CHEM 101 Lecture Notes - Lecture 19: Lone Pair, Steric Number, Lewis Structure

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CHEM 101-Lecture 19-Electron Domain Geometries (Continued)
Steric number 5
See-saw molecules (one lone pair, four bonds)
Lone pair is always found at an equatorial position (not an axial position), in order
to reduce electron repulsion
Bond angles are contracted by lone pair; 101.6° rather than 120° between the
equatorial bonds, and 173.2° rather than 180° between equatorial bonds
Ex: SF4
https://chem.libretexts.org/LibreTexts/Howard_University/General_Chemistry%3A_An_Atoms_First_Approach/Unit_2
%3A__Molecular_Structure/Chapter_6%3A_Molecular_Geometry/Chapter_6.3%3A_VSEPR_-_Molecular_Geometry
T-shaped molecules (two lone pairs, two bonds)
Both lone pairs are found in equatorial positions in order to reduce lone pair
interactions
The angle between the lone pairs is larger if they are in equatorial
positions (120° rather than 90°), so repulsion is minimized
Angles between the remaining equatorial bond and each axial bond are 87.5°
rather than 90°
Ex: BrF3
http://www.cod.edu/people/faculty/jarman/richenda/1551_hons_materials/Molecular%20shapes_1551.pdf
Steric number 6
Square pyramidal molecules (one lone pair, five bonds)
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