# Molecular Geometry VSEPR Theory.

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Molecular Geometry VSEPR Theory

Objective to predict the molecular shape for molecules using Valence Shell Electron Pair Repulsion (VSEPR) theory. shapes to know: linear bent trigonal planar tetrahedral

Review / Warmup Draw the lewis dot structure for:
1) CO2 - Carbon Dioxide 2) H2O - Water 3) BF3 - Boron Triflouride 4) CH4 - methane

VSEPR Theory Lewis dot structures are good representations of how molecules are put together, but they fail to show the correct three-dimensional shape of molecules. The VSEPR theory states that electron pairs repel each other, so molecules acquire shapes that make sure these pairs are as far apart as possible.

VSEPR Theory What does VSEPR stand for?
VSEPR = Valence Shell Electron Pair Repulsion

Molecular Geometry Three step process for determining the shape of a molecule First draw the Lewis dot structure Count the number bonded atoms and lone pairs on the central atom. Select the shape that matches the count for bonded atoms and lone pairs on the central atom.

VSEPR Theory CO2 has two bonded oxygens to the central atom.
carbon dioxide Lewis Dot Structure 180o CO2 has two bonded oxygens to the central atom. Each oxygen bonded to the central carbon is positioned as far apart from each other as possible, giving the carbon dioxide molecule a linear shape. The bond angle between each oxygen atom is now 180o.

VSEPR Theory e- H2O Lewis Dot Structure H O 104o Water has two bonded hydrogens and two unshared electron pairs on the central atom. The two hydrogen atoms are also repelled by the two lone pairs on the central atom, which give the molecule a bent shape. The bond angle between each hydrogen atom is now 104o.

VSEPR Theory B F Lewis Dot structure for boron trifluoride: Each fluorine bonded to the central boron is positioned as far apart from each other as possible, giving the boron trifluoride molecule a trigonal planar shape. The bond angle between each fluorine atom is now 120o.

VSEPR Theory Lewis Dot structure for CH4 Each hydrogen bonded to the central carbon is positioned as far apart from each other as possible, giving the methane molecule a tetrahedral shape. The bond angle between each hydrogen atom is now 109.5o.

Molecular Geometry The molecular geometry of a molecule is determined by the number of bonded atoms and lone pairs of electrons around the central atom of that molecule. The molecular shape of a molecule can be predicted if the number of bonded atoms and lone pairs of electrons around the central atom is known.

Molecular Geometry 2 Linear 180o # of bonded atoms # of lone pairs
(central atom) Molecular Geometry Molecule Bond Angles 2 Linear 180o

Molecular Geometry 2 1 Bent 109o # of bonded atoms # of lone pairs
(cent. atom) Molecular Geometry Molecule Bond Angles 2 1 Bent 109o

Molecular Geometry 2 Bent <109o typically 104o # of bonded atoms
# of lone pairs (cent. atom) Molecular Geometry Molecule Bond Angles 2 Bent <109o typically 104o

Molecular Geometry 3 Trigonal Planar 120o # of bonded atoms
# of lone pairs (cent. atom) Molecular Geometry Molecule Bond Angles 3 Trigonal Planar 120o

Molecular Geometry 4 109.5o Tetrahedral # of bonded atoms
# of lone pairs (cent. atom) Molecular Geometry Molecule Bond Angles 4 Tetrahedral 109.5o

Objective to predict the molecular shape for molecules using Valence Shell Electron Pair Repulsion (VSEPR) theory. shapes to know: linear bent trigonal planar tetrahedral