Question

Select all the molecules and/or ions for which the molecular shape differs from the parent structure.

A. SiCl₄
B. NH₄⁺
C. H₂Se
D. SF₂

Answer 1

The molecules and/or ions for which the molecular shape differs from the parent structure are A. SiCl₄ and D. SF₂.

Therefore the best answer is option A. SiCl₄ and D. SF₂.

Step-by-step explanation:

In molecular geometry, the shapes of molecules or ions are determined by the arrangement of their atoms and lone pairs around the central atom, following VSEPR (Valence Shell Electron Pair Repulsion) theory. SiCl₄ is tetrahedral, where the central silicon atom is surrounded by four chlorine atoms. However, while the parent structure of SF₂ is linear, its molecular shape differs as it experiences the influence of lone pairs on the sulfur atom, resulting in a bent or angular shape. This deviation occurs because of the presence of two lone pairs on the sulfur atom, which repel the bonding pairs, causing the two fluorine atoms to orient themselves in a bent shape instead of a linear arrangement.

NH₄⁺ and H₂Se do not exhibit a different molecular shape from their parent structures. NH₄⁺, the ammonium ion, retains a tetrahedral shape as it involves four hydrogen atoms surrounding the central nitrogen atom with no lone pairs. Similarly, H₂Se, hydrogen selenide, adopts a linear molecular shape with two hydrogen atoms flanking the central selenium atom, adhering to its parent structure's linearity without any deviation in its molecular shape due to lone pairs or other factors. Therefore, only SiCl₄ and SF₂ demonstrate molecular shapes differing from their respective parent structures due to the influence of lone pairs or variations in bonding arrangements.

Therefore the best answer is option A. SiCl₄ and D. SF₂.

Answer 2

The molecular shapes of NH₄⁺ and SF₂ differ from their respective electron pair geometries due to the presence of lone pairs, causing deviations from the expected shapes predicted by VSEPR theory.

Step-by-step explanation:

The molecular shape of a compound is determined by its electron pair geometry and molecular geometry. In this case, NH₄⁺ (ammonium ion) and SF₂ are the molecules/ions where the molecular shape differs from the parent structure.

NH₄⁺ has a tetrahedral electron pair geometry due to its four bonding pairs of electrons around the central nitrogen atom. However, its molecular geometry is trigonal pyramidal due to the presence of one lone pair on nitrogen, resulting in the deviation from the ideal tetrahedral shape.

SF₂ undergoes a similar change in molecular shape. According to the VSEPR theory, SF₂ has a linear electron pair geometry due to the two bonding pairs of electrons around sulfur. However, the presence of two lone pairs on sulfur causes the molecular geometry to be bent or V-shaped, differing from its linear electron pair geometry.

These differences in molecular shape from the parent structures (electron pair geometry) occur due to the presence of lone pairs, which repel other electron pairs more strongly than bonding pairs. The repulsion between lone pairs and bonding pairs causes distortions in the molecular shape, leading to deviations from the expected geometries predicted by VSEPR theory.

Calculations are not required in this context since the determination of molecular shape primarily relies on the arrangement of bonding and non-bonding electron pairs around the central atom based on VSEPR theory. The observed deviations in NH₄⁺ and SF₂ from their respective electron pair geometries to their molecular shapes can be explained by considering the influence of lone pairs on the overall molecular geometry.