Solid State Chemistry Chapter 6 Organic Chemistry: Introduction

AGENDA  Soft and Biosolids –Introduction to Organic Chemistry –Acid Base Equilibria –Protein Structure and Function –DNA and RNA –Self Assembly

Elements Essential to Life The energy level diagram for a fluorine atom (1s 2 2s 2 2p 5 ).

Lewis Structures Gilbert N. Lewis Valence shellValence shell: the outermost electron shell of an atom Valence electronsValence electrons: electrons in the valence shell of an atom; these electrons are used in forming chemical bonds and in chemical reaction Lewis structureLewis structure –the symbol of the atom represents the nucleus and all inner shell electrons –dots represent valence electrons Lewis structures for elements 1-18 of the Periodic Table Fluorine atom (1s 2 2s 2 2p 5 ) Inner shell

Lewis Model of Bonding Atoms bond together so that each atom in the bond acquires the electron configuration of the noble gas nearest it in atomic number (He, Ne) – Octet Rule anion –an atom that gains electrons becomes an anion cation –an atom that loses electrons becomes a cation –Ionic bond (to lose or gain –Ionic bond (to lose or gain electrons to fill the valence shell) : a chemical bond resulting from the electrostatic attraction of an anion and a cation –Covalent bond –Covalent bond : a chemical bond resulting from two atoms sharing one or more pairs of electrons to fill the valence shell We classify chemical bonds as ionic, polar covalent, and nonpolar covalent based on the difference in electronegativity between the atoms

Electronegativity ElectronegativityElectronegativity: a measure of the force of an atom’s attraction for the electrons it shares in a chemical bond with another atom Pauling scale –increases from left to right within a period –increases from bottom to top in a group

Drawing Lewis Structures To draw a Lewis structure: –determine the number of valence electrons in the molecule or ion –determine the arrangement of atoms –connect the atoms by single bonds –arrange the remaining electrons so that each atom has a complete valence shell –show bonding electrons as a single bond –show nonbonding electrons as a pair of dots –atoms share 1 pair of electrons in a single bond, 2 pairs in a double bond, and 3 pairs in a triple bond

Drawing Lewis Structures In neutral molecules containing C, H, N, O, and halogen –hydrogen has one bond (2 e - ) –carbon has 4 bonds and no unshared electrons (8 e - ) –nitrogen has 3 bonds and 1 unshared pair of electrons –oxygen has 2 bonds and 2 unshared pairs of electrons –halogen has 1 bond and 3 unshared pairs of electrons

Ionization Energy

Ionic Bonds

Multiple Covalent Bonds

The Octet Rule

Lewis Structures of Ions

Formal Charges

Table of Common Formal Charges

Arrhenius Acids and Bases

Bronsted-Lowry Acids and Bases

Acid and Base Strength

Acid and Base Reactions

Weak Bases

Relationship between Ka and Kb

Ionization of Water and pH

The pH Scale

Acid-Base Equilibrium

Structure and Acidity The most important factor in determining the relati ve acidity of an organic acid is the relative stability of the anion, A -, formed when the acid, HA, transfe rs a proton to a base We consider three factors: –the electronegativity of the atom bonded to H in HA –resonance stabilization of A - –the inductive effect

Electronegativity of the atom bearing the negative charge; within a period –the greater the electronegativity of the atom bearing the negative charge, the more strongly its electrons are held, the more stable the anion A - –and the greater the acidity of the acid HA Structure and Acidity

Resonance delocalization of charge in A - –compare the acidity of an alcohol and a carboxylic acid –carboxylic acids are weak acids; values of pK a for most unsubs tituted carboxylic acids fall within the range of 4 to 5 –alcohols are very weak acids; values of pK a for most alcohols f all within the range of 15 to 18 Structure and Acidity

–the greater the resonance stabilization of the anion, the more a cidic the compound –there is no resonance stabilization in an alkoxide anion –we can write two equivalent contributing structures for the car boxylate anion; the negative charge is spread evenly over the t wo oxygen atoms Structure and Acidity

The inductive effect –the polarization of electron density transmitted through covale nt bonds by a nearby atom of higher electronegativity –the withdrawal of electron density delocalizes the negative charges Structure and Acidity

Lewis Acids and Bases