Question
Use the Madelung constant for the NaCl lattice (1.74756) for CaF. and the Madelung constant for the CaF_2 lattice (2.1939) for KF_2 Using these estimates and the data from question I, construct thermodynamic cycles to estimate DeltaH^+, for the formation of CaF and KF_2 from the elements in their standard states (This is in some way, the reverse of what we did for NaCl in class. There, we took the DeltaH^+ and derived an experimental lattice enthalpy; here, we start with a theoretical lattice enthalpy. and figure out what the theoretical DeltaH^+ would be for a hypothetical compound)
Explanation / Answer
3. CaF and KF2 are not observed in nature.
Because in CaF, Ca has +1 charge (group IIA elements exhibit stable +2 charge) and is unstable. In KF2, K has +2 charge (group IA elements exhibit stable +1 charge) which is also unstable. The compounds CaF and KF2 are unstable. Therefore they are not observed in nature, not sold by chemical companies.