Question

Which of the following has the weakest bond?
A. \[{H_2}\]
B. \[L{i_2}\]
C. \[{F_2}\]
D. \[{O_2}\]

Answer 1

Hint: In a periodic table, as we move from left to right in a period, the size of the elements decreases. Because as we move from left to right the shell remains the same and the electron is adding up to the same shell.

Complete Step by step answer:
When the two atoms bond together to form a molecule, their electrons bond them together by mixing into openings in each other’s orbital. The formation of bonds by the molecule starts at the nearest available orbital shell opening that means mixing of that orbitals occurs at the outermost.

Bond order defines the number of chemical bonds between a pair of atoms and it basically indicates the stability or strength of the molecule. For example in diatomic molecule nitrogen, the bond order is three.
Bond length is defined as the distance between the centers of the two covalently bonded atoms. The length of the bond is determined by the number of bonded electrons that is the bond order in actual terms. The higher the bond order, the stronger will be the bond strength and shorter will be the length then. So the bond lengths of single bonds will be more than that of double bond and triple bond.
Generally the bond length between the two atoms is approximately the sum of the covalent radii of the two atoms.

The bond length and bond order indicates the type and strength of covalent bonds between the atoms.
Here in the question we have asked the weakest bond. Since the bond between \[{H_2},L{i_2},{F_2},\] is single bond order is 1 and bond between \[{O_2}\] is double that means bond order is 2. And we know molecules with 2 bond order will be stable. Now for remaining molecules \[{H_2},L{i_2},{F_2}\]. The size of the lithium element is largest among the fluorine and hydrogen. As hydrogen has only one orbital. And fluorine and lithium have 2 orbitals. And as we move from left to right in a period, the size of the elements decreases. So \[L{i_2}\] will have the highest bond length and hence the bond will be weakest.

Hence the correct option will be B.

Note: If bond order is zero for any molecule, that means that molecule cannot be formed. The higher bond orders indicate greater stability. In the molecule that has resonance between the double and triple bonds, the bond order does not need to be an integer.