Drill #1 – Jan. 7, 2014 Draw the Lewis Structures for CF4,

NH3, CO2, H20, H2CO and C2H2 on your Hybridization Worksheet.NO2

-1

Objectives SWBAT write Lewis structures for

molecules that are exceptions to the octet rule.

SWBAT explain resonance and write resonance structures.

Apply hybridization to determining the orbital shape of a molecule.

Announcement Wed/Thurs – quiz (~30 pts) Review WS – posted on webpage Turn in STEM redos January 23 – STEM Fair Poster Due

MidTerm Exam Schedule

Tues, 1/14 Full Day – Period 1 Exam during the regular time pd

Wed, 1/15 Day 2 -Examinations – Periods 2 & 3 Schools close 3 hours early.

Thurs, 1/16 Day 3 -Examinations – Periods 4A & 4B Schools close 3 hours early.

Fri, 1/17 Day 4 -Examinations – Periods 5 & 6 Schools close 3 hours early.

Expanded Valence, Resonance & Hybridization

Exceptions to the Octet Rule1) Molecules with an odd # of

electrons2) Molecules in which an atom has

less than an octet of electrons3) Molecules in which an atom has

more than an octet of electrons4) Molecules that only need two

valence electrons to be stable.

Exceptions to the Octet Rule1) Molecules with an odd number of valence

electrons – Example: NO

Exceptions to the Octet Rule2) Less than an

Octet

Exceptions to the Octet Rule

3) More than 8 valence electrons; Occur in atoms that have the 3d sublevel available for bonding

Exceptions to the Octet Rule4) Atoms that only have two valence

electrons H, He, Li, and Be Stable with only two valence

electrons in their s sublevel

“Expanded Valence” Some molecules or ions have an

“expanded valence” where there are more than 8 electrons in the valence shell of an atom (in these cases, bonding involves electrons in the d orbitals as well as in the s and p orbitals)

You know you have expanded valence if the bonding electrons are less than the bonds necessary to connect everything!

Example: XeF4

Expanded Valence: XeF4

Only third-period (or lower) elements are capable of having an expanded valence; second period elements can not exceed the octet

Why??

Practice ProblemsDraw Lewis structures for the

following:

ICl4-

Trigonal BipyramidalFive bonds around a central atom. (will only occur in the case of an expanded octet)Bond angle = 120° & 90°

OctahedralSix bonds around a central atom. (will only occur in the case of an expanded octet)Bond angle = 90°

Less than an Octet Situations where there are fewer

than an octet of electrons around an atom are rare

Boron does not have an octet, only 6 valence electrons

Example: BF3

Lewis Structure for BF3

Resonance Resonance refers to bonding in

molecules or ions that cannot be correctly represented by a single Lewis structure

If two resonance structures exist for a molecule, the “true” structure is best represented by the average of the two resonance hybrids

Example: O3

Resonance Forms of Ozone

Drill #2 1/6 & 7/14 Take out Chemical Bonding: 9:1 Bonding of

Atoms. Determine the type of bond (polar covalent,

nonpolar covalent, ionic) that exists between the following atoms: H and S Mg and F P and Cl I and I

Use old WS for electronegativity values and the following slide for electronegativity ranges.

Bond Type by Electronegativity

Electronegativity Difference

Bond Type

<0.4 nonpolar covalent

Between 0.4 & 1.7 polar covalent

>1.7 ionic

Drill #2 1/6 & 7/14Answers: H and S – nonpolar covalent (~0.38) Mg and F – ionic (~2.67) P and Cl – polar covalent (~0.97) I and I – nonpolar covalent (0.00)

Use old WS for electronegativity values and the following slides for electronegativity ranges.

Objectives Apply hybridization to determining the

orbital shape of a molecule. Organic chemistry intro…

Hybridization

Each atom has their own orbitals (we know orbital diagrams)…BUT when atoms are combined in a molecule, their orbitals combine or OVERLAP to make molecular orbitals

These are orbitals that apply to the entire molecule that hold 2 electrons

Hybridization

What is hybridization? Atoms use their valence electrons to form

bonds. But how is it that they form bonds of equal energy when some of the electrons come from the s orbital and some come from the p orbital??

Hybrid orbitals are orbitals of equal energy (between the energy of s & p orbitals) produced by the combination of two or more orbitals on the same atom.

Hybridization An atom in a molecule may adopt a

different set of atomic orbitals (called hybrid orbitals) than those it has in the free state.

The hybridization of a particular molecule is determined by the central atom. We only need to worry about it’s valence electrons.

Your Hybridization Options: sp sp2

sp3 sp3d sp3d2

sp3d3

Consider CH4

Carbon has 4 valence electrons 1s2 2s2 2p2

2 of the electrons are in the s orbital and 2 are in the p orbital.

s & p have different shapes and different amounts of energy.

Consider CH4

To create 4 equal bonds, carbon’s one 2s orbital and three 2p orbitals fuse into 4 new identical orbitals called sp3.

2s

2p

sp3Hybridization

HybridizationBCl3

Look at BWrite the orbital diagram for BPromote electrons

http://www.dlt.ncssm.edu/tiger/diagrams/moleculargeometry/BCl3_Hybrid.gif

1s2 2s2 2p1

2s

2p

sp2

Hybridization sp3

Empty hybridized orbitals are dropped

So sp3 becomes sp2

What type of hybridization does BF3 have?

What type of hybridization does H2O have?

O 1s2 2s2 2p4

2s

2psp3

Hybridization