MediumChemistryHigh School (11–12)Chemical Bonding › Shapes of Molecules and HybridisationConceptual
Predict the shapes of the ammonium ion NH₄⁺, the hydronium ion H₃O⁺ and the amide ion NH₂⁻.
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Predict the shapes of the ammonium ion , the hydronium ion and the amide ion . Nitrogen has outer electrons and oxygen . Remember to allow for the charge.
Need a reminder? The key ideaShow
VSEPR theory: count the electron pairs on the central atom as . Here is its outer electrons, its singly bonded atoms and the charge, added for an anion. Pairs spread out: 2 linear, 3 trigonal planar, 4 tetrahedral, 5 trigonal bipyramidal, 6 octahedral. Lone pairs repel more than bonding pairs. The shape names only the positions of the atoms. With five pairs, lone pairs take equatorial positions.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. . pairs, all bonding, so lone pairs: tetrahedral, like methane.
Step 2. . pairs, three bonding, one lone pair: trigonal pyramidal, like ammonia.
Step 3. . pairs, two bonding, two lone pairs: bent, like water.
Answer: tetrahedral, trigonal pyramidal and bent.
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