Geometry of MoleculesSignificance?

Enzymes (metabolic reactions)DrugsEyesightSense of smell

VSEPRValence Shell Electron Pair RepulsionBased on the notion that electron groups will

orient themselves as far away from one another as possible, making bond angles as large as possible.

Water has two lone pairs.This causes a compression of the bond angle to 105.

Water’s bonds are polar andis asymmetrical in shape sothe bond polarities do notcancel. This also makes the watermolecule polar, giving it anet positive charge on one sideand a net negative charge on the other.

The Unusual Properties of Water

Unusually high boiling point

Compared to other compounds in Group 16

Two Types of GeometriesElectron-Pair Geometry – based on the

arrangement of electron groups around the central atom. (multiple bonds treated as one group)

Molecular Geometry – based on the arrangement of atoms bonded to the central atom. (must differentiate between bonding and nonbonding electron groups)

Molecular shape determined by bond angles.

Molecular size determined by bond length

Nonbonding or “lone” pairs spread out more and can cause bond angles to compress. In ammonia,NH3, the electron-pair geometry predicts a bond angleof 109.5 but the lone pair causes a slight compressionof the angle to 107.

Linear (straight line)Ball and stick model

Space filling model EX. CO2

BentBall and stick model

Space filling model

EX. H2O

Trigonal pyramidBall and stick model

Space filling model

EX. NH3

TetrahedralBall and stick model

Space filling model

Ex. CH4

Molecular PolarityMolecules may be polar or nonpolar.Molecules that are polar are said to have a

dipole or possess a dipole moment.Dipole Moment is a value that indicates the

degree of polarity of the molecule.

Carbon dioxide is nonpolar Water is polar

Attractions between moleculesvan der Waals forces

Weak attractive forces between non-polar molecules

Hydrogen “bonding”Strong attraction

between special polar molecules

Intermolecular attractions

Intermolecular Forces of Attraction

Attraction between a hydrogen atom on one molecule and a very electronegative atom on an adjacent molecule. Only occurs whenhydrogen is bonded to F, O, or N. (HF, H2O, NH3)

Force of a attraction between nonpolar molecules caused bythe motions of electrons and instantaneous dipoles.

Forces of attraction between polar molecules.

Forces of attraction between polar molecules and ions.

Dipole-dipole

Ion-dipole

Ion-dipole

Molecules will be polar if:1. There are polar bonds in the molecule.2. The molecule is not symmetrical.*

*If the molecule is symmetrical, the bond polarities will cancel out leaving no net dipole in the molecule. In this case the molecule is nonpolar or does not possess a dipole moment.

Determining type of IFA

Occurs when atomic orbitals mixto form a particular bonding set around a central atom.

2p2

2s2

1s2C

H

H

H

H

Hybrid orbitals

energy

methaneIn methane the carbon is sp3 hybrid.

Sigma overlap occurs on the internuclear axis and between the two bonded atoms.

All single bonds are sigma bonds.

Pi bonds occur when the overlap is on opposite sides of the internuclear axis.

Only regular ‘p’ orbitals can form pi bonds.

Double bonds are 1 sigma and 1 pi bondTriple bonds are 1 sigma and 2 pi bonds

Double bond = one sigma and one pi bond

One sigma and two pi bonds

How many sigma and pi bonds are in these molecules?

2-propanol

Alpha amino acid

Do you know?1. Are the bonds ionic or covalent in the following? (a) KCl (b) ZnS (c) PCl3 (d) Na2O (e) HCl

2. Which of the following bonds would have the most ionic character?(a) F-F (b) F-O (c) F-N (d) F-C

3. How many valence electrons each of the following have? (a) C (b) Si (c) Mg (d) P

4. Which of the following has the greatest lattice energy?

NaF or KCl Why?5. Draw the Lewis structure for SO3

2-. What is its e—

pair geometry, molecular geometry, bond angles, and hybridization of the central atom?