• Na atoms are larger than Cl atom because as we go left to
right in a series, size of atoms decreases. This is because of
increase in number of electrons and protons in the same shell.
Na ( Z= 11) : 1s2 2s2 2p6 3s1
Cl ( Z= 17) : 1s2 2s2 2p63s2 3p7
Na and Cl both are atoms of 3rd period , but in case of Cl
number of protons increases in the nucleus than Na , so electron
cloud of Cl is pulled more tightly in Cl. Thus size of Na is
greater than Cl.
• Na is larger than Na+ because size of a cation is always
smaller than its parent atom because losing an electron will
decrease the electron/proton ratio and it will result in increase
in effective nuclear charge. Thus electron cloud is pulled more
here and we can say size decreases in cation than parent atom.
• similarly Cl+ (cation) is smaller than Cl ( parent Atom) . So
Cl+ is also smaller than Na because Na is larger than Cl.
Hence Na has largest atomic radius.