Lewis Dot Accounting Ledger Method. Writing Lewis Dot Structures Determine total number of valence electrons in molecule. For cations (+) subtract electrons.

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Lewis Dot Accounting Ledger Method

Writing Lewis Dot Structures Determine total number of valence electrons in molecule. For cations (+) subtract electrons. For anions (-) add electrons. Write skeleton structure for molecule. Normally the least electronegative element at the center. When possible, use the chemical formula a hint. H’s always, and Halides most often, 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 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 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

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

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 - Writing Lewis Dot Structures Example SO 3

Subtract 2 electrons for each lone pair added to structure. Oxygens most often have at least two sets of nonbonding pairs. 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 - Writing Lewis Dot Structures Example 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 = 12 e - Electrons Left: 6 e - O S O O 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 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 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 = 12 e - Electrons Left: 6 e - -Bond: 2 e - Electrons Left: 4 e - O S O O “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 Writing Lewis Dot Structures Example SO 3 Distribute 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 = 12 e - Electrons Left: 6 e - -Bond: 2 e - Electrons Left: 4 e - -2 LoneP: 4 e - Electrons Left: 0 O S O O “happy” Writing Lewis Dot Structures Example SO 3 Distribute remaining valence electrons until all atoms have a complete octet. May need to introduce multiple bonds (repeat until multiple bonds are not required).

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