Past exam of the chemistry course of the year 3 of the natural sciences course of the University of Cambridge / 2022 / Paper 4 / 57 / e

Without significant anomalous scattering, the electron density is effectively real and Friedel's law gives $F_0(-\mathbf{h})=F_0(\mathbf{h}{)}^{\ast }$, hence $I(\overline{222})=13130$.

With anomalous scattering the atomic imaginary term retains its sign when the reflection index reverses. Here $\Delta F(-222)=19.2i$, soThus the second expected intensity is approximately $1.157\times 10^4{\mathrm{electrons}}^2$. Conjugating the complete anomalous structure factor would incorrectly impose Friedel equality on the second experiment.