1. Section 4: Molecular Shapes
The VSEPR model is used to determine molecular shape. K
What I Know W
What I Want to Find Out L
What I Learned

2. 7(E) Predict molecular structure for molecules with linear, trigonal planar, or tetrahedral electron pair geometries using Valence Shell Electron Pair Repulsion (VSEPR) theory.
7(B) Write the chemical formulas of common polyatomic ions, ionic compounds containing main group or transition metals, covalent compounds, acids, and bases.
7(C) Construct electron dot formulas to illustrate ionic and covalent bonds.
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Molecular Shapes

3. Essential Questions What is the VSEPR bonding theory?
How can you use the VSEPR model to predict the shape of, and the bond angles in, a molecule?
What is hybridization?
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Molecular Shapes

4. Vocabulary Review New atomic orbital VSEPR model hybridization
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Molecular Shapes

5. VSEPR Model
The shape of a molecule determines many of its physical and chemical properties. Molecular geometry (shape) can be determined with the Valence Shell Electron Pair Repulsion model, or VSEPR model which minimizes the repulsion of shared and unshared atoms around the central atom.
Electron pairs repel each other and cause molecules to be in fixed positions relative to each other.
Unshared electron pairs also determine the shape of a molecule.
Electron pairs are located in a molecule as far apart as they can be.
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Molecular Shapes

6. Hybridization
Hybridization is a process in which atomic orbitals mix and form new, identical hybrid orbitals. Carbon often undergoes hybridization, which forms an sp3 orbital formed from one s orbital and three p orbitals. Lone pairs also occupy hybrid orbitals.
Single, double, and triple bonds occupy only one hybrid orbital (CO2 with two double bonds forms an sp hybrid orbital).
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Molecular Shapes

7. Find the Shape of a Molecule
Use with Example Problem 7.
Problem
Phosphorus trihydride, a colorless gas, is produced when organic materials, such as fish flesh, rot. What is the shape of a phosphorus trihydride molecule? Predict the bond angle and identify hybrid orbitals.
SOLVE FOR THE UNKNOWN
Find the total number of valence electrons and the number of electron pairs.
1 P atom × 5 valence electrons 1 P atom + 3 H atoms × 1 valence electron 1 F atom = 8 valence electrons
Determine the total number of bonding pairs.
8 electrons 2 electrons/pair =4 pairs
Response
ANALYZE THE PROBLEM
A phosphorus trihydride molecule has three hydrogen atoms bonded to a central phosphorus atom.
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Molecular Shapes

8. Find the Shape of a Molecule
SOLVE FOR THE UNKNOWN
Draw the Lewis structure, using one pair of electrons to bond each H atom to the central P atom and assigning the lone pair to the P atom.
The molecular shape is trigonal pyramidal with a predicted 107° bond angle and sp3 hybrid orbitals.
EVALUATE THE ANSWER
All electron pairs are used and each atom has a stable electron configuration.
Molecular Shapes
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9. Review Essential Questions Vocabulary
What is the VSEPR bonding theory?
How can you use the VSEPR model to predict the shape of, and the bond angles in, a molecule?
What is hybridization?
Vocabulary
VSEPR model
hybridization
Molecular Shapes
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