Problem 13 - A Complete Resource Book in Chemistry for JEE Main

Question

Mark the wrong statement which of the following statements about/regarding \(\mathrm{BF}_{3}\) is incorrect? (a) it forms an addition compound with \(\mathrm{NH}_{3}\) (b) it is a volatile liquid at room temperature (c) it combines with either to form boron trifluoride etherate (d) it acts as a Lewis acid

Step-by-Step Solution

Answer

Statement (b) is incorrect. \(\mathrm{BF}_3\) is a gas at room temperature.

Step 1: Understanding the properties of BF_3

Boron trifluoride (\(\mathrm{BF}_3\)) is a chemical compound known for its Lewis acid properties, meaning it can accept an electron pair. It's commonly used in addition reactions due to its electron deficiency.

Step 2: Analyzing the formation of addition compounds

\(\mathrm{BF}_3\) forms an addition compound with \(\mathrm{NH}_3\) because nitrogen in ammonia donates a lone pair to boron, which lacks an octet. This forms a stable adduct. Therefore, statement (a) is correct.

Step 3: Examining the physical state of BF_3

\(\mathrm{BF}_3\) is actually a gas at room temperature, not a liquid. Thus, statement (b) describes it incorrectly, making it a potential wrong statement.

Step 4: Combining with ether to form a complex

\(\mathrm{BF}_3\) reacts with ether to form boron trifluoride etherate. The oxygen in ether donates a lone pair of electrons to form this complex, so statement (c) is correct.

Step 5: Confirming Lewis acid behavior

As a compound short of electrons, \(\mathrm{BF}_3\) can accept electron pairs, thus behaving as a Lewis acid. Therefore, statement (d) is accurate.

Key Concepts

Lewis Acid

A Lewis acid is a chemical species that can accept an electron pair. This concept is essential in understanding how reactions and bonding occur in various compounds. Boron trifluoride ( BF_3 ) exemplifies a Lewis acid because it has an empty orbital and a deficiency of electrons. The boron atom in BF_3 has only six electrons in its valence shell, two less than the stable octet norm.
This deficiency allows it to readily accept electron pairs from other molecules, such as ammonia ( NH_3 ), which donates a lone pair for bonding. This behavior marks BF_3 as a classic Lewis acid. Being a Lewis acid is significant as it sees widespread application in catalyzing reactions, facilitating the formation of stable complexes by electron pair acceptance.

Addition Compounds

Addition compounds form when two molecules join by sharing an electron pair. Boron trifluoride's electron deficiency enables the formation of these compounds. When BF_3 encounters a molecule like ammonia (NH_3), a stable addition compound known as an adduct forms.
The nitrogen atom in ammonia has a lone pair of electrons, which it can donate to the electron-deficient boron in BF_3. This donation allows the two compounds to form a coordinate covalent bond, where both electrons come from the nitrogen.
Addition compounds like this illustrate the interactive dynamics between electron-rich and electron-poor species, a foundational concept in understanding chemical reactivity and compound stability.

Physical States of Compounds

The physical state of a compound at room temperature can affect how it is used and stored. Boron trifluoride, for instance, typically exists as a gas under standard conditions. This is an important distinction, as some may mistakenly believe it is a volatile liquid.
Knowledge of the correct physical state of BF_3 is crucial for its handling and application. As a gas, it requires specific storage and transport conditions to ensure safety and effectiveness in industrial and laboratory settings. Understanding the physical state helps predict its behavior in various environments and informs how it can best be utilized in chemical processes.

Electron Pair Acceptance

Electron pair acceptance is at the heart of many chemical interactions, especially involving Lewis acids. Boron trifluoride's ability to accept electron pairs demonstrates this principle vividly.
In an electron pair acceptance process, the iodine of electrons is often provided by a donor molecule that possesses lone pairs. In BF_3's case, the boron atom's electron deficiency results in its proclivity for accepting these pairs.
This process can be seen when BF_3 forms addition compounds with molecules like ether and ammonia. When you understand electron pair acceptance, you gain insight into how molecules interact and bond, shedding light on reaction mechanisms and energetics that guide compound formation and stability.