What Is The Molecular Geometry Of SeH2?

H2Se adopts a “curved” structure with an H-Se-H bond angle of 91°.

You can make useful comparisons with HOH [H2O] and H-SH [H2S]. To explain this, it would be important for you to understand hybridization theory. The bond angle of HOH is 105 and that of H-SH is 92. This suggests that S is barely hybridized and, in fact, uses p orbitals (with few s features) to form SH bonds, while O is sp3 hybrid.

To understand why S is not hybridized, we need to understand that the large size of S allows electron pairs to be far apart, so the resulting repulsive energy is not very large and n does not need to be minimized. As the O is much smaller, a more stable and less energetic configuration would have to be made – hence the hybridization.

Each of the molecules H2O, H2Se, H2Te has two unbonded pairs of electrons. They come from the atoms O, Se, Te which are found in successive rows of the periodic table. As a result, the pairs of electrons are less and less attracted towards the nuclei. Due to this weaker attraction, lone pairs take up more space. This, in turn, causes the bond angle of the Hs to become more acute. This reasoning is just one example of a semi-empirical binding model called: Valence Shell Electron Pair Repulsion (VSEPR).

Source(s): retired chemical examiner

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The basic geometry is determined by the number of electron pairs whether they are bonded or not. SeH2 is surrounded by four pairs of electrons, two of which bond and two are lone pairs. The geometry of the electron pair is tetrahedral. The molecular geometry is curved and the bond angle is just under 109.5 degrees. It turns out that the bond angle is much less than 109.5 degrees, closer to 95 degrees, due to the large size of Se and the scattering of delocalized lone pairs that bring the bond pairs closer together.