EasyChemistryHigh School (11–12)Chemical Bonding › Shapes of Molecules and HybridisationConceptualBoard ExamAPA-LevelIB
Silicon (4 outer electrons), phosphorus (5) and sulphur (6) each form a chloride: SiCl₄, PCl₃ and…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Silicon (4 outer electrons), phosphorus (5) and sulphur (6) each form a chloride: , and . For each, find the number of electron pairs and lone pairs on the central atom, and name the shape.
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, lone pairs: tetrahedral.
Step 2. . pairs, three bonding, lone pair: trigonal pyramidal.
Step 3. . pairs, two bonding, lone pairs: bent.
Answer: all three have four pairs. The shapes are tetrahedral, trigonal pyramidal and bent.
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