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I understand that bond strength is determined by bond length, and that triple bonds are stronger than double bonds, and double bonds stronger than single; however, I don't understand how you can determine which bond is stronger between two compounds with nearly identical Lewis structures but with different bonding elements from the same group. For example, how do you know whether the CCl4 or CBr4 bonds are stronger?
I might be wrong but I think to answer your question, the stronger bond is the one with the more electronegative atom involved. For instance, the bonds are stronger than those of the molecule because Cl is a more electronegative atom. Electronegative atoms hold electrons more tightly and therefore increase the strength of the bond, just like ionic bonds are stronger than covalent because one of the atoms in an ionic bond is usually very electronegative.
Bond strength is also directly related to atom size. Larger atoms have a larger distance so a longer bond length, and because longer bonds are are weaker, large atoms form weaker bonds. So you can compare bond strength in a group because as you go down a group atom size increases. Therefore CCl4 would have stronger than CBr4.
The stronger bond is in the molecule with the more electronegative atom involved. For instance, the bonds in CCl4 are stronger than those of the CBr4 because Cl has a higher electronegativity than Br due to Cl's smaller size. Electronegative atoms hold electrons more tightly, thus increasing the strength of the bond.
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