Ch 3 Shapes and Polarity of Chemical Species Flashcards
why is shape important???? huh??
molecular shape accounts for many of the macroscopic properties of real world objects
What does VSEPR stand for
Valence-Shell Electron-Pair Repulsion theory
What elements does VSEPR specifically apply to
p-block elements (ex ), C, N, B, P
What is VSEPR based on?
Coulombic (electrostatic) repulsion between bonding and non-bonding electron pairs, all oriented as far away as possible from each other
minimizes new electrostatic repulsion, which minimizes overall energy of the molecule
perspective diagram
shows 3D structure of a molecule in 2D space
steps to determine molecular shape
- draw the best lewis structure
- sum # lone pairs (E) and # of atoms bonded to the central atom (X), add these up to determine parent shape
axial and equatorial
equatorial like the equator and axial right from pole to pole
rule double bonds?
two molecules attached by double bond, attached electron pairs/bonds always on the same plane
what does “shape” on it’s own refer to?
molecular geometry (distinct from parent shape)
to remember, questions with -OH etc
sometimes don’t need to draw parts of perspective, important to pay attention to what is being asked. OH and CH3 are often condensed
determining shape of molecules with more than 1 central atom
determine individual molecular shape, then how to connect keeping in mind rules of double bond, same plane etc
procedure for determining molecular polarity
- determine molecular shape, draw perspective diagram
- draw bond dipoles for all bonds, direction and relative magnitude
- sum dipole vectors, may have to draw out the different planes etc.
whats alwasy on a terminal arm??
hydrogen, fluorine
4 terminal arms, two of each element?
probably arranged opposite each other, alternating to balance electronegativities
what is 2, 4
SQUARE PLANAR, not see saw, see saw is 1, 4 from trigonal pyramidal parents shape, square planar is from octahedral
