br gchem 2, thermodynamics passage 2 #13

[Rosalindbungs]

Q: What is the approximate bond energy of a Br-F bond?
a. 261 kj/mol
b. 242 "
c. 206 "
d. 161 "

Answer: B; what was given was a Cl-F b.e. of 253 kj/mol.

Why is a Br-F bond weaker than a Cl-F bond?

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[loveoforganic]

Poorer orbital overlap due to the size of bromine

 

[Rosalindbungs]

sorry, can you clarify that? i still don't really understand...

 

[Pamplemousse123]

Br is bigger atom than Cl - how do we know this? from the periodic trends of atomic radius! As we go down a column on a periodic table, there is an additional energy level added. So if we have a bigger atom we have a weaker bond. How? Because bond energy is based upon the bond length. A longer bond is a weaker bond and has less bond energy because the bond is easier to break. The bond length is a measure of the the length of the Br atomic radius + the other element's atomic radius, which in this case is F and because Br is bigger (bigger atomic radius) than Cl, Br-F is weaker than Cl-F. I hope this clarifies your question.