18.1 The discovery of the rare gases 18.4 The rare gas compounds 18.3 The existence and recovery of the rare gases 18.2 Properties and uses of the rare gases 18.5 Summarry on the main group elements
15.5 The compounds of As, Sb and Bi 15.4 The compounds of phosphorus 15.3 The compounds of nitrogen 15.2 The elemental substances of nitrogen family 15.1 Outline on nitrogen family
14.5 The compounds of tin and lead 14.4 The compounds of silicon 14.3 The compounds of carbon 14.2 The elemental substances of carbon family 14.1 Outline on carbon family