Question

Which molecule has a tetrahedral arrangement of electron pairs but is not a tetrahedral molecule?

methane

water

carbon dioxide

boron trifluoride

Answer 1

Water

Step-by-step explanation:

Electron geometry (arrangement) is tetrahdral but its molecular geometry is bent.

Oxygen has 6 electrons in the outermost shell but it only uses 2 electrons for forming bonds with 2 Hydrogen atoms. The oxygen atom - center atom is surrounded by four electron pairs (2 pairs with 2 Hydrogen atoms, 2 lone pairs) so that its shape is tetrahedral. In contrast, it's supposed to be linear shaped but in fact it has bent molecular geometry due to lone pairs repel other electron pairs more strongly than bonded electrons.

Answer 2

Water

This is due to the fact that the oxygen atom in water also contains two lone pairs of electrons.