= Solution
\b[Group 6:] cohesion increases from <chromium> to <molybdenum> to <tungsten>. partially occupied d bands make a major contribution to metallic cohesion. Relative to localized 3d orbitals in Cr, more extended 4d/5d orbitals support stronger overlap and broader bonding bands. Strong 5d bonding and the compact dimensions associated with lanthanide/relativistic effects help make W especially cohesive.
\b[Group 11:] cohesion increases from <silver> to <copper> to <gold>. the filled d shell changes the balance from Group 6. Going from Cu to larger Ag weakens overlap and lowers cohesion. <Gold> reverses that simple size trend: relativistic 6s stabilization/contraction, changes in the 5d orbitals and stronger s-d participation enhance bonding. A size-only argument cannot explain Au exceeding both Ag and Cu.
\b[Group 15, As > Sb > Bi:] bonding in these elemental solids involves directional p-orbital interactions. Increasing size and longer separations weaken overlap down the group, reducing <enthalpy of atomization>. Changes in detailed solid structure and relativistic effects refine the numbers, but the underlying weakening of p-derived bonding explains the trend.
<Enthalpy of atomization> measures removal from the entire standard-state solid to gaseous ground-state atoms; it is not simply the dissociation energy of one selected diatomic bond.
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