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Arrange the following in correct order o...

Arrange the following in correct order of Lewis acidity `BF_(3), BCl_(3), BBr_(3)`.

A

`BF_(3) gt BBr_(3) gt BCl_(3)`

B

`BF_(3) gt BCl_(3) gt BBr_(3)`

C

`BF_(3) lt BCl_(3) lt BBr_(3)`

D

`BBr_(3) lt BF_(3) lt BCl_(3)`

Text Solution

AI Generated Solution

The correct Answer is:
To arrange the compounds BF3, BCl3, and BBr3 in the correct order of Lewis acidity, we need to analyze the factors that influence their acidity. Here’s a step-by-step solution: ### Step 1: Understand Lewis Acids Lewis acids are defined as species that can accept an electron pair. Therefore, the strength of a Lewis acid depends on its ability to accept electrons. **Hint:** Remember that the ability to accept electrons is influenced by the presence of empty orbitals and the stability of the resulting complex. ### Step 2: Analyze BF3 In BF3, boron has an empty p-orbital and can accept electron pairs. However, there is significant back-bonding due to the high electronegativity of fluorine. The lone pair of electrons on fluorine can overlap with the empty p-orbital of boron, which stabilizes BF3 and reduces its tendency to accept additional electron pairs. **Hint:** Consider the effect of back-bonding in BF3 due to the electronegativity of fluorine. ### Step 3: Analyze BCl3 In BCl3, the size difference between boron and chlorine leads to less effective back-bonding compared to BF3. Chlorine has a larger atomic radius than fluorine, which means that the overlap between the orbitals is not as significant. Therefore, BCl3 is more Lewis acidic than BF3 because it can more readily accept electron pairs. **Hint:** Think about how the size of the halogen affects the ability to form back-bonds. ### Step 4: Analyze BBr3 BBr3 has even larger bromine atoms compared to chlorine. This means that there is minimal back-bonding, similar to BCl3. However, because bromine is larger than chlorine, the electron repulsion is less significant, allowing BBr3 to accept electron pairs more easily than BCl3. **Hint:** Compare the atomic sizes of chlorine and bromine and their effect on Lewis acidity. ### Step 5: Arrange in Order of Lewis Acidity Based on the analysis: - BF3 has the least Lewis acidity due to back-bonding. - BCl3 is more acidic than BF3 but less than BBr3. - BBr3 has the highest Lewis acidity because it has the least back-bonding and can accept electrons more readily. Thus, the correct order of Lewis acidity is: **BF3 < BCl3 < BBr3** **Final Answer:** BF3 < BCl3 < BBr3
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