How is the size of an atom indicated ?

(a) How does the size of atoms (atomic size) generally vary in ging from left to right in a period of the periodic table? Why does it vary this way? (b) What happens to the metallic character of the elements as we move from left to right in a period of the periodic table?

For all practical purposes, the size of an individual atom cannot be uniquely defined. An indirect approach is required. The size of an atom is determined by its immediate environment, especially its interaction with surrounding atoms. Pertaining to the types of bonding how many types of atomic radii are employed?

The size of atomic nucleus is