BondingBonding

Day 3Day 3

Please answer the following on Please answer the following on your own piece of paperyour own piece of paper

1.1. Draw the Lewis structure for:Draw the Lewis structure for:A.A. CaICaI22

B.B. OClOCl22

2.2. Indicate whether the compounds in Indicate whether the compounds in number 1 are ionic or covalent and number 1 are ionic or covalent and describe what is happening with the describe what is happening with the electrons in the compounds (who is electrons in the compounds (who is giving, who is taking and who is sharing).giving, who is taking and who is sharing).

Bond Strength and LengthBond Strength and Length

Strength, in general:Strength, in general: Triple bonds are stronger than double which are Triple bonds are stronger than double which are

stronger than single.stronger than single. See Table 16.3 on page 448See Table 16.3 on page 448 Usually listed in kJ/molUsually listed in kJ/mol Example CExample C22HH22

Length, in general:Length, in general: Triple bonds are shorter than double which are Triple bonds are shorter than double which are

shorter than single.shorter than single. See Table 16.3 on page 448See Table 16.3 on page 448

ResonanceResonance

Structures which occur when two or more Structures which occur when two or more equally valid Lewis structures can be written for equally valid Lewis structures can be written for the same molecule, yet neither is correct.the same molecule, yet neither is correct.

Example: OExample: O33 (ozone) (ozone)

Since both of these structures imply that one bond Since both of these structures imply that one bond is shorter than the other, neither is correct. is shorter than the other, neither is correct. Actual evidence indicates that both bonds are Actual evidence indicates that both bonds are the same length. Connecting both structures by the same length. Connecting both structures by a double-headed arrow implies that the actual a double-headed arrow implies that the actual structure is a kind of hybrid of the two structure is a kind of hybrid of the two possibilities.possibilities.

Polyatomic IonsPolyatomic Ions

Multiple atoms with a charge.Multiple atoms with a charge.Usually contain covalent bonds.Usually contain covalent bonds.Example: CNExample: CN--

Show brackets and charges to indicate Show brackets and charges to indicate change in electron number.change in electron number.

Coordinate Covalent BondCoordinate Covalent Bond

When both electrons in bond pair come When both electrons in bond pair come from one atom.from one atom.

Example:NHExample:NH44++

Most polyatomic cations and anions Most polyatomic cations and anions contain covalent and coordinate covalent contain covalent and coordinate covalent bonds.bonds.

Can be shown as an arrow in the Can be shown as an arrow in the structural formula pointing away from the structural formula pointing away from the atom where the electrons originated. atom where the electrons originated.

Magnetisms?Magnetisms?Two types in molecules:Two types in molecules:

1.1. DiamagneticDiamagnetic – all electrons are paired – all electrons are paired

slightly repelled by a magnetslightly repelled by a magnet

2.2. ParamagneticParamagnetic – one or more unpaired – one or more unpaired electronselectrons

attracted to a magnetattracted to a magnet

Mass will appear greater in a Mass will appear greater in a magnetic fieldmagnetic field

(both are different from ferromagnetism)(both are different from ferromagnetism)

ExceptionsExceptions

When the octet rule does not When the octet rule does not work.work.

1.1. Molecules with odd # of Molecules with odd # of electronselectrons

NONO

2.2. Some molecules complex with Some molecules complex with others to complete an octetothers to complete an octet

BFBF33NHNH33

3.3. Some have expanded octetsSome have expanded octets

When there are more than an octet and it is When there are more than an octet and it is obvious, turn the dots on the central atom obvious, turn the dots on the central atom into bonds. Then place the lone pairs on into bonds. Then place the lone pairs on

the terminal atoms.the terminal atoms.

PClPCl55 and SF and SF66

(expanded since after the 3(expanded since after the 3rdrd energy level “d” energy level “d” is there)is there)

Overview of ExceptionsOverview of Exceptions

Phosphorus can make 5 bondsPhosphorus can make 5 bondsSulfur can make 6 bondsSulfur can make 6 bondsBoron can make 3 bondsBoron can make 3 bondsBeryllium can make 2 bondsBeryllium can make 2 bonds

Shape TheoryShape TheoryWays to explain the shape of Ways to explain the shape of

molecules.molecules.

Hybridization (Next week’s Hybridization (Next week’s discussion)discussion)

VSEPR Theory (Today and VSEPR Theory (Today and Monday)Monday)

VSEPR TheoryVSEPR Theory Stands for: Valence Shell Electron Stands for: Valence Shell Electron

Pair Repulsion TheoryPair Repulsion Theory

Electron pairs repel each other, Electron pairs repel each other, whether they are in chemical bonds whether they are in chemical bonds (bonding pairs) or unshared (lone (bonding pairs) or unshared (lone pairs).pairs).

Electron pairs assume orientations Electron pairs assume orientations about an atom to minimize repulsionsabout an atom to minimize repulsions

Applying the VSEPR TheoryApplying the VSEPR Theory

1.1. Draw a possible Lewis structure of Draw a possible Lewis structure of the molecule.the molecule.

2.2. Determine the number of bonding Determine the number of bonding pairs and lone pairs on the central pairs and lone pairs on the central atom.atom.

3.3. Find shape on handout and establish Find shape on handout and establish the geometry of the molecule about the geometry of the molecule about the central atom.the central atom.

4.4. If there is more than one central If there is more than one central atom shape is described about all of atom shape is described about all of the central atoms.the central atoms.