Molecular Geometry Lewis Structures VSEPR Theory

Lewis Structures Count up the total number of valence electrons Draw single bonds between central atom and surrounding atoms Place remaining electrons, in pairs around appropriate atoms Start with outer atoms Make sure all atoms that need octets have octets Make double bonds if necessary Draw resonance structures (if applicable)

Lewis Structures Examples

Lewis Structures Ex: H2O 1. # valence electrons 2. Draw single bond between atoms. 3. Place remaining electrons around appropriate atoms.

Lewis Structures Ex: PF3 1. # valence electrons 2. Draw single bond between atoms. 3. Place remaining electrons around appropriate atoms, starting with outer atoms.

Lewis Structures Ex: NH41+ 1. # valence electrons 2. Draw single bond between atoms. 3. Place remaining electrons around appropriate atoms, starting with outer atoms.

Lewis Structures Ex: NO21- 1. # valence electrons 2. Draw single bond between atoms. 3. Place remaining electrons around appropriate atoms, starting with outer atoms.

Lewis Structures Check octets of each atom.

Lewis Structures Nitrate can have two resonance structures because the valence electrons are free to move over the entire structure of the polyatomic.

Lewis Structures  Formal Charge When lewis structures have resonance structures, then the most preferred resonance structure is the one with the lowest formal charge. Take last example:

Lewis Structures  Formal Charge Formal Charge = V – N – ½(B) (valence electrons) – (nonbonding electrons) – ½ (bonding electrons)

Formal Charge Formal charges should be as low as possible. Formal charges of every element that makes up the molecule should equal the overall charge of the molecule.

Formal Charge Negative formal charges should be on the more electronegative atom (elements closest to fluorine). Positive formal charges should be on the less electronegative atoms.

Valence Shell Electron Repulsion Theory (VSEPR) Electron Groups Bonding Groups Lone Pairs Electron Geometry Molecular Geometry Approximate Bond Angles 2 Linear 180° 3 Trigonal Planar 120° 1 Bent <120° 4 Tetrahedral 109.5° Trigonal Pyramidal <109.5°

VSEPR Determine the lewis structure and molecular shape of: CO2 # Valence electrons: Lewis Structure: Electron Geometry: Molecular Geometry:

VSEPR Determine the lewis structure and molecular shape of: BF3 # Valence electrons: Lewis Structure: Electron Geometry: Molecular Geometry:

VSEPR Determine the lewis structure and molecular shape of: SO2 # Valence electrons: Lewis Structure: Electron Geometry: Molecular Geometry:

VSEPR Determine the lewis structure and molecular shape of: CH4 # Valence electrons: Lewis Structure: Electron Geometry: Molecular Geometry:

VSEPR Determine the lewis structure and molecular shape of: NH3 # Valence electrons: Lewis Structure: Electron Geometry: Molecular Geometry:

VSEPR Determine the lewis structure and molecular shape of: H2O # Valence electrons: Lewis Structure: Electron Geometry: Molecular Geometry:

Valence Shell Electron Repulsion Theory (VSEPR)

Polar Bonds Created when electrons are drawn more closely to one of the atoms in the bond The bond is polarized Electrons are pulled toward more electronegative atoms Electronegative atoms: atoms that strongly attract bonding electrons Most electronegative element: Fluorine

Polar Bonds Symbolize polar bonds with δ Can also symbolize by

Polar Bonds Examples:

Polar Bonds Examples:

Polar Bonds Examples:

Hybridization Hydridization occurs to allow the atoms of the molecule to spread further away from each other S orbitals and P orbitals hybridize into sp, sp2, and sp3 orbitals Anything above sp3 does not occur because there are only 3 p orbitals Therefore, DO NOT write sp4 , ect. Also, there is only one s orbital, therefore, DO NOT write s2p3, ect

Hybridization Note: We only look at hybridization in terms of the central atom.

Hybridization – The Short Cut

sp3 Hybridization

sp2 Hybridization

sp Hybridization

Determine the Hybridization of each of the following

Electron Geometry Molecular Geometry (Shape) Hybridization Lewis structure (shown) Electron geometry (central atoms) Molecular geom. (central atoms) Hybridization of central atoms Bond angles

Electron Geometry Molecular Geometry (Shape) Hybridization Lewis structure (shown) Electron geometry (central atoms) Tetrahedral Trigonal planar Molecular geom. (central atoms) Hybridization of central atoms Bond angles 1 2 3 4

Electron Geometry Molecular Geometry (Shape) Hybridization Lewis structure (shown) Electron geometry (central atoms) Molecular geom. (central atoms) Trigonal pyramidal Tetrahedral Trigonal planar Bent Hybridization of central atoms Bond angles 1 2 3 4

Electron Geometry Molecular Geometry (Shape) Hybridization Lewis structure (shown) Electron geometry (central atoms) Molecular geom. (central atoms) Hybridization of central atoms sp3 sp2 Bond angles 1 2 3 4

Electron Geometry Molecular Geometry (Shape) Hybridization Lewis structure (shown) Electron geometry (central atoms) Molecular geom. (central atoms) Hybridization of central atoms Bond angles <109.5 109.5 ~120 1 2 3 4