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Magazine Chapter 16: Problem 137
In which of the following pairs, the two species are iso-structural? (a) \(\mathrm{SF}_{4}\) and \(\mathrm{XeF}_{4}\) (b) \(\mathrm{SO}_{3}^{2}\) and \(\mathrm{NO}_{3}^{-}\) (c) \(\mathrm{BF}_{3}\) and \(\mathrm{NF}\) (d) \(\mathrm{BrO}_{3}^{-}\)and \(\mathrm{XeO}_{2}\)
Short Answer
Expert verified
None of the pairs are iso-structural.
Step by step solution
01
Define Iso-structural Species
Iso-structural species are molecules or ions that have the same shape and the same type of hybridization at the central atom. This means they have identical geometrical structures and similar electron pair arrangements around the central atoms.
02
Analyze Option (a): SF鈧� and XeF鈧�
SF鈧� has a seesaw shape due to its trigonal bipyramidal electron pair geometry (one lone pair), while XeF鈧� has a square planar shape with two lone pairs on xenon. These shapes are not the same, so they are not iso-structural.
03
Analyze Option (b): SO鈧兟测伝 and NO鈧冣伝
SO鈧兟测伝 (sulfite ion) has a trigonal pyramidal shape due to the presence of a lone pair on sulfur. NO鈧冣伝 (nitrate ion) is planar with no lone pairs on nitrogen. Since their shapes differ, they are not iso-structural.
04
Analyze Option (c): BF鈧� and NF
BF鈧� is a planar trigonal shape because the boron is surrounded by three fluorine atoms and has no lone pairs, but NF is not a common simple molecule; likely it refers to NF鈧�. NF鈧� has pyramidal geometry due to lone pair presence, making the shapes different from BF鈧�. Thus, BF鈧� and NF and incorrectly implied NF鈧� are not iso-structural.
05
Analyze Option (d): BrO鈧冣伝 and XeO鈧�
BrO鈧冣伝 is a trigonal pyramidal ion due to the presence of a lone pair on bromine, while XeO鈧� is typically a linear molecule. Their structures are different as well, thus they are not iso-structural.
06
Conclusion from Analysis
From the analysis of all options, each pair has differing molecular geometries and therefore no pair consists of iso-structural species. Contrary to the listed options, none of these pairs demonstrates iso-structurality.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Molecular Geometry
In chemistry, molecular geometry refers to the three-dimensional arrangement of atoms within a molecule. Understanding molecular geometry is crucial as it influences physical and chemical properties such as polarity, reactivity, phase of matter, color, magnetism, biological activity, and much more. Essentially, the shape of a molecule is determined by the regions of electron density around the central atom such as bonds and lone pairs. Here are some common molecular geometries:
- Linear: A straight-line arrangement, e.g., CO2.
- Trigonal Planar: Three atoms arranged at the corners of an equilateral triangle around the central atom, e.g., BF3.
- Tetrahedral: Four atoms forming a structure similar to a tripod, e.g., CH4.
- Trigonal Bipyramidal: Five atoms where three lie in a plane and two above and below the plane, e.g., PCl5.
- Square Planar: Four surrounding atoms form a square around the central atom, e.g., XeF4.
Hybridization
Hybridization is a concept in which atomic orbitals mix to form new hybrid orbitals. These hybrid orbitals have different energies and shapes compared to the original atomic orbitals, which results in molecules having specific geometries.
Different types of hybridization account for different shapes:
Different types of hybridization account for different shapes:
- sp Hybridization: Linear shape with a bond angle of 180掳.
- sp2 Hybridization: Trigonal planar shape with bond angles of 120掳.
- sp3 Hybridization: Tetrahedral shape with bond angles of 109.5掳.
- sp3d Hybridization: Trigonal bipyramidal shape, e.g., SF4, due to lone pair, becomes seesaw.
- sp3d2 Hybridization: Octahedral shape or square planar shape, e.g., XeF4.
Electron Pair Geometry
Electron pair geometry refers to the spatial arrangement of all pairs of electrons around a central atom, including both bonding pairs and lone pairs. This concept is determined by the number of electron groups around a central atom, where each group might be a single bond, multiple bond, or lone pair.
VSEPR theory (Valence Shell Electron Pair Repulsion) helps predict the electron pair geometries by assuming that electron pairs will arrange themselves to be as far apart as possible to minimize repulsion:
VSEPR theory (Valence Shell Electron Pair Repulsion) helps predict the electron pair geometries by assuming that electron pairs will arrange themselves to be as far apart as possible to minimize repulsion:
- Two electron groups: Linear geometry.
- Three electron groups: Trigonal planar geometry.
- Four electron groups: Tetrahedral geometry.
- Five electron groups: Trigonal bipyramidal geometry.
- Six electron groups: Octahedral geometry.
Lone Pairs
Lone pairs refer to pairs of valence electrons that are not involved in chemical bonding within a molecule. These non-bonding pairs significantly influence the shape and properties of molecules.
- Presence and Impact: While lone pairs do not participate in forming bonds, they exert repulsive forces on adjacent electron pairs. This repulsion can lead to bond angles being smaller than expected, making the molecular shape different from the electron pair geometry.
- Influencing Geometry: For instance, a tetrahedral electron pair geometry with one lone pair results in a trigonal pyramidal molecular shape, like in NH3.
- Effect on Polarity: Lone pairs can also contribute to molecular polarity, affecting how a molecule interacts with other substances and their solubility, boiling/melting points, and more.
