A student counts the electrons around the central atom in some molecules, including the electrons…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A student counts the electrons around the central atom in some molecules, including the electrons in lone pairs and in bonds, with each bond pair counted once as two electrons. The species are (2 bonds and 3 lone pairs) and (4 bonds and 2 lone pairs). Next come (6 bonds and 1 lone pair) and (7 bonds). The last is (2 bonds and 3 lone pairs on the central iodine atom). Find the number of electrons around the central atom in each case. Then say which of these species keeps the octet of the central atom.
Need a reminder? The key ideaShow
For the central atom, lone pairs , and the steric number is the number of bonded atoms plus the lone pairs. In a trigonal bipyramid a lone pair prefers an equatorial place, where it has fewer neighbours at 90°. The order of repulsion is lone pair-lone pair, then lone pair-bond pair, then bond pair-bond pair.
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. Count the pairs and multiply by 2.
Step 2. . .
Step 3. . .
Step 4. . .
Step 5. . .
Step 6. . .
Answer: 10, 12, 14, 14 and 10. None of the species keeps the octet. All of them have an expanded octet, which is possible because the central atoms are in the third period or below.
Check. In each case the number is the steric number.
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