01:160:161 Study Guide - Midterm Guide: Lone Pair, Formal Charge, Chemical Formula
29 Nov 2015
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Exam 2, 2011 worked out solutions: ch4, nh3, and h2o all have 4 pairs of electrons around the central atom. Ch4 has 4 bonds; nh3 had 3 bonds, 1 lone pair; h2o has 2 bonds, 2lone pairs. This means that the electron-domain geometry is tetrahedral in all of these molecules. Lone pairs spread out more and there is more repulsion between lone pair-bonded pair than between bonded-pair to bonded-pair. The presence of lone pairs pushes the bonds a little closer to each other, resulting in a smaller bond angle. Ch4 with 4 equivalent bonds pointing to the corners of a tetrahedron has the ideal tetrahedral angle of 109. 5o. Nh3, with 3 bonds and 1 lone pair has a bond angle of 107o. H2o, with 2 bonds and 2 lone pairs, has a bond angle of 104. 5o. Choice d: the structure of sulfate ion, so4.
