Chemistry Review 093009 wo pics 2 sld

Chemistry Review 093009 wo pics 2 sld - CHEMISTRY REVIEW...

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1 C HEMISTRY R EVIEW Lia M. Nightingale, Ph.D. M OLECULAR B ONDING Based on valence electrons and electronegativity Valence electrons e - in outermost shell Ca F F F Ca + Bonded pair Unshared pair Unpaired e - Ca F F Ca F F OR
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2 M OLECULAR B ONDING Electronegativity how easily an element can accept electrons M OLECULAR B ONDING In a molecule: Higher electronegativity = e - acceptor Lower electronegativity = e - donator Electronegativity difference ( Δ EN) = Highest # lowest # Ca F F Ca = 1.0 F = 4.0 ΔEN = 3.0
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3 M OLECULAR B ONDING Δ EN Bond Type 0 0.4 Nonpolar Covalent 0.41 1.7 Polar Covalent 1.8 Ionic Electrons shared equally δ+ δ- Electrons shared inequally + - Electrons transferred M OLECULAR B ONDING Nonpolar covalent bonds Hydrophobic C H H H H H = 2.1 C = 2.5 ΔEN = 0.4
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4 M OLECULAR B ONDING Polar covalent bonds Hydrophilic H = 2.1 O = 3.5 ΔEN = 1.4 δ- O H H δ+ δ+ M OLECULAR B ONDING Ionic Bonds Electrons transferred from lower electronegative element to higher electronegative element Hydrophilic Na + Cl - Cl Na Na Cl + -
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5 I NTRA VS . I NTER H – Cl H – Cl Bonding = Intra molecular forces Inter molecular forces (IMF) Also called covalent interactions Much stronger than IMF Also called noncovalent interactions Determines physical properties: boiling point, viscosity, etc. I NTERMOLECULAR F ORCES 1. London dispersion forces (aka. van der Waal’s forces) Weakest force Between ALL molecules Only IMF in nonpolar molecules
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6 I NTERMOLECULAR F ORCES 2. Dipole-dipole force Occurs between 2 polar molecules Attraction between positive dipole ( δ + ) and negative dipole ( δ - ) of polar molecules Stronger than LDF, but weaker than ion-dipole I NTERMOLECULAR F ORCES 2. Dipole-dipole force δ- O H H δ+ δ+
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7 I NTERMOLECULAR F ORCES 3. Hydrogen bonding 1. H must be bonded to FON (H-bond donor) AND 2. FON must contain an unshared pair of electrons (H-bond acceptor) H-bonds are only 2-5% as strong as ionic bonds. I NTERMOLECULAR F ORCES 3. Hydrogen bonding O H C C H H H H H δ+ δ- EN: C = 2.5 H = 2.1 O = 3.5 Pure ethanol solution
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8 I NTERMOLECULAR F ORCES 3. Hydrogen bonding Compounds can be JUST H-bond acceptors H-bond acceptor = double bonded oxygen will accept a H I NTERMOLECULAR F ORCES H-bonding is responsible for: Holding DNA strands together
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