Chemistry Review 021511 wo pics

Chemistry Review 021511 wo pics - 1 CHEMISTRY REVIEW Lia M....

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Unformatted text preview: 1 CHEMISTRY REVIEW Lia M. Nightingale, Ph.D. MOLECULARBONDING 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 MOLECULARBONDING Electronegativity how easily an element can accept electrons MOLECULARBONDING In a molecule: Higher electronegativity = e- acceptor Lower electronegativity = e- donator Electronegativity difference ( EN) = Highest # lowest # Ca F F Ca = 1.0 F = 4.0 EN = 3.0 MOLECULARBONDING EN Bond Type 0 0.4 Nonpolar Covalent 0.41 1.7 Polar Covalent 1.8 Ionic Electrons shared equally + - Electrons shared inequally +- Electrons transferred MOLECULARBONDING Nonpolar covalent bonds Hydrophobic C H H H H H = 2.1 C = 2.5 EN = 0.4 2 MOLECULARBONDING Polar covalent bonds Hydrophilic H = 2.1 O = 3.5 EN = 1.4 - O H H + + MOLECULARBONDING Ionic Bonds Electrons transferred from lower electronegative element to higher electronegative element Hydrophilic Na + Cl- Cl Na Na Cl +- INTRA VS. INTER H Cl H Cl Bonding = Intra molecular forces Inter molecular forces (IMF) Also cal ed covalent interactions Much stronger than IMF Also cal ed noncovalent interactions Determines physical properties: boiling point, viscosity, etc. INTERMOLECULAR FORCES 1. London dispersion forces (aka. van der Waals forces) Weakest force Between ALL molecules Only IMF in nonpolar molecules INTERMOLECULAR FORCES 2. Dipole-dipole force Occurs between 2 polar molecules Attraction between positive dipole ( + ) and negative dipole ( - ) of polar molecules Stronger than LDF, but weaker than ion-dipole INTERMOLECULAR FORCES 2. Dipole-dipole force - O H H + + 3 INTERMOLECULAR FORCES 3. Hydrogen bonding Type of dipole-dipole interaction between H & F, O, or N 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. INTERMOLECULAR FORCES 3. Hydrogen bonding O H C C H H H H H + - EN: C = 2.5 H = 2.1 O = 3.5 Pure ethanol solution INTERMOLECULAR FORCES 3. Hydrogen bonding Compounds can be JUST H-bond acceptors H-bond acceptor = double bonded oxygen will accept a H INTERMOLECULAR FORCES H-bonding is responsible for: Holding DNA strands together INTERMOLECULAR FORCES 4. Ion-dipole interactions Between ionic compound and polar molecules + ion is attracted to - - ion is attracted to + Strongest IMF still a lot weaker than covalent or ionic bonds INTERMOLECULAR FORCES 4. Ion-dipole interactions O HH Na + Cl- O H H O H H O H H 4 STRENGTH OF INTRA & IMF Strength EX. PURE METHANOL SOLUTION O H H C H H EN: C = 2.5 H = 2.1 O = 3.5 EX. PURE ETHANE SOLUTION C H H C H H EN: C = 2.5 H = 2.1 H H EX. PURE LITHIUM FLUORIDE SOLID Li F EN: Li = 1.0Li = 1....
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This note was uploaded on 01/07/2012 for the course PHCH 51311 taught by Professor Nightingale during the Summer '11 term at Palmer Chiropractic.

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Chemistry Review 021511 wo pics - 1 CHEMISTRY REVIEW Lia M....

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