CH 221 1st Edition Lecture 4Outline of Last Lecture • Lone Pairs• Methane• Neutral Nitrogen• Oxygen• Bonds and Orbitals• Carbon• Methane• Ethane• EtheneOutline of Current Lecture • Ethane, Ethene, Ethyne• Bonds in:• Ammonium• Water• Bond Strength• Electronegativity• Acids and Bases• Ka and pKaCurrent LectureIII. Bonding in ethyne provides hybridization of an s orbital and a p orbital into two sp orbitals such as in acetylene which has a 180º bond angle. Ethane Ethene Ethyne# atoms carbon is bonded to 4 3 2Hybridization spBond Angle 109.5º 120º 180ºGeometry Tetrahedral Trigonal Planar LinearSingle bond= 1 sigma Double bond= 1 sigma, 1 pi Triple bond= 1 sigma, 2piIV. Bonds in:• Ammonia () – Four orbitals are hybridized forming four hybrid orbitals. Lone pair electrons are in an orbital. • Water () – Similar to except it has two orbitals that each contain a lone pair and two orbitals used to form bonds.V. Bond strengthThe carbon to carbon triple bond is the strongest bond with the shortest length. The carbon to carbon single bond is the weakest bond with the longest length. Bond strengthincreases as bond length decreases. “The shorter the bond, the stronger it is.” Pi bonds are weaker than sigma bonds. VI. Electronegativity increase to the right, and up the periodic table. It is the measure of how much an atom attracts electrons. VII. Acids and BasesAn acid loses a proton, and a base gains it. Acid/base reactions are reversible meaning they are considered equilibrium reactions. When an acid loses a proton, it forms a conjugate base and when a base gains a proton, it forms a conjugate acid. The stronger the acid, the weaker the conjugate base. Acids have different strengths. For example, Hydrochloric acid (HCl) is much stronger than Acetic acid. • The acid dissociation constant (Ka) is a measure of the extent of dissociation of an acid. Ex. HA + + for this reaction the Ka= pKa= -logKapKa < 1 very strong acidpKa= 1-3 moderately strong acidpKa= 3-5 weak acidpKa= 5-15 very weak acidpKa > 15 extremely weak acidStronger acids have larger Ka and smaller pKa
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