MediumChemistryHigh School (11–12)Chemical Bonding › Lewis Structures and Ionic BondsNumericalConceptual
For each molecule, count the electrons around the central atom, and say whether it has an…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
For each molecule, count the electrons around the central atom, and say whether it has an incomplete octet, an odd number of electrons, an expanded octet, or a normal octet: aluminium chloride, ; chlorine dioxide, ; iodine heptafluoride, ; and carbon dioxide.
Need a reminder? The key ideaShow
Lewis structure: count the valence electrons, adding one per negative charge and taking one per positive charge. Join the outer atoms to the central atom and complete their octets. Put the rest on the centre, and make multiple bonds if the centre is short. Formal charge: . Exceptions to the octet rule: incomplete octet, odd electrons, expanded octet.
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. . Three bonds give aluminium 6 electrons: an incomplete octet.
Step 2. . valence electrons. The total is odd: an odd-electron molecule.
Step 3. . Seven bonds give iodine 14 electrons: an expanded octet.
Step 4. . Two double bonds give carbon 8: a normal octet.
Answer: 6 (incomplete), 19 (odd), 14 (expanded), and an octet for .
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