hii saikat

For covalent molecules bond energy generally depend upon electronegativity and bond length which states that bond energy is directly proportional to electronegativity and inversely proportional to bond length so according to it as we go down the group size increases so as distance between the atom increases which will ultimately decreases bond energy so in this case c-c>si-si>ge-ge>sn-sn has greater bond energy because as two bonded atoms become larger ,the region between them occupied by bonding electrons become smaller so their bonding energy decreases.general trend for bond energy between like atoms are decreases down the group except few atoms.i hope this information helps you.

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