Chapter 4: Problem 82
Which of the following pairs arc nonlincar? (1) \(\mathrm{NH}_{3}, \mathrm{CO}_{2}\) (2) \(\mathrm{NH}_{3}, \mathrm{H}_{2} \mathrm{O}\) (3) \(\mathrm{CO}_{2}, \mathrm{BeCl}_{2}\) (4) \(\mathrm{BeCl}_{2}, \mathrm{NH}_{3}\)
Short Answer
Expert verified
Pair (2): \(\text{NH}_3\), \(\text{H}_2\text{O}\)
Step by step solution
01
Determine the molecular geometry of each molecule
Identify the shape of each molecule using VSEPR (Valence Shell Electron Pair Repulsion) theory. This helps determine if the molecule is linear or non-linear.
02
Molecular geometry of \(\text{NH}_3\)
The ammonia (\(\text{NH}_3\)) molecule has a trigonal pyramidal structure due to the presence of a lone pair on the nitrogen atom. This makes \(\text{NH}_3\) non-linear.
03
Molecular geometry of \(\text{CO}_2\)
The carbon dioxide (\(\text{CO}_2\)) molecule has a linear structure because the central carbon atom forms double bonds with each oxygen atom, aligning directly opposite. This makes \(\text{CO}_2\) linear.
04
Molecular geometry of \(\text{H}_2\text{O}\)
The water (\(\text{H}_2\text{O}\)) molecule has a bent or V-shaped structure due to the two lone pairs on the oxygen atom. This makes \(\text{H}_2\text{O}\) non-linear.
05
Molecular geometry of \(\text{BeCl}_2\)
The beryllium chloride (\(\text{BeCl}_2\)) molecule has a linear structure with beryllium in the center forming single bonds with two chlorine atoms, positioned 180 degrees apart. This makes \(\text{BeCl}_2\) linear.
06
Identify pair (1)
\(\text{NH}_3\) (non-linear) and \(\text{CO}_2\) (linear) are not both non-linear.
07
Identify pair (2)
\(\text{NH}_3\) (non-linear) and \(\text{H}_2\text{O}\) (non-linear) are both non-linear.
08
Identify pair (3)
\(\text{CO}_2\) (linear) and \(\text{BeCl}_2\) (linear) are both linear.
09
Identify pair (4)
\(\text{BeCl}_2\) (linear) and \(\text{NH}_3\) (non-linear) are not both non-linear.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
VSEPR theory
Understanding the shape of a molecule is crucial for predicting its properties and behavior. VSEPR theory, which stands for Valence Shell Electron Pair Repulsion theory, is a fundamental tool in this area. The core idea is that electron pairs around a central atom will repel each other and arrange themselves as far apart as possible. This repulsion shapes the geometry of the molecule. For example, if a molecule has four electron pairs, these pairs will adopt a tetrahedral arrangement to minimize repulsion. This theory helps us understand why molecules like \(\mathrm{NH}_3\), \(\mathrm{H}_2\mathrm{O}\), \(\mathrm{CO}_2\), and \(\mathrm{BeCl}_2\) have their respective shapes. By knowing the number of bonding pairs and lone pairs on the central atom, we can predict whether the molecule will be linear, bent, or have another shape.
Non-linear molecules
Non-linear molecules have shapes that are not straight lines. These shapes arise due to the presence of lone electron pairs or variations in bond angles. A classic example is \(\mathrm{NH}_3\) — ammonia. \(\mathrm{NH}_3\) has three hydrogen atoms bonded to a nitrogen atom and a lone pair on nitrogen. This lone pair pushes down the hydrogen atoms, resulting in a trigonal pyramidal shape.
Another example is \(\mathrm{H}_2\mathrm{O}\) — water. \(\mathrm{H}_2\mathrm{O}\) has two hydrogen atoms bonded to oxygen, which also has two lone pairs. These lone pairs create a bent or V-shape in the \(\mathrm{H}_2\mathrm{O}\) molecule. Non-linear molecules often exhibit unique properties compared to their linear counterparts, such as different polarity and reactivity.
Another example is \(\mathrm{H}_2\mathrm{O}\) — water. \(\mathrm{H}_2\mathrm{O}\) has two hydrogen atoms bonded to oxygen, which also has two lone pairs. These lone pairs create a bent or V-shape in the \(\mathrm{H}_2\mathrm{O}\) molecule. Non-linear molecules often exhibit unique properties compared to their linear counterparts, such as different polarity and reactivity.
Linear molecules
Linear molecules are characterized by atoms positioned in a straight line. This typically occurs when there are no lone pairs on the central atom to repel bonding pairs of electrons, or when the lone pairs are symmetrically arranged. For example, \(\mathrm{CO}_2\) — carbon dioxide — features a central carbon atom double-bonded to two oxygen atoms. These bonds are aligned 180 degrees apart, creating a linear structure.
Similarly, \(\mathrm{BeCl}_2\) — beryllium chloride — is linear because beryllium forms single bonds with two chlorine atoms, which are also positioned 180 degrees apart. Linear molecules often possess specific attributes like non-polarity when the surrounding atoms are identical. These shapes help predict how molecules interact with each other and with various substances.
Similarly, \(\mathrm{BeCl}_2\) — beryllium chloride — is linear because beryllium forms single bonds with two chlorine atoms, which are also positioned 180 degrees apart. Linear molecules often possess specific attributes like non-polarity when the surrounding atoms are identical. These shapes help predict how molecules interact with each other and with various substances.
