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.