50 ILLINOIS STATE ACADEMY OF SCIENCE 



having eleven positive charges upon its nucleus, two elec- 

 trons close to the nucleus, eight more outside of these 

 two, and the one valence electron still outside these eight 

 forming the beginning of a new shell of outer or valence 

 electrons. The second row in the periodic table thus be- 

 comes a repetition of the first row, the number of valence 

 electrons increasing with the atomic number until we 

 reach the rare gas argon, the only difference being that 

 the second row has an inner shell of eight electrons The 

 chemical properties of these elements bear out this con- 

 clusion absolutely. If time permitted, we could go on 

 through the periodic table of elements, showing how the 

 properties of these elements may be explained by as- 

 suming that the electrons are arranged in series of shells, 

 one about the other, the outer shell always composed of 

 the valence electrons. 



Since this group of eight seems to be a peculiarly stable 

 arrangement for the electrons about an atom, Ave should 

 expect that those atoms which have less than eight elec- 

 trons in their outer shells would try to acquire eight 

 electrons when they enter into a chemical compound. 

 This proves to be the case. It does not apply, of course, 

 to those atoms which are relatively weak, that is, those 

 atoms which have a small positive charge upon the nu- 

 cleus, because we have seen that when they enter into 

 chemical combination they lose their valence electrons 

 entirely. But, for the atoms beginning with carbon, 

 which do not lose their valence electrons to another atom 

 in a chemical combination, we. find in a vast majority of 

 cases they combine with other atoms in such a way that 

 they complete their shell of valence electrons up to the 

 number eight. An inspection of such typical compounds 

 as carbon tetrafluoride, methane, ammonia, water and 

 hydrogen fluoride, will show that this is the case. The 

 hydrogen atom, it may be remarked here, with only one 

 positive charge upon its nucleus and only one electron of 

 any kind, appears to be completely satisfied with two 

 electrons instead of eight. But this is what we might ex- 

 pect since we have been led to the conclusion that all 

 atoms have two electrons arranged very close to the nu- 

 cletis. Hydrogen and helium with atomic numbers of one 



