Problem 85 - Chemistry The Central Science In Si Units

Question

Consider the collection of nonmetallic elements: \(\mathrm{B}\), As, \(\mathrm{O}\), and I. (a) Which two would form the most polar single bond? (b) Which two would form the longest single bond? (c) Which one would be likely to form a compound of formula \(\mathrm{XY}_{3}\) ? (d) Which element would likely to participate in two covalent bonds?

Step-by-Step Solution

Answer

(a) \((\mathrm{O}, \mathrm{As})\); (b) \((\mathrm{As}, \mathrm{I})\); (c) \(\mathrm{B}\); (d) \(\mathrm{O}\).

Step 1: Introduction to Nonmetallic Elements

We are examining the elements: Boron (\(\mathrm{B}\)), Arsenic (\(\mathrm{As}\)), Oxygen (\(\mathrm{O}\)), and Iodine (\(\mathrm{I}\)). To solve parts (a)-(d), we need to consider electronegativity, atomic size, and typical valency of these elements.

Step 2: Determine Bond Polarity

Electronegativity is key in determining bond polarity. Oxygen (\(\mathrm{O}\)) has the highest electronegativity among these elements, and arsenic (\(\mathrm{As}\)) has one of the lowest. The bond between \(\mathrm{O}\) and \(\mathrm{As}\) would be the most polar single bond, as they have the largest difference in electronegativity.

Step 3: Determine Bond Length

Bond length typically depends on atomic size. Arsenic (\(\mathrm{As}\)) and Iodine (\(\mathrm{I}\)) are the largest atoms in the list. Therefore, the single bond between these two elements would likely be the longest.

Step 4: Determine Compound Formation of the Type \(\mathrm{XY}_3\)

The formation of \(\mathrm{XY}_3\) suggests an element that can form three covalent bonds. Boron (\(\mathrm{B}\)), typically forms \(\mathrm{BX}_3\) type compounds, such as \(\mathrm{BF}_3\). This is because boron commonly forms three bonds, utilizing the 2s and 2p orbitals.

Step 5: Determine Element Likely to Form Two Covalent Bonds

Elements that typically form two covalent bonds include oxygen (\(\mathrm{O}\)), which often forms compounds like water (\(\mathrm{H}_2\mathrm{O}\)). This is because oxygen usually completes its valence shell by sharing two electrons, forming two bonds.

Key Concepts

Electronegativity

Electronegativity measures an atom's ability to attract and hold onto electrons in a covalent bond. Its significance is immense in understanding how atoms interact within molecules. Generally, elements with high electronegativity values tend to pull electrons closer. Oxygen, for instance, has one of the highest electronegativity values among nonmetals, making it incredibly effective at forming polar bonds. In our given task, comparing oxygen and arsenic, the bond would be highly polar due to the significant electronegativity difference between them. Electronegativity values help us predict electron distribution in molecules, influencing the physical properties of a substance, such as melting and boiling points.

Bond Length

Bond length refers to the average distance between the nuclei of two bonded atoms. It is crucial in determining the stability and characteristics of a molecule. Typically, larger atomic radii result in longer bond lengths. For instance, arsenic (As) and iodine (I) are relatively large compared to oxygen (O) and boron (B). When these two large atoms form a bond, the distance between their nuclei is greater, resulting in a longer bond length. Longer bonds are generally weaker, affecting the molecule's reactivity and flexibility. Understanding bond length is essential for predicting molecule behavior in chemical reactions and interactions.

Valency

Valency is an atom's ability to bond with other atoms, primarily determined by the number of valence electrons available for bonding. It is a fundamental concept in predicting chemical compound formation. Boron (B) is a classic example, as it frequently forms compounds like \(\mathrm{BX}_3\) where it forms three covalent bonds. Boron has three valence electrons, which it commonly uses in forming three single bonds to achieve a stable configuration. Recognizing an element's valency allows us to determine possible molecular structures and formulas, providing insights into chemical reactivity and stability.

Nonmetallic Elements

Nonmetallic elements, such as boron (\(\mathrm{B}\)), arsenic (\(\mathrm{As}\)), oxygen (\(\mathrm{O}\)), and iodine (\(\mathrm{I}\)), have unique properties that distinguish them from metals. They are generally poor conductors of electricity and have high electronegativities, which makes them effective in forming covalent bonds. Due to their varied valence electron configurations, nonmetallic elements can form a wide variety of compounds with differing properties. Understanding the characteristics of nonmetals is essential in chemistry, helping us predict how they will interact and bond with each other. For instance, nonmetals readily form compounds with each other through the sharing of electrons, highlighting the versatile nature of their chemical bonding capabilities.