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So I'm studying chemistry and wondering if any of the geometry names in VSEPR, like linear, trigonal planar, square planar, etc., change if you use a double or triple bond instead of single bonds? Are there any examples of such a thing happening? I tried it using a PhET simulation, but couldn't notice any change at all.

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VSEPR theory classifies molecules based on the number of bonding/lone pairs surrounding the central atom to determine approximations in bonding angles. Because the repulsion forces between double and triple bonds are not significantly greater than single bonds, they are treated as single bonds.

Quoted from Wikipedia:

In VSEPR theory, a double bond or triple bond is treated as a single bonding group.

For example, sulfur trioxide & methanal are considered to be 'trigonal planar', and carbon dioxide, beryllium hydride and hydrogen cyanide HCN are considered to be 'linear'.

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  • $\begingroup$ I see so the repulsion is not that different regardless of bond strength, so the molecular geometry remains the same, right? $\endgroup$
    – Apoqlite
    Sep 17 '20 at 2:41
  • $\begingroup$ @Apoqlite I may be a bit wrong in saying that their repulsions are 'not significantly greater' than single bonds (since their effects are noticeable), but the purpose of VSEPR theory is to provide simple and quick estimations to the bonding angles of a molecule, and treating multiple bonds as single bonds maintains that simplicity. In short, although it sacrifices accuracy, it is 'good enough' for the purpose of crude calculations. $\endgroup$
    – NickC64
    Sep 17 '20 at 14:18
  • $\begingroup$ For an explanation on why multiple bonds have greater repulsion forces than single bonds, read this as per one of the related questions. $\endgroup$
    – NickC64
    Sep 17 '20 at 14:27

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