12-10 - Carbon Compounds(Organics Organic compounds are...

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Unformatted text preview: Carbon Compounds (Organics) Organic compounds are those containing carbon. - They are many and varied. - _ Carbon is very versatile in' its bonding. - C u C bonds are very strong. Aliphatic Hydrocarbons Hydrocarbons whose bonds are all localized as single. double or triple bonds (no resonance structures possible). Alkenes Alkenes — contain at least one carbon-carbon double bond H \c— r/ / "'" “\ H H (d) Films: irriuylcm) H l n c ‘1‘.“ “a” Ii 1 C Hr \‘fycxfl H . (chlcuzmiu H Hydrocarbons —— contain only carbon and hydrogen. Alkanes —contain only carbon-carbon single bonds Hydrocarbons H—(%— H H (a) Methane HH ll ii—C—Cull l i HH (b) Ethane 1|: H—c E H -H E _C_ l H n E C_ l H (c) Pawn: Alkynes — contain at least one carbon-carbon triple bond Alkanes Alkynes Acetylene, HCECH l l t l l l Aromatic Hydrocarbons Hydrocarbons whose bonding isn't easily described by Lewis structures (resonance structures necessary). Example 4 8.75 In text Identify the class of organic substance for each of the following molecules: (b) Hsc—CHS aim (d) H3C-CH=CH2 MW Shapes of Molecules We will use VSEPR (valence shell electron pair repulsion) theory to help us determine shapes of molecules - electrons around atom (bonding and lone pair) will arrange themselves to be as far apart as possible 130' s m .. I i 3. :C35 893C“ [Cl '“' 86" CE I itnearstmcture .0 I. - ~— - Example: BeCI2 - as far apart as possible h‘nwiihamm- Valence Sheil Electron-Pair Repulsion (VSEPR) Theory VSEPR explains why molecules take the shapes they do. Why is shape important? Medicines, odors, tastes. depend on one (large) molecule recognizing the shape of another. Molecular Shape TABLE 8.5 I Geometric Structures Arising from Diilerent Numbers of Atoms fihi‘éirieiit‘nf' Molecular Shapes In order to describe the shape of a molecule we will use the following quantities: - bond lengths —- distances between atomic nuclei — bond angles — angles between bonds Molecular Shape TAMI-i as: ] ”mat Madman Pain and Makeup: mm IVSEPR: I Central Atoms wlBonding Pairs Only 3 atoms attached to central 1" BH 120° 3 Cat H H to be as far apart as possible. bonding pairs (and ..hydrogens) must be 120' apart Molecular Shape Steps for Predicting Molecular Shape: Draw a Lewis structure. . Count number of atoms bonded to central atom; count number of unshared electron pairs on central atom. . Add two numbers determined from step 2. This indicates the parent structure. Determine molecular shape from parent structure — only consider positions occupied by atoms. VSEPR: Central Atoms wIBonding Pairs Only 2 atoms attached to central 130° CO, :0:=c=:o: to be as far apart as possible. bonding pairs (and ..oxygens) must be 130" apart 20: Ca (9 '6“ (at)? -. U . W) Imam M0 nmlmncG-vs e‘ on C1. VSEPR: Central Atoms wIBonding Pairs Only 4 atoms attached to central 1n9.5° I .-C w *- HH H CH4 to be as far apart as possible. bonding pairs (and Lhydrogens) must be 109.5“ apart FarmL strum: 16mm ' ' ‘ : “fei’mw VSEPR: Bonding & Nonbonding Pairs 3 electron pairs on centrallatom BH3 -— no lone pairs (trlgunal planar) SO; - ono lone pair :o:='s'=:o: :o:=s=za: Lone pair of electrons repels bonding pairs. mi Bonding & Nonbonding Pairs 4 electron pairs on central atom (cont’d) so {-29 H—O—H H H20 - two lone pairs Lone pair of electrons repels bonding pairs. Per swam ; easel/damp .« bank Polar vs. Nonpolar Molecules - a molecule is polar if it - contains polar bonds and polar bonds are not arranged symmetrically around the central atom OR — has lone pairs of electrons (unsymmetrically arranged) on central atom - a molecular is nonpolar if it — contains only nonpolar bonds OR — contains polar bonds that are arranged symmetrically around the central atom with no lone pairs on central atom VSEPR: Bonding & Nonbonding Pairs 4 electron pairs on central atom CH‘ - no lone pairs (tetrahedral) ‘ NH, - one lone pair H Example 5 8.92 in text Predict shapes and give approximate bond angles for the following molecules: (a) 003 (b) FNO (c) FCN (d) HNa (e) PFa (f) 31:2 (9) N02 ...
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