THE MORE COMMON ELEMENTS AND COMPOUNDS 15 



Iron and manganese are alike peculiar, with a valence of 2, 3, 6, 

 or 7. 



Aluminum is a trivalent element with three-handed atoms, 

 while nitrogen and phosphorus may use either three or five 

 bonds. 



This leaves only the strictly tetravalent family, carbon (= C = ), 

 sil icon ( = Si = ) , and titanium ( =Ti = ) .* 



When an iron atom uses three hands, it is called -ic iron, but if it 

 uses only two hands it is called -ous iron. Thus we have the ferrous 

 chlorid (FeCl 2 ) and ferric chlorid (FeCl 3 ) ; also ferrous oxid (FeO) 

 and ferric oxid (Fe 2 O 3 ). Likewise, when phosphorus uses only 

 three bonds, it is called -ous phosphorus, but with the five bonds 

 in use it is -ic phosphorus, as in phosphorous chlorid (PC1 3 ) and 

 phosphoric chlorid (PC1 5 ), which are also called phosphorus tri- 

 chlorid and phosphorus pentachlorid, the endings, -ous and -ic, 

 being unnecessary when the valence is specified in the number of 

 chlorin atoms held. 



Matter may exist in three distinctly different forms or classes 

 which might be called " wonary " (single), "fo'nary" (double), and 

 " trinary," or ternary (triple). 



First, matter may exist in the form of free or uncombined ele- 

 ments; as solid metallic iron, aluminum, magnesium, calcium, 

 sodium, or potassium; as solid nonmetallic carbon, phosphorus, 

 sulfur, or silicon; as liquid mercury or bromin; or as gaseous 

 oxygen, nitrogen, hydrogen, or chlorin. This might be termed 

 the " wonary " form, all atoms in the molecule being of the one 

 element. 



Second, matter may exist in binary compounds ; that is, with 



1 Argon is of interest chiefly because it is so very common and yet so recently 

 discovered. Argon is everywhere present in the air and we respire more than an 

 ounce a day of that element. It is an invisible gas, and because it is mixed with so 

 much nitrogen (which it resembles somewhat) and oxygen, and cannot be seen, 

 it would be less easily discovered than many other elements; but the chief rlimculty 

 in detecting it by chemical methods was due to its chemical inaction. Because of this 

 inaction, it has been named argon, which means without action. When the ele- 

 ment was discovered and very thoroughly investigated, the discoverers (Rayleigh 

 and Ramsay, in 1894) concluded that the argon atom has no valence, no hand with 

 which to clasp the hand of another atom, either of argon or of any other element. 

 In other words, they discovered that argon forms no compounds, and that the 

 molecule of argon is monatomic (man or mono means one, as in monotone = one 

 tone). Later investigations indicate, however, that argon has some weak affinities. 



