Bond Energies

[MedPR]

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2 questions given the following BDE:

1. Why would a Br-F bond be stronger than a Br-Cl bond?
2. Why would a Br-Cl bond be weaker than a Cl-F bond?

F-F 154
Cl-Cl 239
Br-Br 193
I-I 149
Cl-F 253
Br-Cl 218
I-Cl 208
I-Br 175

 

[pfaction]

Electronegativity? F is stronger electronegatvitiy than Chlorine. BR-C is almost ionic, whereas Fluorine AND Bromine want to hang on to the electrons?

 

[MedPR]

Electronegativity? F is stronger electronegatvitiy than Chlorine. BR-C is almost ionic, whereas Fluorine AND Bromine want to hang on to the electrons?

Sorry, the OP was supposed to say Br-Cl, not Br-C.

 

[pfaction]

Alright no biggie.
Br-F: Br isn't as electronegative as F, so F hogs it. It's small, it wants it real bad.
Br-Cl: Cl is certainly more electronegative but also bigger. So it's strong, but not as much as F.

Br-Cl: Good bonding, biggish atoms. Cl wants it.
Cl-F: Two electronegative atoms! They're gonna hold onto those electrons for sure and not let go.

So IMO:
Br-Cl < Br-F < Cl-F <F-F in strength. Note I did not read the numbers. I'm going to check if I am right.

 

[pfaction]

Just a small update.

TBR, Gen Chem p98 above Ex 2.17:
TThe smaller the atomic radius of the atom, the shorter the bond it forms when sharing electrons with another atom. Shorter bonds are stronger bonds, so there exists a correlation between an elements location in the periodic table and the strength of the bonds that the element can form.

 

[MedPR]

Thanks. Not sure what I was thinking when I was doing this passage. Obviously two electronegative atoms form a stronger bond than a less electronegative.

 

[wild2taz]

I just did this question in tbr chem p169 narrowed it down to 2 choices, picked the wrong one cause I didn't realize F-Cl bond energy was given in table, careless :/