Unit 3 - Lewis Structures and Geometry Combined Notes

Geometries

linear / linear / 180

trigonal planar / trigonal planar / 120

trigonal planar / bent / <120

tetrahedral / tetrahedral / 109.5

tetrahedral / trigonal pyramidal / 107

tetrahedral / bent / 104.5

trigonal bipyramidal / trigonal bipyramidal / 120

trigonal bipyramidal / seesaw / <120 <90

trigonal bipyramidal / t-shaped / <90

trigonal bipyramidal / linear / 180

octahedral / octahedral / 90

octahedral / square pyramidal / <90

octahedral / square planar / 90

Types of Bonding Based on EN Difference Between Bonding Atoms

0.0-0.4 e- are shared equally, covalent bond

0.4-0.2 e- shared unequally, polar covalent bond

>2 atoms stop sharing e-, ionic bond

EN increases across, decreases down

Lewis Structure Guidelines

  1. Count total number of valence e-

    1. add if negative, subtract if positive

  2. Draw skeleton structure.

  • central atom is usually the first atom

  1. Determine number of e- needed to fill octet

  • if e- available = e- needed, distribute e- to fill all octets

  • if e- available < e- needed, then make multiple bonds

  • if e- available > e- needed, distribute available valence e- to fill octets for all atoms and add the extra e- to the central atom and violate octet rule for central atom

Hybridization

4 e- groups sp3

3 e- groups sp2

2 e- groups sp

single bond - one sigma

double bond - 1 sigma 1 pi

triple bond - one sigma 2 pi

pi bonds are weaker than sigma and allow for greater e- mobility

Justifying Whether a Molecule is Polar or Not

symmetric - bond dipoles cancel out, non-polar

asymmetric - bond dipoles don’t cancel out,