Chp 1—Covalent bonding & shapes of molecules

belief that organic compounds must come from a living source

Wohler - 1828 - synthesized urea

2n2 n = shell #

orbitals s — 1/shell p — 3/shell 2+ d — 5/shell 3+

Aufbau principle Pauli exclusion principle Hund’s rule

lower energy orbitals are filled first

only 2 electrons per orbital, and they must spin on their axes in opposite directions

in orbitals of equal energy level, each is singly occupied before any is doubly occupied

electronegativity

ionic: >1.9 difference in EN polar: 0.5-1.9 difference in EN nonpolar: <0.5 difference in EN

N with 3 single bonds and 1 lone pair

O with 2 single bonds and 2 lone pairs

Cl with 1 single bond and 3 lone pairs

• 3rd row elements (from either side) - have d orbitals • small atoms - ex boron forms 3 single bonds

FC = # VE in neutral unbonded atom - (all unshared electrons + ½ of shared electrons)

atoms’ electrons in molecule < VE in unbonded atom

atoms’ electrons in molecule > VE in unbonded atom

0

𝝅 bonds

• only electrons move, not atoms • obey rules of covalent bonding; 3rd period atoms may have up to 12 electrons in shells • keep track of lone pairs & formal charges; all structures must have same number of paired and unpaired electrons • use curved arrows to interconvert & ID structures • use double headed arrow between structures

energy of the true hybrid is << the energy of any contributing structure

degenerate

sigma bonds (𝝈) pi bonds (𝝅)

s + s s + p px + px