Bonding Unit Learning Goal #4: Relate the properties of simple compounds to the types of bonding, shape of molecules, and intermolecular forces.
Jan 17, 2016
Bonding Unit
Learning Goal #4: Relate the properties of simple compounds to the types of bonding, shape of molecules, and intermolecular forces.
MOLECULAR MOLECULAR GEOMETRYGEOMETRY
MOLECULAR MOLECULAR GEOMETRYGEOMETRY
VSEPRVSEPR • VValence alence SShell hell EElectron lectron
PPair air RRepulsion theory.epulsion theory.• Most important factor in Most important factor in
determining geometry is determining geometry is relative relative repulsion between repulsion between electron pairs.electron pairs.
Molecule adopts the Molecule adopts the shape that minimizes shape that minimizes the electron pair the electron pair repulsions.repulsions.
Molecule adopts the Molecule adopts the shape that minimizes shape that minimizes the electron pair the electron pair repulsions.repulsions.
MOLECULAR GEOMETRYMOLECULAR GEOMETRYMOLECULAR GEOMETRYMOLECULAR GEOMETRY
Some Common Some Common GeometriesGeometriesLineaLinea
rr
Trigonal PlanarTrigonal Planar
TetrahedralTetrahedral
VSEPR chartsVSEPR charts
• Use the Lewis structure to determine the Use the Lewis structure to determine the geometry of the moleculegeometry of the molecule
• Electron arrangement establishes the bond Electron arrangement establishes the bond anglesangles
• Molecule takes the shape of that portion of Molecule takes the shape of that portion of the electron arrangementthe electron arrangement
• Charts look at the CENTRAL atom for all Charts look at the CENTRAL atom for all data!data!
Structure Determination Structure Determination by VSEPRby VSEPR
Structure Determination Structure Determination by VSEPRby VSEPR
Water, HWater, H22OO
The electron pair The electron pair geometry is geometry is TETRAHEDRALTETRAHEDRAL
The electron pair The electron pair geometry is geometry is TETRAHEDRALTETRAHEDRAL
The molecular The molecular geometry is geometry is BENTBENT..The molecular The molecular geometry is geometry is BENTBENT..
H O H••
••
H O H••
••
2 bond pairs2 bond pairs
2 lone pairs2 lone pairs
1. Two pairs of electron on a central atom in a molecule are always placed 180o apart (linear).
2. Three pairs of electrons on a central atom in a molecule are always placed 120o apart on the same plane as the central atom (trigonal Planar).
3. Four pairs of electrons on a central atom in a molecule are always placed 109.5o apart (tetrahedral).
4. When every pair of electrons on the central atom is shared with another atom, the molecular structure has the same name as the arrangement of the electron pairs.
Number of Pairs Name of Arrangement
2 Linear
3 Trigonal Planar
4 tetrahedral
5. When one or more of the electron pairs around a central atom are lone pairs, the name for the molecular structure is different from the arrangement of electron pairs.
IntermoleculIntermolecular Forcesar Forces
Intermolecular ForcesIntermolecular Forces
Dipole-dipole Dipole-dipole attraction attraction
Hydrogen bonds Hydrogen bonds Dispersion forcesDispersion forces
Forces of attraction between different molecules rather than bonding forces within the same molecule.
Forces and Phases of Forces and Phases of MatterMatter
o Substances with very little Substances with very little intermolecular attraction exist as intermolecular attraction exist as
gasesgases
o Substances with strong Substances with strong intermolecular attraction exist as intermolecular attraction exist as
liquidsliquids
o Substances with Substances with very strongvery strong intermolecular (or ionic) attraction intermolecular (or ionic) attraction
exist as exist as solidssolids
1. Hydrogen Bond (strongest)
11.2
The hydrogen bond is a special dipole-dipole interaction between the hydrogen atom in a polar N-H, O-H, or F-H bond and an electronegative O, N, or F atom. IT IS NOT A BOND.
A H … B A H … Aor
A & B are N, O, or F
- water is a polar molecule because oxygen is more electronegative than hydrogen, and therefore electrons are pulled closer to oxygen.
2. Ion-Dipole Forces
Attractive forces between an ion and a polar molecule
11.2
Ion-Dipole Interaction
11.2
3. Dipole-Dipole Forces
Attractive forces between polar molecules
Orientation of Polar Molecules in a Solid
11.2
4. Dispersion Forces – van der Walls forces/London forces (weakest)
Attractive forces that arise as a result of temporary dipoles induced in atoms or molecules
11.2
ion-induced dipole interaction
dipole-induced dipole interaction
IntermolecularForces
Formed by theattraction between …
Examples
Ion-dipole an ion and a polar molecule
Na+ and H2O
Hydrogen bond molecules which have H on N, O, or F atoms
H2O and H2O; H2Oand CH3CH2OH
Dipole - Dipole two polar molecules CH3Br and ICl;CH3Br and H2O
Ion - Induced dipole an ion and a nonpolar
Fe2+ and O2
Dipole - Induceddipole
a polar molecule and anonpolar molecule
HCl and Cl2
London (dispersion)forces
two nonpolarmolecules
CH4 and CH4; F2 and F2; CH4 and F2
Summary: Intermolecular Forces
Essential Questions1. What physical properties are
displayed in substances with the various different types of bonds(intermolecular forces)?
2. Build models for water, ammonia, and methane and describe the three-dimensional shape and resulting polarity.