radiiXML =
Import["https://en.wikipedia.org/wiki/Atomic_radii_of_the_elements_(data_\
page)", {"HTML", "XMLObject"}];
<< XMLGraph`
g = XMLGraph[radiiXML]
Values[g@"Children"[g@"Select"[".wikitable td"]]][[2 ;; ;; 9]]
{{"H"}, {"He"}, {"Li"}, {"Be"}, {"B"}, {"C"}, {"N"}, {"O"}, {"F"}, {"Ne"}, \
{"Na"}, {"Mg"}, {"Al"}, {"Si"}, {"P"}, {"S"}, {"Cl"}, {"Ar"}, {"K"}, {"Ca"}, \
{"Sc"}, {"Ti"}, {"V"}, {"Cr"}, {"Mn"}, {"Fe"}, {"Co"}, {"Ni"}, {"Cu"}, \
{"Zn"}, {"Ga"}, {"Ge"}, {"As"}, {"Se"}, {"Br"}, {"Kr"}, {"Rb"}, {"Sr"}, \