Questions about elements of group 18 (group 0 in old notation) of the periodic table and their compounds, created despite the low reactivity of these elements.

Reactivity of noble gases rises with the size of their atoms along with polarisability. Xenon has several known compounds, krypton significantly less and argon only a few. Neon and helium have no "true" compounds, but their protonated forms, excimers, and van der Waals molecules are known.

The name "noble gases" is IUPAC approved and it currently consists of the elements helium $\ce{He}$, neon $\ce{Ne}$, argon $\ce{Ar}$, krypton $\ce{Kr}$, xenon $\ce{Xe}$ and radon $\ce{Rn}$. (compare IUPAC Red Book 2005, IR-3.5)

$$ \scriptstyle\Tiny \begin{array}{l|cccccccccccccccccc} \text{Gr.} &1 &2 &3 &4 &5 &6 &7 &8 &9 &10 &11 &12 &13 &14 &15 &16 &17 &18\\ \text{Per.}\\\hline 1& \ce{^1H} & &&&&&&&&&&&&&&&&\color{\red}{\ce{^2He}}\\ 2& \ce{^3Li}& \ce{^4Be}& &&&&&&&&&&\ce{^5B}& \ce{^6C}& \ce{^7N}& \ce{^8O}& \ce{^9F}& \color{\red}{\ce{^{10}Ne}}\\ 3& \ce{^{11}Na}& \ce{^{12}Mg}& &&&&&&&&&&\ce{^{13}Al}& \ce{^{14}Si}& \ce{^{15}P}& \ce{^{16}S}& \ce{^{17}Cl}& \color{\red}{\ce{^{18}Ar}}\\ 4& \ce{^{19}K}& \ce{^{20}Ca}& \ce{^{21}Sc}& \ce{^{22}Ti}& \ce{^{23}V}& \ce{^{24}Cr}& \ce{^{25}Mn}& \ce{^{26}Fe}& \ce{^{27}Co}& \ce{^{28}Ni}& \ce{^{29}Cu}& \ce{^{30}Zn}& \ce{^{31}Ga}& \ce{^{32}Ge}& \ce{^{33}As}& \ce{^{34}Se}& \ce{^{35}Br}& \color{\red}{\ce{^{36}Kr}}\\ 5& \ce{^{37}Rb}& \ce{^{38}Sr}& \ce{^{39}Y}& \ce{^{40}Zr}& \ce{^{41}Nb}& \ce{^{42}Mo}& \ce{^{43}Tc}& \ce{^{44}Ru}& \ce{^{45}Rh}& \ce{^{46}Pd}& \ce{^{47}Ag}& \ce{^{48}Cd}& \ce{^{49}In}& \ce{^{50}Sn}& \ce{^{51}Sb}& \ce{^{52}Te}& \ce{^{53}I}& \color{\red}{\ce{^{54}Xe}}\\ 6&\ce{^{55}Cs}& \ce{^{56}Ba}& \text{*}& \ce{^{72}Hf}& \ce{^{73}Ta}& \ce{^{74}W}& \ce{^{75}Re}& \ce{^{76}Os}& \ce{^{77}Ir}& \ce{^{78}Pt}& \ce{^{79}Au}& \ce{^{80}Hg}& \ce{^{81}Tl}& \ce{^{82}Pb}& \ce{^{83}Bi}& \ce{^{84}Po}& \ce{^{85}At}& \color{\red}{\ce{^{86}Rn}}\\ 7& \ce{^{87}Fr}& \ce{^{88}Ra}& \text{**}& \ce{^{104}Rf}& \ce{^{105}Db}& \ce{^{106}Sg}& \ce{^{107}Bh}& \ce{^{108}Hs}& \ce{^{109}Mt}& \ce{^{110}Ds}& \ce{^{111}Rg}& \ce{^{112}Cn}& \ce{^{113}Nh}& \ce{^{114}Fl}& \ce{^{115}Mc}& \ce{^{116}Lv}& \ce{^{117}Ts}& \ce{^{118}Og}\\\hline \end{array}\\ \scriptstyle\Tiny \begin{array}{lc} \text{* Lanthanoid}& \ce{^{57}La}& \ce{^{58}Ce}& \ce{^{59}Pr}& \ce{^{60}Nd}& \ce{^{61}Pm}& \ce{^{62}Sm}& \ce{^{63}Eu}& \ce{^{64}Gd}& \ce{^{65}Tb}& \ce{^{66}Dy}& \ce{^{67}Ho}& \ce{^{68}Er}& \ce{^{69}Tm}& \ce{^{70}Yb}& \ce{^{71}Lu}\\ \text{** Actinoid}& \ce{^{89}Ac}& \ce{^{90}Th}& \ce{^{91}Pa}& \ce{^{92}U}& \ce{^{93}Np}& \ce{^{94}Pu}& \ce{^{95}Am}& \ce{^{96}Cm}& \ce{^{97}Bk}& \ce{^{98}Cf}& \ce{^{99}Es}& \ce{^{100}Fm}& \ce{^{101}Md}& \ce{^{102}No}& \ce{^{103}Lr} \\ \end{array} $$

Further reading