--------+-----------+-----------+-----------+-----------+ Periods | GROUP | GROUP | GROUP | GROUP | | V | VI | VII | VIII | |A B|A B|A B| | --------+-----------+-----------+-----------+-----------+ 1 | | | | | 2 |N=14.04 |O=16 |F=19 | | --------+-----------+-----------+-----------+-----------+ 3 | P=31| S=32.06| Cl=35.45| | --------+-----------+-----------+-----------+-----------+ 4 |V=51.2 |Cr=52.1 |Mn=55 |Fe=55.9 | | | | |Ni=58.7 | | | | |Co=59 | --------+-----------+-----------+-----------+-----------+ 5 | As=75| Se=79.2| Br=79.96| | --------+-----------+-----------+-----------+-----------+ 6 |Cb=94 |Mo=96 | |Ru=101.7 | | | | |Rh=103 | | | | |Pd=106.5 | --------+-----------+-----------+-----------+-----------+ 7 | Sb=120.2| Te=127.6| I=126.97| | --------+-----------+-----------+-----------+-----------+ 8 |Ta=183 |W=184 | |Os=191 | | | | |Ir=193 | | | | |Pt=194.8 | --------+-----------+-----------+-----------+-----------+ 9 | | | | | --------+-----------+-----------+-----------+-----------+ 10 | U=238.5 | | | | --------+-----------+-----------+-----------+-----------+ | R_{2}O_{5}| RO_{3} | R_{2}O_{7}| RO_{4} | | RH_{3} | RH_{2} | RH | | --------+-----------+-----------+-----------+-----------+ [* This includes a number of elements whose atomic weights lie between 140 and 173, but which have not been accurately studied, and so their proper arrangement is uncertain.] ~Place of the atmospheric elements.~ When argon was discovered it was seen at once that there was no place in the table for an element of atomic weight approximately 40. When the other inactive elements were found, however, it became apparent that they form a group just preceding Group 1. They are accordingly arranged in this way in Group 0 (see table on opposite page). A study of this table brings to light certain very striking facts.