CHAPTER 13
MOLECULAR STRUCTURE

13-1 Electron Distribution Outer electron pairs attracted by 2 nuclei are called shared pairs. Outer electron paris that are not involved in bonding are called unshared pairs Lewis electron dot shows outer shell around the symbol as paired dots/max of 4 pairs of 2=8e-

13-2 Electron Pair Repulsion at one time the electron-pair repulsion theory was called valence shell electron pair repulsion theory/term outer energy level is now used instead of valence shell electron pairs spread as far apart as possible to minimize repulsions electron pair repulsions in a molecule may not be equal the shape of a molecule can be predicted by taking into account the mutual repulsion of electron pairs due to the same electrostatic charge and the pauli exclusion principle. the shape of a molecule containing 3 or more atoms is determined by the number and type of electron clouds in the outer level

13-3 Hybrid Orbitals s(1)p(1,1,1)/s is single instead of double/mainly carbon with 4eŠ in last shell/combine to form 4 tetrahedral sp(3) orbitals 1 s and 2 p orbitals merge to form 3 planar sp(2) hybrid orbitals 1 s and 1 p orbital merge to form 2 linear sp hybrid orbitals the actual bond angles may vary from the predicted angles/ unshared electron pairs occupy the most space/shared pairs occupy the least space

13-4 Geometry of Carbon Compounds

13-5 Sigma and Pi bonds a sigma bond can be formed by these orbitals overlapping 2 s orbitals s & p orbitals 2 p orbitals 2 hybrid orbitals hybrid orbital and s orbital If 2 p orbitals overlap sideways(parallel), they form a pi bond in a double bond 2 pairs of electrons are shared between the bonding atoms/consists of 1 sigma and one pi bond in a triple bond 3 pairs of electrons are shared between the bonding atoms/one sigma and 2 pi bonds double and triple bonds are less flexible but stronger than single bonds compounds that contain double and triple bonds between carbon\ atoms are unsaturated compounds

13-6 Organic Names compounds containing carbon with single bonds between them are called saturated. Œall single bonds end in -ane double bond end in -ene triple bond end in -yne # carbon atoms total names start with 1-meth 2-eth 3-pro 4-but 5-pent 6-hex 7-hept 8-oct cyclic compounds may be represented using skeletal outlines with double and triple lines representing bonds

13-7 Multiple bond Molecular Shapes a double bond consists of 4 e- occupying the space between bonded atoms a triple bond consists of 6 electrons occupying the space between bonded atoms some compounds can contain more than eight electrons in their outer level/study of expanded octet is important in the study of complex ions(chap 14)

13-8 Benzene benzene ring results form the overlap of 6 sp(2) hybrid carbon atoms/the unhybridized p orbitals form 2 pi clouds allowing electrons to be shared around the ring the delocalization of pi electrons among the carbon atoms in benzene results in greater stability in the compound conjugated systems can occur in chains or rings of atoms

13-9 Isomers isomers have the same molecular formula but different structures a double bond prevents free rotation of the atoms on each end of the bond cis and trans are the 2 forms of geometric isomers cis:like atoms or groups are on the same side of the double bond trans:like atoms or groups are on the opposite sides of the double bond positional isomers are formed in hydrocarbon molecules where new particles can occupy 2 or more different positions functional isomers are formed when a new element can be bonded in 2 or more different ways the mass spectrometer can be used to distinguish between isomers that have very similar properties

13-10 Inorganic compounds atoms of elements other than carbon may have hybridized orbitals

13-11 Bond summary chemists use different theories to explain molecular structures two of these theories are: electron pair theory/& hybrid orbital theory