CHEM 2211 1st Edition Lecture 2 Outline of Last Lecture I Molecular Orbital Theory MO II Linear Conservation of Atomic Orbitals LCAO Outline of Current Lecture I II III IV V Br nsted Lowry Acid Base Theory Ka value Factors that affect Ka Conjugate Acids and Bases Resonance Structures Chapter 3 I II III IUPAC Line Angle Structure Alkanes Vocabulary Br nsted Lowry Acid Base Theory Equilibrium Ka value Resonance Structures Depronate Delocalization of electrons pKa IUPAC Hydrogen bonds Line Angle Structure London Dispersion Forces Heteroatoms Electronegativity Alkanes Conjugate Acids and Bases Current Lecture I Br nsted Lowry Acid Base Theory A Acids are defined as anything that releases an H B Bases are defined as H acceptors i They form OH in water II Ka value A Ka values define the likelihood of a chemical to depronate in a specific solvent B The higher the Ka value the stronger the Acid i String Acids are defined as chemicals which readily depronate and have strong conjugate bases C Ka is found using the following equation H 3 O A K a D However since Ka is generally a very very small number we use the pKa instead It is found using the following equation p K a log K a III IV E The lower the pKa number the stronger the Acid Factors that effect pKa A Nature of Group i H O H vs H F pKa 15 5 vs pKa 3 5 ii Because water is held together by hydrogen bonds instead of only London dispersion forces like in hydrofluoric acid the H ion is easier to remove from HF This means HF is a stronger acid than water B Size i Example HI HBr HCl HF ii HI is the strongest Acid because the large size of Iodine and the small size of Hydrogen causes poor orbital overlap This phenomenon is comparable to bonding a marble H with a basketball I C Electronegativity Conjugate Acids and Bases BH A HA B A HA is the acid A is the conjugate base B B is the base BH is conjugate acid C Equilibrium shifts to the side with the lowest pKa value i Example V D The equilibrium shifts to the left because the pKa of the Acid is higher than the pKa of the conjugate Acid This means the conjugate acid is more likely to dissociate in the solution than the Acid Resonance Structures Brief Overview A Resonance is the average of two or more structures which differ only in the placement of electrons B It adds stability to a molecule i Example 1 ii The Resonance structure number 3 is more stable than numbers 1 and 2 because the electrons are shared across the Oxygens iii Example 2 iv As seen by the mechanism above the phenol is more stable because the electrons are shared around the aromatic ring as opposed to staying on one atom This delocalization of electrons makes phenol less likely to react with other molecules Chapter 3 I IUPAC International Union of Pure and Applied Chemistry A Created the nomenclature for organic chemistry i Prefix specifies number of carbons suffix specifies the type of molecule ii KNOW the first thirteen prefixes 1 2 3 4 5 6 7 MethEthPropButPentHexHept 8 Oct9 Non10 Dec11 Undec12 Dodec13 Tridec II Line Angle Structure for drawing molecules A Rules i Lines are bonds ii Vertices and end points are carbons iii The Hydrogens are implicit iv Heteroatoms get Hydrogens drawn in 1 Heteroatom atom other than carbon B Example C Example of Heteroatom III Alkanes suffix ane A Singly bonded carbons B Nonpolar C Held together by London Dispersion Forces D Example
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