Question

Which one has the bigger size?
(i) Na or Cl
(ii) Cl or F

Answer 1

A chemical element's atomic radius is a measurement of the size of its atoms, generally the mean or normal distance between the nucleus's centre and the border of the surrounding electron shells. There are numerous non-equivalent definitions of atomic radius since the border is not a well-defined physical object.

Complete answer:
The size of Na (sodium) is larger than that of Cl (chlorine). Both Na and Cl belong to the same period (3rd period), and the atomic size generally decreases across the period because the outer electrons are in the same Valence shell within the period, and the effective nuclear charge increases as the atomic number increases, resulting in increased attraction of electrons to the nucleus on moving leptons. As a result, from Na to Cl, the size shrinks.
Because the effective nuclear charge rises from left to right in a period, Na has a larger size than Cl. The electronegativity of the nucleus increases as a result of this effective nuclear charge, as does the nucleus's attraction to valence shell electrons. As a result, the atom's size shrinks.
Cl is somewhat larger than F. Cl and F are both members of the same family (Group-17). The main quantum number (n) of halogens grows as we proceed down the group, and the valence electrons migrate further away from the nucleus. This occurs because the inner energy levels are packed with electrons, which serve to shelter the outer electrons from the nucleus's attraction, resulting in a larger size. Because the number of shells rises as you move along a group, Cl is larger than F. As a result, the size of an atom grows as it moves along a group.

Note:
Electrons lack fixed orbits and well defined ranges. Instead, their locations must be represented as probability distributions that taper off gradually as one travels out from the nucleus, with no sudden cutoff; these are known as atomic orbitals or electron clouds. Furthermore, in condensed matter and molecules, atoms' electron clouds frequently overlap, and some electrons may travel across a broad range covering two or more atoms.