In vsepr theory we dont consider double bonds. So why does the structure of SO2 have double bonds ?

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According to VSEPR theory, the shape of the SO2 - its electron and molecular geometries - molecule can be determined by calculating S 's steric and coordination numbers. The steric number (SN) represents the number of bonds that respective atom forms with other atoms (single, double and triple bonds all count as 1) added to the number of lone electron pairs it has. The coordination number (CN) represents the number of other atoms to which the analyzed atom is connected. So, looking at SO2 's Lewis structure (any of the three resonance structures will do), we can see that the Satom's SN=3 (2 bonds with oxygen + 1 lone pair) and its CN=2 (2 bonds with 2 oxugen atoms). This means that the SO2 molecule's electron geometry (taking into consideration lone pairs) is trigonal planar, while its molecular geometry (without taking into consideration lone pairs) is bent. This is where the lone pair of electrons on the S atom makes a difference. SInce electrons are repelled by eachother, the electron pair will determine a bond angle of less than 120∘, what we would see in the case of linear molecular and electron geometries. So, S's lone pair of electrons influences SO2 's molecular geometry.
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