octahedral
generic formula: AX6
example: sulfur hexafluoride SF6
If there are no lone pairs then the molecular geometry matches the electronic and is octahedral. The base bond angles are 180° and 90°. There is no reason to tweak the bonds to other values.
POLARITY: NON-POLAR - As long as all six positions are the same, then the molecule cannot be polar due to perfect symmetry. Also, as long as identical atoms are opposite each other (180°) even mixed peripheral atoms can still be non-polar.
square pyramid
generic formula: AX5E
example: iodine pentabromide IBr5
With one lone pair on this electronic geometry, the molecular geometry is now square pyramid. The base angles are still 180° and 90° while the tweaked angle will now be slightly less (179-178° and 89-88°) due to the extra repulsing power of the lone pair.
POLARITY: POLAR - The lone pair electrons throw off the perfectly cancelling symmetry of the six octahedral regions thus making the overall molecule polar.
square planar
generic formula: AX4E2
example: xenon tetrafluoride XeF4
The two lone pairs on this electronic geometry have to be 180° apart which forces the molecular geometry to be square planar. The base angles are 180° and 90°. There is no tweaking the angles on this geometry because the lone pairs are opposite and the whole molecule maintains a perfectly symmetric overall geometry where all localized polarities cancel out.
POLARITY: NON-POLAR - As stated above, the whole molecule has a perfect symmetry and therefore non-polar (assuming equivalent atoms in the peripheral positions).
T-shaped
generic formula: AX3E3 (hypothetical)
example: no real compounds
In theory, if a compound did exist like this, there would be three lone pairs on this electronic geometry, and the molecular geometry would be T-shaped. No known compounds do this however, so the only "real" T-shaped molecules have trigonal bipyramid electroni geometries and not octahedral.
POLARITY: POLAR - For the sake of "thinking like a chemist" the three sets of lone pair electrons would throw off the perfectly cancelling symmetry of the six octahedral regions thus making the overall molecule polar.
linear
generic formula: AX2E4 (hypothetical)
example: no real compounds
Just like T-shaped in this category, no known compounds exist. In theory, if there were four lone pairs on this electronic geometry they would be in a planar arrangement which would leave the molecular geometry to be perfectly linear.
POLARITY: NON-POLAR - If this did exist, the whole molecule has a perfect symmetry and therefore non-polar (assuming equivalent atoms in the two peripheral positions).