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My explanation is, the shape of $\ce{XeF2}$ is actually trigonal bi-pyramidal, but as the 3 lone pairs of $\ce{Xe}$ remain so close to the $\ce{Xe}$ atom itself, it seems that $\ce{XeF2}$ has a linear shape.

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Similarly, $\ce{NH3}$'s shape is trigonal pyramidal instead of tetrahedral as the lone pair resides so close to the nitrogen atom itself.

Is my reasoning accurate?

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    $\begingroup$ Welcome to Chemistry and VSEPR theory.. what you say is accurate enough from that model.. $\endgroup$ Jun 25 at 6:24
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    $\begingroup$ Lone pairs of Xe are as good as any other lone pairs. Forget the exotic stuff. Start with the basics. What is the shape of H2O? Would you call it tetrahedral or otherwise? $\endgroup$ Jun 25 at 8:22
  • $\begingroup$ @IvanNeretin Great example, I get it now. Even though $H_20$ has an sp3 hybridization, its shape is bent/angular not tetrahedral, which is commonly associated with molecules having sp3 hybridization. $\endgroup$ Jun 25 at 8:27
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    $\begingroup$ I would not even call that "not tetrahedral". It is tetrahedral all right, but in a different sense. Imagine a short-sighted man who only sees big solid things, like atoms. He looks at $\ce{H2O}$ and calls it bent. Then he puts his glasses on, so now he can see electron pairs as well. He looks at $\ce{H2O}$ again and calls it tetrahedral. $\endgroup$ Jun 25 at 8:35
  • $\begingroup$ @IvanNeretin Thank you for sharing your knowledge. $\endgroup$ Jun 25 at 8:43
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This is simply a matter of how shapes are defined - and this is by positions of the nuclei only.

Electron pairs are not taken into account, yet of course may explain why a certain shape is preferred.

Say we take a look at a single Ne-atom - one would not call it an octahedron either.

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