Boron/aluminium connectivities

Mendeleev s real insight was revealed in his 1871 paper in connection with vacant spaces in the periodic table. He gave the provisional names eka-aluminium, eka-boron and eka-silicon [to the elements he expected to fill these gaps], (Ihde, 1964, p. 283)... 

The most striking facts concerning this group are in connection with the abundance of the elements. Aluminium is the most abundant metal and the third most abundant element that we know, making up 7.28 per cent1 of the world which we are able to examine. With the exception of boron nil the other elements of this group are scarce, and some of them are among the least common of all the elements of the periodic table. 

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