Question

Boron and silicon resembles in all respects except (a) Both form halides which are Lewis acids (b) Their chlorides hydrolyse to their respectively acids (c) Both form acidic oxides (d) Their hydrates are stable

Short answer

Option (b) is the exception.

Step-by-step solution

Understanding the Question

The question asks us to determine the property in which boron and silicon do not resemble each other. We need to analyze each given option to identify which one is the exception.

Analyzing Option (a)

Option (a) states that both boron and silicon form halides which are Lewis acids. Boron halides like BF extsubscript{3} and silicon halides like SiF extsubscript{4} act as Lewis acids by accepting electron pairs. This option indicates a similarity.

Analyzing Option (b)

Option (b) mentions that their chlorides hydrolyze to form their respective acids. Boron chloride (BCl extsubscript{3}) hydrolyzes to form boric acid (H extsubscript{3}BO extsubscript{3}), while silicon tetrachloride (SiCl extsubscript{4}) hydrolyzes to form silica (SiO extsubscript{2}) and hydrochloric acid (HCl), not separately a silicon acid. Hence, hydrolysis results are not analogous, making this option a potential exception.

Analyzing Option (c)

Option (c) claims that both boron and silicon form acidic oxides. Boron forms B extsubscript{2}O extsubscript{3}, and silicon forms SiO extsubscript{2}, both of which are acidic in nature. Therefore, this option is a similarity.

Analyzing Option (d)

Option (d) says their hydrates are stable. Boron does form some stable compounds with hydrates, such as boronic acids, but silicon hydrates like orthosilicic acid are generally less stable in aqueous solutions. This could be considered an exception, but less probable than option (b).

Conclusion

Comparing all options, option (b) is the most distinct difference as the results of hydrolysis lead to different categories of compounds (an acid for boron and non-acidic oxides for silicon). Therefore, option (b) is likely the one where boron and silicon do not resemble each other except.

Key concepts

Lewis Acids

In chemistry, Lewis acids are compounds that can accept an electron pair. This makes them eager to bond with compounds that can donate electron pairs, usually called Lewis bases. A classic example in this category involves halides of elements such as boron and silicon. For instance, boron trifluoride (BF\(_3\)) and silicon tetrafluoride (SiF\(_4\)) act as Lewis acids.

A Lewis acid often contains an atom that has an incomplete outer electron shell. It naturally seeks out electron pairs from other molecules to achieve stability. Because of this, these acids play a significant role in many chemical reactions, especially in forming covalent bonds.

• Boron halides are superb Lewis acids because the boron atom readily accepts electron pairs due to having an electron-deficient structure.
• Silicon halides, while generally less reactive than boron halides, still exhibit Lewis acid behavior, particularly in renowned applications such as creating glass coatings and resins.

Understanding Lewis acids gives us insight into why certain reactions occur and helps in the development of materials and chemicals with specific desired properties.

Hydrolysis of Chlorides

Hydrolysis is the chemical breakdown of a compound due to the reaction with water. Some chlorides undergo this process and transform into different chemical entities in water.

For instance, boron trichloride (BCl\(_3\)) reacts with water quite interestingly. It undergoes hydrolysis to form boric acid (H\(_3\)BO\(_3\))—an acid well-known for its mild antiseptic properties.

Silicon tetrachloride (SiCl\(_4\)), however, behaves differently. Upon hydrolysis, it results in the formation of silicon dioxide (SiO\(_2\)) and hydrochloric acid (HCl). Silicon dioxide is an oxide rather than an acid, marking a distinct contrast in this regard compared to boron chlorides.

• Hydrolysis of boron chloride produces an actual acid, uniquely significant in medicinal and antiseptic use cases.
• This distinct outcome from silicon tetrachloride hydrolysis illustrates why certain chemical processes are unique between elements, such as producing oxides instead of acids.

Understanding hydrolysis outcomes sharpens our comprehension of element behavior and is pivotal for applications ranging from manufacturing to pharmaceuticals.

Acidic Oxides

Acidic oxides are compounds that react with water to form acids, or with bases to form salts. They are typically oxides of non-metals. Both boron and silicon form acidic oxides, showcasing similarities in this category.

Boron forms boron trioxide (B\(_2\)O\(_3\)), which is acidic and forms boric acid when dissolved in water. It's often utilized in glass and ceramics manufacturing due to its properties.

Silicon produces silicon dioxide (SiO\(_2\)), an essential oxide in many industries. While it is acidic, in practical contexts, it mainly forms silicic acid under certain conditions, rather than serving as a direct source of acid in chemistry experiments.

• Acidic oxides like B\(_2\)O\(_3\) interact with water to produce acids, highlighting their role in numerous chemical environments.
• SiO\(_2\) is a prime component of sand and used extensively in technology, primarily in microelectronics and construction.

Understanding the formation and usage of acidic oxides is key in industrial applications. Their versatile nature sees them implemented in everything from electronics to environmental management systems.