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Question: How many of the following order of bond energies are correct. A. \(C - C\, > \,Si - Si\) B. \(C ...

How many of the following order of bond energies are correct.
A. C−C > Si−SiC - C\, > \,Si - Si
B. C−O > Si−OC - O\, > \,Si - O
C. C−F > Si−FC - F\, > \,Si - F
D. C−F < Si−FC - F\, < \,Si - F
E. C−H > Si−HC - H\, > \,Si - H
F. Si−Cl > C−ClSi - Cl\, > \,C - Cl
G. Si−Si > C−SiSi - Si\, > \,C - Si
H. C−Br>Si−BrC - Br > Si - Br

Explanation

Solution

The above question deals with the basic concepts of periodic properties. Here if you know about the periodic trend of bond length, electronegativity etc. you can easily solve the question. Now remember that most of the bonds formed above are between silicon and carbon both lie in the same group but silicon is bigger in size than carbon.

Complete step-by-step answer: Let’s discuss the first option that is bond between two carbon atoms and two silicon atoms, we know that on moving down the group size of an atom increases thus bond energy will decrease, so our first option is correct as silicon is next to carbon the bond that it forms will have lesser strength or energy than carbon-carbon bond. Option A is correct.
Next we have a bond of oxygen with carbon and silicon where you will see the concept of electronegativity. As oxygen is an electronegative atom and if it will form a bond with carbon and silicon, more polar bonds will be formed with silicon due to electronegativity difference. Bond energies for C−OC - O was found to 358 kJ mol−1358\,kJ\,mo{l^{ - 1}} and for Si−OSi - O it is 452 kJ mol−1452\,kJ\,mo{l^{ - 1}} . This option B is incorrect.
For the bond between carbon and fluorine and silicon and fluorine, it was found that the bond formed between silicon and fluorine is stronger than carbon and fluorine. This is also due to the electronegativity difference. Thus option C is incorrect while option (D) is correct.
Option (E) is correct because electronegativity of carbon is more than that of silicon. Another reason can be the size, as we move down the group the size increases and thus we will get a weaker bond. Next we have a bond between carbon and chlorine, silicon and chlorine here bond between carbon and chlorine C−ClC - Cl is weaker than the Si−ClSi - Cl this is due to the higher degree of ionic character in case of silicon. Option (F) is correct. In option (G), bond strength of Si−CSi - C bond was found to be 318 kJ mol−1318\,kJ\,mo{l^{ - 1}} which very high value than the bond strength is of Si−SiSi - Si which is 222 kJ mol−1222\,kJ\,mo{l^{ - 1}} . Option (G) is wrong. Similarly, if we talk about the bond strength of carbon to bromine bond it will be having value 275 kJ mol−1275\,kJ\,mo{l^{ - 1}} while when silicon form bond with bromine it will be having bond strength of about 310 kJ mol−1310\,kJ\,mo{l^{ - 1}} this can be understood on the basis of ionic strength which is more in Si−BrSi - Br than in C−BrC - Br. Hence, option (H) is incorrect.

Correct options are: A, D, E and F.

Note: Don’t get confused only with the reason of electronegativity or size changes on moving down the group in periodic table. There may see changes in bond strength due to ionic character, shielding effect etc. But many questions can be solved if basic concepts of periodic properties are clear. Here many bond strengths are higher for silicon than carbon bonds, the reason is the ionic character.