Writing Lewis Dot Structures Determine the total number of valence electrons in molecule For cations (+) subtract electrons For anions (-) add electrons Write a skeleton structure for molecule Normally the least electronegative element is at the center When possible, use the chemical formula as a hint H’s always, and Halides most often, are terminal (NEVER form multiple bonds) Oxygens do not like to bond together (with a few exceptions) Subtract 2 electrons for each bond in skeleton structure Subtract 2 electrons for each lone pair added to structure Oxygens most often have at least two sets of nonbonding pairs Terminal halides have three sets of lone pairs. Distribute the remaining valence electrons until all atoms have a complete octet May need to introduce multiple bonds (repeat until multiple bonds are not required)

Writing Lewis Dot Structures Example Determine the total number of valence electrons in molecule For cations (+) subtract electrons For anions (-) add electrons Oxygen: 6 x 3 = 18 e - Sulfur: 6 x 1 = 6 e - Total : 24 e - SO 3

Writing Lewis Dot Structures Example Write a skeleton structure for the molecule Normally the least electronegative element is at the center Oxygens do not like to bond together (with a few exceptions) SO 3 O S O O Oxygen: 6 x 3 = 18 e - Sulfur: 6 x 1 = 6 e - Total : 24 e -

Writing Lewis Dot Structures Example From this total, subtract 2 electrons for each bond in skeleton structure O S O O Oxygen: 6 x 3 = 18 e - Sulfur: 6 x 1 = 6 e - Total : 24 e - -Bonds: 2 x 3 = 6 e - Electrons Left: 18 e - SO 3

Writing Lewis Dot Structures Example Oxygens most often have at least two sets of nonbonding pairs Subtract 2 electrons for each lone pair added to structure O S O O Oxygen: 6 x 3 = 18 e - Sulfur: 6 x 1 = 6 e - Total : 24 e - -Bonds: 2 x 3 = 6 e - Electrons Left: 18 e - -LoneP: 2 x 6 = 12e - Electrons Left: 6 e - SO 3

Oxygen: 6 x 3 = 18 e - Sulfur: 6 x 1 = 6 e - Total : 24 e - -Bonds: 2 x 3 = 6 e - Electrons Left: 18 e - -LoneP: 2 x 6 = 12e - Electrons Left: 6 e - Writing Lewis Dot Structures Example O S O O SO 3 wants 2 more electrons There is a “need” of 8 electrons, but there are only 6 left, so 2 must be shared---double bond. Distribute the remaining valence electrons until all atoms have a complete octet May need to introduce multiple bonds (repeat until multiple bonds are not required)

Oxygen: 6 x 3 = 18 e - Sulfur: 6 x 1 = 6 e - Total : 24 e - -Bonds: 2 x 3 = 6 e - Electrons Left: 18 e - -LoneP: 2 x 6 = 12e - Electrons Left: 6 e - -Bond: 2e - Electrons Left: 4e - Writing Lewis Dot Structures Example O S O O SO 3 “happy” wants 2 more electrons “happy” wants 2 more electrons There is a “need” of 4 electrons, but there are 4 left, so just distribute Distribute the remaining valence electrons until all atoms have a complete octet May need to introduce multiple bonds (repeat until multiple bonds are not required)

Oxygen: 6 x 3 = 18 e - Sulfur: 6 x 1 = 6 e - Total : 24 e - -Bonds: 2 x 3 = 6 e - Electrons Left: 18 e - -LoneP: 2 x 6 = 12e - Electrons Left: 6 e - -Bond: 2e - Electrons Left: 4e - -2 Bonds: 4e - 0 Writing Lewis Dot Structures Example O S O O SO 3 “happy” Distribute the remaining valence electrons until all atoms have a complete octet May need to introduce multiple bonds (repeat until multiple bonds are not required)