Chemical and Physical Properties of Elements. 27 



is non-metallic, very stable under ordinary conditions, and its 

 atom-fixing power is four. Oxygen is gaseous, chemically 

 active, but electronegative, and its atomicity is two. Fluorine 

 is in all probability- gaseous: it is chemically active, so much 

 so that it has never been isolated, powerfully electronegative; 

 and its atomicity is one. At this point the character of the 

 elements suffers an abrupt change: and the next element 

 (sodium) is a metal of the alkalies, and almost exactly repeats 

 the properties of lithium. After sodium, as after lithium, 

 come six elements, at small intervals of atomic weight ; and 

 they repeat the changes and transitions that take place in the 

 elements succeeding lithium. There is, first, magnesium, a 

 metal of the alkaline earths: and then an earth-metal (alumi- 

 nium), triad like boron. Xext comes silicon, analogous in so 

 many respects to carbon, being neither strongly electropositive 

 nor strongly electronegative, and having also an atomicity of 

 four. Then comes sulphur, electronegative, but less so than 

 oxygen, but with analogous properties in many respects. 

 Chlorine (gaseous, electronegative, and a monad) is like fluo- 

 rine repeated in a modified form; and then again comes an 

 abrupt change, and an alkali metal (potassium) succeeds. 

 Thus we recognize a periodicity in atomic functions corre- 

 sponding to intervals of seven elements, and to increase of 

 sixteen in atomic weight. 



Potassium and the six succeeding elements form another 

 period, but repeat less distinctly the typical characters of the 

 first periods. There is the same transition from alkali metal 

 to alkaline-earth metal (calcium), from low to high atomicity; 

 and from highly positive elements to the elements chromium 

 and manganese, which, although possessed of basylous pro- 

 perties, have also well-marked chlorous characteristics. But 

 it is evident that potassium and the six elements in succession 

 fail to repeat the full periodic change from alkali metal to 

 alkali metal ; there is not the complete transition from posi- 

 tive to negative, and again to positive : nor from low atomi- 

 city to high, and again to low. The three elements succeeding 

 to manganese form with it and with copper, which they serve 

 to link together, the iron group, which exhibits within itself 

 so many interesting relations of resemblance and difference. 

 Copper has long been held to have strong affinities with 

 sodium; and it is similar, among other things, in being the 

 first of a series of seven exhibiting the periodic change. For 

 although copper is not a monad, like sodium, the atomicity 

 has fallen rapidly from manganese ; and although it is not 

 intensely active, like sodium, it is metallic and electropositive, 

 and has no symptoms of chlorosity. Zinc, the next element, 



