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 Fri, 1/17 Day 4 -Examinations – Periods 5 & 6

Expanded Valence, Resonance & Hybridization

Exceptions to the Octet Rule 1) Molecules with an odd # of electrons 2) Molecules in which an atom has less than an octet of electrons 3) Molecules in which an atom has more than an octet of electrons 4) Molecules that only need two valence electrons to be stable.

Exceptions to the Octet Rule 1) Molecules with an odd number of valence electrons – Example: NO

Exceptions to the Octet Rule 2) 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 Rule 4) 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 Problems Draw Lewis structures for the following: ICl4-

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

Octahedral Six 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 & 7/14 Answers: 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

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

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. 2p Hybridization sp3 2s

Hybridization BCl3 Look at B Write the orbital diagram for B Promote electrons

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

What type of hybridization does BF3 have? 1s2 2s2 2p1 sp3 Empty hybridized orbitals are dropped So sp3 becomes sp2 2p Hybridization 2s sp2

What type of hybridization does H2O have? O  1s2 2s2 2p4 2p Hybridization sp3 2s