1. Lewis Dot Structures
Mr. Garcia

2. Valence electrons – electrons in an atom’s highest energy level
Outermost electrons of the electron cloud
Gives elements chemical characteristics
Only electrons shown in Lewis electron dot structures
Symbolized as dots

3. Valence Electrons
Number of valence electrons is the same as the group number for representative elements
Explains why elements of same families have similar characteristics

4. Valence Electrons
Most elements gain or lose valence electrons to have noble gas stability
Noble gas stability- Having full outer shell of electrons
Example: Sodium react violently with chlorine to make NaCl (table salt).

5. Drawing Lewis Dot Structures
Step 1: Identify the symbol for the element and its number of valence electrons using the periodic table.
Step 2: Put the number of electron dots around the symbol. Begin by assigning one dot per side, moving clockwise around the symbol. Start adding a second dot to each side until all of the valence electrons have been placed
The four sides represent the four orbitals in the outermost energy level of an atom of a representative element. These electrons are all negatively charged, so they repel each other and will not pair up until there is one electron in each orbital. Dot structures should never have more than two dots on any side.

6. Lewis Dot Structure - Sulfur
Step 1: Find the element and number of electrons
Answer: Column number 6 (6 valence electrons)
Step 2: Put the number of electron dots around the symbol. Begin by assigning one dot per side, moving clockwise around the symbol. Start adding a second dot to each side until all of the valence electrons have been placed
Answer:

7. Compounds
Line up single dots to form compounds and to make either 2 or 8 electrons around each element. The elements share their single unpaired electrons.

8. 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.

9. Types of Bonds
Chemical Bond- mutual electrical attraction between the nuclei and the valence electrons of different atoms
Ionic Bonds- electrical attraction between cations(-) and anions(+)
Covalent Bonds- the sharing of electron pairs between two atoms

10. Draw the Lewis Dot Structure for CH3I
Step 1: Determine the atoms and the number of each element
Answer: One Carbon, Three Hydrogen, and one Iodine
Step 2: Write the dot structures for each
Answer: Carbon (4 valence e-), Hydrogen (1 valence e-), and Iodine (7 valence e-)

11. Draw the Lewis Dot Structure for CH3I
Step 3: Determine the Total Number of valence electrons to be combined
Answer:
Carbon 1x4e- =4 electrons
Iodine 1x7e- =7 electrons
Hydrogen 3x1e- =3 electrons Total: 14 valence electrons
Step 4: Form a skeletal structure; if carbon is present put it in the middle. If not, the most electronegative is in the middle. Connect with electron pairs.

12. Draw the Lewis Dot Structure for CH3I
Add unshared electrons to non-metals so they have 8 electrons (except hydrogen). Follows the octet rule.
Count the electrons to make sure we used the correct amount and each element follows the octet rule (except Hydrogen)

13. More on Lewis Structures
Electron pairs can also be shown as lines
Some chemical compounds have multiple bonds

14. Draw the Lewis Dot Structure for CH2O
Step 1: Determine the atoms and the number of each element
Answer: One Carbon, Two Hydrogen, and One Oxygen
Step 2: Write the dot structures for each
Answer: Carbon (4 valence e-), Hydrogen (1 valence e-), and Oxygen (6 valence e-)

15. Draw the Lewis Dot Structure for CH2O
Step 3: Determine the Total Number of valence electrons to be combined
Answer:
Carbon 1x4e- =4 electrons
Oxygen 1x6e- =6 electrons
Hydrogen 2x1e- =2 electrons Total: 12 valence electrons
Step 4: Form a skeletal structure; if carbon is present put it in the middle. If not, the most electronegative is in the middle. Connect with electron pairs.

16. Draw the Lewis Dot Structure for CH2O
Step 5: Add unshared electrons to non-metals so they have 8 electrons (except hydrogen). Follows the octet rule.
Step 6: Count the electrons to make sure we used the correct amount and each element follows the octet rule (except Hydrogen)
16 Valence electrons WRONG!

17. Draw the Lewis Dot Structure for CH2O
Step 6 (b): If too many electrons are present, add some lone pairs to bond (multiple bonds). When you add an extra bond, remove another lone pair from carbon.

18. Resonance Structures
Compounds that are represented by a variety of ways, multiple Lewis Dot Structures possible.
Example Ozone (O3)
More Examples: