Fluorine
It is krypton as it the far most right on the periodic table, having the smallest radius
Argon doesnt have the smallest atomic radius, its chlorine.Argon has the largest atomic radius in period 3.
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It is helium that has the smallest atomic radius. Use the link below to see a list of elements arranged by atomic radius.
atomic radius increases as you go down the group and decreases as you go across the period therefore the smallest atomic radius for group 14 is carbon.
It is hydrogen.
Potassium is the period four element with the lowest mass; its average mass is 39.0983amu.
Helium usually is listed with the smallest atomic radius when calculated. Hydrogen however has a smaller van der Waals radius The protium isotope of hydrogen has the smallest nucleus radius. It is 1.6 fm
Rubidium
Argon is the atom that has the smallest radius in Period 3. As you go cross Period 3 from left to right, the atomic radii of the elements decrease. The elements in Period 3 from left to right begin with sodium and ends with argon.
Atomic Radius gets greater down the periodic table and gets smaller to the right in the periodic table. This means, in order of atomic radius, that the five smallest elements are Helium, Neon, Fluorine, Oxygen, and Hydrogen in that order. Check all of it out at http://www.ptable.com/ under properties>radius
Phosphorus (1.23 Å) has an atomic radius smaller than that of tellurium (1.42 Å).