1. Drawing Lewis Structures A Tutorial on Writing Lewis Dot Structure

2. Drawing Lewis Dot Structures
Know how to determine the valence electrons for all elements.
Connectivity: From the chemical formula, determine the atom connectivity for the structure.
i. Given a chemical formula, ABn, A is the central atom and B flanks the A atom. i.e., NH3, NCl3, NO2. In these examples, N is central in the structure.
ii. H and F are never central atoms. Usually, the atom that needs the most electrons is in the center of the molecule/ion.
Draw individual Lewis Dot structures for all atoms. Start connecting each atom to the central atom using a single bond. Count the number of electrons on each atom. If an atom has an octet, there’s a good chance it is complete. If it does not, continue to connect bonds to the central atom.
3. For atoms that do not have octets after all possibilities are exhausted, Use the remaining unbonded valence electrons (normally on the central atom) to satisfy the octet. If drawing the Lewis Dot Structure of an ion, remember to use the extra electrons! Assign formal charges to each atom where electrons have moved to and from.

3. Valence electrons for Elements
Recall that the valence electrons for the elements can be determined based on the elements position on the periodic table.
Lewis Dot Symbol

4. Valence electrons and number of bonds
Number of bonds elements prefers depending on the number of valence electrons. In general -  F a m i l y # C o v a l e n t B o n d s* H a l o g e n s F , B r C I  X
1 bond often  C a l c o g e n s O , S
2 bond often O 
3 bond often N i t r o g e n , P N 
4 bond always C a r b o n , S i C
The above chart is a guide on the number of bonds formed by these atoms.

5. Atomic Connectivity
The atomic arrangement for a molecule is usually given.
CH2ClF HNO3 CH3COOH H2Se H2SO4 O3 H C F Cl H N O
H C C
O H H O
H O S
O H O H Se O
In general when there is a single central atom in the molecule, CH2ClF, SeCl2, O3 (CO2, NH3, PO43-), the central atom is the first atom in the chemical formula.
Except when the first atom in the chemical formula is Hydrogen (H) or fluorine (F). In which case the central atom is the second atom in the chemical formula.
Find the central atom for the following:
1) H2O a) H b) O 2) PCl3 a) P b) Cl
3) SO3 a) S b) O 4) CO32- a) C b) O
5) BeH2 a) Be b) H 6) IO3- a) I b) O

6. Lewis Dot Structure of HNO3
A) Determine the central atom:
E) Assign formal charges:
B) Draw skeleton, place valence electrons:
F) Don’t forget about overall charges!:
C) Connect electrons to central atom:
Writing Lewis Structure:
D) Count up electrons, move electrons if necessary:

7. Lewis Dot Structure of ClO4-
A) Determine the central atom:
E) Assign formal charges:
B) Draw skeleton, place valence electrons:
F) Don’t forget about overall charges!:
C) Connect electrons to central atom:
Writing Lewis Structure:
D) Count up electrons, move electrons if necessary:

8. Lewis Dot Structure of CO3 2-
A) Determine the central atom:
E) Assign formal charges:
B) Draw skeleton, place valence electrons:
F) Don’t forget about overall charges!:
C) Connect electrons to central atom:
Writing Lewis Structure:
D) Count up electrons, move electrons if necessary:

9. Lewis Dot Structures:
Example
a) CH2ClF b) SO2
c) SO42- d) H3PO4