol.
• Electrons are placed up to two on each side of the symbol for a maximum of eight, which is a full shell.
• A single electron is placed on each side before pairing them.
• Hydrogen and Helium, only a maximum of 2 electrons (exception).
• Lines between atoms indicate chemical bonds.
• Single lines --> single bonds
• Double lines --> double bonds
• Triple lines --> triple bonds
• Hydrogen and Fluorine never go in center "nucleus"
• Metals are in center
• When one element is singled out, it goes in the center.

Octet Rule

Atoms that combine and form bonds either by transferring electrons to form ions or by sharing electrons in covalent bonds until valence shells are full.

• CNOF (Carbon, Nitrogen, Oxygen and Fluorine) always follow octet rule.

Steps to Drawing a Lewis Structure

1)  Pick a Central Atom

• Pick atom with lowest electronegativity
• Central atom: one furthest from obtaining a full shell.
• Connect other atoms with a single bond.
• They might change to double or triple bonds.

2)  Count Electrons

• Only worry about the shells in the outer shells.
• Apply Octet Rule: valence shell must contain 8 electrons to be stable.

3)  Place Electrons around Atoms

• Once you know how many electrons to draw around each atom, place them on structure.
• When lone pairs are placed, find atoms that do not fulfill octet rule.
• There may be double or triple bonds formed 
• **A pair of electrons form a bond.
• Once electrons are placed, put brackets around the entire structure, if there is a charge on the molecule, write it as a subscript on the upper right, outside the brackets.

Examples:

H₂ 

  


_Cl2    
         

H₂O  

        

NH₃
      

CH₄     

      

O2
   
   

N₂    

                          

 NH₄⁺

 

CO₃^2-

 
^{Open circles represent 2 extra electrons from 2- charge.}