CHEM 1A Lecture Notes - Lecture 20: Trigonal Planar Molecular Geometry, Trigonal Pyramidal Molecular Geometry, Vsepr Theory

• School: UCSB
• Department: Chemistry and Biochemistry
• Course: CHEM 1A
• Professor: Bernt

Document Summary

Higher bond order = higher bond energy. Double bond is not twice as strong as single bond. Triple bond is not 3x as strong as single bond. Hrxn tells you the heat flow for a reaction done at constant pressure. H = (bonds broken) (bonds formed) Energy added to break a bond (+) Energy released to form a bond (-) Bonds broken: 2 h h and 1 o=o. [2(432 kj/mol) + 1(495 kj/mol)] 4(467 kj/mol) = -509 kj. Add energy to break bonds - release energy to form bond. Tells you shape, bond angles, and polarity. Lewis structure of methane is a planar molecule with 90 bond angles. Vsepr model, however, is triangular pyramid-shaped with 109. 5 bond angle. Since electrons repel each other, bonds and lone pairs move as far apart as possible. Determine steric number (sn) for central atom: count all atoms and lone pairs attached to central atom.