Which statement about atomisation energy is true?

• A. It is exothermic because bonds are formed
• B. It is exothermic because energy is released when atoms form
• C. It is endothermic because energy is required to convert a solid element into gaseous atoms
• D. It is independent of bond strength

Answer: (C)

Atomisation energy is the energy required to turn a substance into gaseous atoms, i.e., to break all the bonds that hold the atoms together in the solid or molecule. For a solid element, this means overcoming the lattice or cohesive forces to produce isolated gaseous atoms, which requires input of energy. That makes the process endothermic, so the atomisation enthalpy is positive. The idea that it’s exothermic because bonds are formed doesn’t apply here, since atomisation involves breaking bonds, not forming them. Also, the magnitude depends on how strongly the atoms are held together: stronger bonding or a tighter lattice means more energy is needed, so atomisation energy is not independent of bond strength.