Chem 121 1st Edition Lecture 14 Outline of Last LectureI. Chemical BondingII. Bond LengthIII. Bond EnergyIV. Bond OrderV. Electronegativity (EN)VI. Bond Polarity and Dipole MomentVII. Lewis Structures Outline of Current Lecture I. ResonanceII. Lewis Structures of Polyatomic Ions- ProceduresIII. Formal ChargeIV. Exceptions to the Octet Rule Current LectureResonance- Resonance Forms (Structures): True Lewis Structures with a different arrangement of electrons (multiple bonds)- Actual Molecule:o Combination of resonance formso Each resonance can have different weight- Notation:o Lay out/ Write out all resonance forms and connect them with double arrowsLewis Structures of Polyatomic Ions- Procedures- Calculate the total number of valence electronsThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.o Sum the valence electrons of each atom and the electrical chargeo Electrical charge: add one electron for each negative charge and subtract one electron for each positive charge- Set atomso Central atom: Least EN atom, except Ho Surrounding (terminal) atoms: rest of the atom- Distribute electronso One bonding pair between each pair of atomso Rest of electrons First- surrounding atoms: Octet Second- Central atom- Octet for central atomo If not, form a double or triple bond with terminal atoms Move lone electron pairs All the resonance formso Bracket structures with charge in upper right corner- Central Atomso Least EN atom, except Ho Subscript: number of central atomso Oxyacids: H attaches to Oo F and H cannot be central atomsFormal Charge (FC)- FC is the charge an atom would have if the bonding electrons were shared equallyo Select the most acceptable resonance structure- Determine the FCo FC of an atom = (Group #) – (# bonds) – (# electrons in lone pair)- Choose the most acceptable resonance structureo Smaller overall ABSOLUTE VALUE OF FC are preferred Zero charge is most preferred, the more 0’s the better No more than +2 or -2 charges on one atomo Atom with more EN should have a negative chargeo Atoms in period 2 must only have octeto Atoms in period 3 or lower could have >8 valence electronso Avoid like/same charges (++ or - -) on adjacent atomso FC of O (Oxygen): (single bond)O --- -1; (double bond)O --- 0; (triple bond)O --- +1Exceptions to the Octet Rule (3)- Expanded Octet: Central atom- elements in 3rd row or below- Incomplete Octet: Compounds containing B- Free- radical incomplete