a. Predict the relative lengths and strengths of the bonds

Solution:

Here we have to predict the relative length and strength of the given bonds.

How to predict the relative length and strength:-

The relative length of an atom depends on the number of shells present in it. Greater the number of shells present in an atom, the distance between the nucleus and valence shell electron will also increase.Thus electrons in atomic orbitals farther from the nucleus form longer bonds.  

The bond strength is inversely proportional to the bond length, i.e a molecule having higher bond length will have weaker bond strength due to less electron density in the region of orbital overlap.

Bond strength

Step 1

(a)

Cl and Br both are present in the same group (group-16 halogens) in the periodic table. It is known that as we move down a group the atomic size increases, greater the atomic size longer will be the bond length.

Hence the bond length of the Br-Br bond is higher than that of Cl-Cl bond.

As bond strength is inversely proportional to bond length, thus Br2 has weaker strength than Cl2.

Therefore the relative bond length:-  Br2 > Cl2

Relative bond strength:- Cl2 > Br2