Q.Arrange the following alkyl halides in increasing order of bond enthalpy of R-X: CH₃Br, CH₃F, CH₃Cl, CH₃I

The C-X bond in a haloalkane is polar because every halogen is more electronegative than carbon: carbon carries a partial positive charge (delta+), the halogen a partial negative charge (delta-), and the bond itself forms from overlap of carbon's sp3 orbital with the halogen's half-filled p-orbital. Two trends, both driven by halogen ATOMIC SIZE increasing down the group (F -> Cl -> Br -> I), govern every 'arrange in order' question on this topic: bond length increases steadily from C-F (139 pm) to C-I (214 pm) as the bigger halogen sits farther from carbon, and bond enthalpy (strength) decreases correspondingly, from 452 kJ/mol (C-F) down to 234 kJ/mol (C-I) -- a longer bond overlaps its orbitals less effectively and so is weaker. Bond POLARITY (measured by dipole moment) does NOT follow the same simple trend: it actually peaks at C-Cl (1.860 D), not C-F, because dipole moment depends on both the electronegativity difference AND the bond length together (moment = charge x distance) -- fluorine has the biggest electronegativity gap with carbon but also the …