HardChemistryHigh School (11–12)Chemical Bonding › Shapes of Molecules and HybridisationConceptualBoard ExamAPA-LevelIB
Chlorine has 7 outer electrons. Find the electron pairs and lone pairs on chlorine in ClF₃…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Chlorine has outer electrons. Find the electron pairs and lone pairs on chlorine in . In a trigonal bipyramid, how many neighbours at does an axial position have, and how many does an equatorial one have? Use this to explain where the lone pairs go and why the molecule is T-shaped.
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
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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. pairs, three bonding, so lone pairs.
Step 2. Neighbours. An axial pair has all three equatorial pairs at . An equatorial pair has only the two axial pairs at ; its other neighbours are at .
Step 3. The lone pairs. Lone pairs repel the most, so they take the less crowded equatorial positions. Two equatorial corners hold lone pairs.
Step 4. The shape. The fluorines sit in the two axial positions and the last equatorial one. Seen from the side, they make a T. The lone pairs push the axial fluorines back a little, so the angles are slightly under .
Answer: 5 pairs, 2 lone pairs, both equatorial, leaving a T-shaped molecule.
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