Here is another way to consider the same scheme. The inert elements appear at the end of either the first two, an eight, a six. Wherever there is the six of a p subshell there is the two of an s subshell above it to make eight electrons in the outer full shell of a noble gas. The electron configuration for xenon is:
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6