How is atomic size actually determined? Is it the number of protons + neutrons or the no. of electron shells?

Atomic size is empirically determined by x-ray crystal structure. How far apart are bonded atoms in the element? In compunds?



From theory, atom size is typically the 90% probability envelope of electron distribution.

How is atomic size actually determined? Is it the number of protons + neutrons or the no. of electron shells?
The Atomic Number is the number of Protons in the Nucleus, the number of Neutrons determines the isotope.
Reply:by x ray difraction instruments. the size is not the number of protons + neutrons or the no. of electron shells. the size is an average of the radius of covalent bonding in their diatomic structure.
Reply:The atomic radius includes the electron shells. You raise a good point because some of the orbitals theoretically go out to infinity. So the convention is to look at a 90% probability level for the size of the electron shells.

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