Guessing its H+
Helium has the smallest covalent radius
It is hydrogen.
The radius of an anion is bigger than the radius of a neutral atom.
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
Francium. The elements of the lower left hand side of the periodic table have the largest atomic radius. The upper right has the smallest.
Helium has the smallest covalent radius
The smallest anionic radius is typically found on the right side of the periodic table in the halogen group (Group 17). This is because anions gain electrons to achieve a stable electron configuration, leading to a decrease in the atomic radius.
It is helium that has the smallest atomic radius. Use the link below to see a list of elements arranged by atomic radius.
Fluorine
It is hydrogen.
The element with the smallest negative ionic radius is fluorine (F). It has a small ionic radius due to the high effective nuclear charge, which attracts the electrons closer to the nucleus in the ionic form.
The radius of an anion is bigger than the radius of a neutral atom.
Helium usually is listed with the smallest atomic radius when calculated. Hydrogen however has a smaller van der Waals radius
If you are talking about individual atoms, it is hydrogen by mass or helium by radius.
nitrogen
The period 4 element with the smallest atomic radius is chlorine, which has a greater number of protons in the nucleus pulling the electrons closer, making it smaller compared to other elements in the same period.
Fluorine has the smallest atomic radius among fluorine, chlorine, bromine, iodine, and astatine.