What shape would SeH2 have? Draw the molecule
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The Correct Answer and Explanation is:
The shape of the SeH₂ molecule is bent
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H - Se - H
..The shape of a molecule is determined by the Valence Shell Electron Pair Repulsion (VSEPR) theory. This theory states that electron pairs in the valence shell of a central atom will arrange themselves as far apart as possible to minimize repulsion, which in turn determines the molecule’s geometry.
To determine the shape of hydrogen selenide (SeH₂), we first identify the central atom, which is selenium (Se) as hydrogen can only form one bond. Next, we count the total number of valence electrons. Selenium is in Group 16 of the periodic table, so it has 6 valence electrons. Each hydrogen atom is in Group 1 and has 1 valence electron. The total count is 6 + (2 x 1) = 8 valence electrons.
These electrons are arranged around the central selenium atom. Two single covalent bonds are formed between selenium and the two hydrogen atoms, using 4 of the 8 valence electrons. The remaining 4 electrons are placed on the central selenium atom as two non-bonding lone pairs.
This gives the central selenium atom a total of four electron domains: two bonding pairs (the Se-H bonds) and two lone pairs. The arrangement of four electron domains that minimizes repulsion is a tetrahedral electron geometry, with an ideal angle of 109.5 degrees.
However, the molecular shape describes the arrangement of only the atoms, not the lone pairs. When we consider the positions of the atoms within this tetrahedral electron arrangement, we see the selenium atom at the center and the two hydrogen atoms at two of the corners. The two lone pairs occupy the other two corners. Because lone pairs exert a stronger repulsive force than bonding pairs, they push the Se-H bonds closer together, compressing the H-Se-H bond angle to be significantly less than 109.5 degrees. This results in a V-shape, which is correctly described as a bent or angular molecular geometry.
