Explain the measurement methods of atomic radius.

(N/A) There is no direct method to measure the absolute size of an individual atom.
The size of an atom is extremely small,approximately $1.2 \ \mathring{A}$ (i.e.,$1.2 \times 10^{-10} \ m$).
Since the electron cloud surrounding the nucleus does not have a sharp,well-defined boundary,the determination of an exact atomic size is not possible.
Consequently,there is no practical way to measure the size of an isolated atom.
Instead,atomic radius is defined as covalent or metallic radius,which is determined experimentally using techniques such as $X$-ray diffraction or spectroscopic methods.