Lewis Diagrams

Lewis Structures Find your element on the periodic table. Determine the number of valence electrons. This is how many electrons you will draw.

Lewis Structures Find out which group (column) your element is in. This will tell you the number of valence electrons your element has. You will only draw the valence electrons.

Except for He, it has 2 electrons Group 2 = 2 electrons 3, 4, 5, 6, 7 Each column is called a “group” Each element in a group has the same number of electrons in their outer orbital, also known as “shells”. The electrons in the outer shell are called “valence electrons”

C Lewis Structures Write the element symbol. Carbon is in the 4th group, so it has 4 valence electrons. Starting at the right, draw 4 electrons, or dots, counter-clockwise around the element symbol. C

C Lewis Structures Check your work. Using your periodic table, check that Carbon is in the 4th group. You should have 4 total electrons, or dots, drawn in for Carbon. C

C Lewis Structures On your worksheet, try these elements on your own: P Ca Ar Cl Al C

H Lewis Structures On your worksheet, try these elements on your own: P Ca Ar Cl Al H

P Lewis Structures On your worksheet, try these elements on your own: Ca Ar Cl Al P

Ca Lewis Structures On your worksheet, try these elements on your own: P Ca Ar Cl Al Ca

Ar Lewis Structures On your worksheet, try these elements on your own: P Ca Ar Cl Al Ar

Cl Lewis Structures On your worksheet, try these elements on your own: P Ca Ar Cl Al Cl

Al Lewis Structures On your worksheet, try these elements on your own: P Ca Ar Cl Al Al

Octet Rule Remember… Most atoms form bonds in order to have 8 valence electrons.

F B F F H O H N O F F F S F Very unstable!! A. Octet Rule Exceptions: Hydrogen  2 valence e- Groups 1,2,3 get 2,4,6 valence e- Expanded octet  more than 8 valence e- (e.g. S, P, Xe) Radicals  odd # of valence e- C. Johannesson

Drawing Lewis Diagrams Find total # of valence e-. Arrange atoms - singular atom is usually in the middle. Form bonds between atoms (2 e-). Distribute remaining e- to give each atom an octet (recall exceptions). If there aren’t enough e- to go around, form double or triple bonds.

Drawing Lewis Diagrams CF4 1 C × 4e- = 4e- 4 F × 7e- = 28e- 32e- F F C F - 8e- 24e-

B. Drawing Lewis Diagrams BeCl2 1 Be × 2e- = 2e- 2 Cl × 7e- = 14e- 16e- Cl Be Cl - 4e- 12e-

B. Drawing Lewis Diagrams CO2 1 C × 4e- = 4e- 2 O × 6e- = 12e- 16e- O C O - 4e- 12e-

Polyatomic Ions To find total # of valence e-: Add 1e- for each negative charge. Subtract 1e- for each positive charge. Place brackets around the ion and label the charge.

O O Cl O Polyatomic Ions ClO4- 1 Cl × 7e- = 7e- 4 O × 6e- = 24e- 31e-

H H N H Polyatomic Ions NH4+ 1 N × 5e- = 5e- 4 H × 1e- = 4e- 9e- - 1e-

Resonance Structures Molecules that can’t be correctly represented by a single Lewis diagram. Actual structure is an average of all the possibilities. Show possible structures separated by a double-headed arrow. C. Johannesson

Resonance Structures SO3 O O S O O O S O O O S O C. Johannesson