42 



A. W. Stejvart on 



masses and occupy definite volumes, so that we speak of the 

 'atomic weight" and the "atomic vohmie " of an element. 



Tn 1815 Prout suggested that the atoms of all elements are 

 built up from those of hydrogen, which is the lightest known 

 body. For almost a century Front's views were rejected by the 

 scientific world, but recent work tends to establish this hypothesis 

 upon a more solid basis. 



Towards the classification of these ninety-two elements the 

 earliest definite work was due to the English chemist, Newlands, 

 while at a later date, and apparently independently, Mendcleef 

 and Lothar Meyer developed the system into its present form. 



Suppose that the elements are arranged in ascending order 

 of the weights of their atoms, and that alongside the names of 

 the elements we place first the nature of the element and second 

 the number of hydrogen atoms which one atom of the element 

 will combine with or will displace from combination. We then 

 get the following arrangement : — 



Table I. 



Atoniio Weiglit 

 oorreot to the 

 nearest unit. 



Element. 



Nature of Element. 



Number of Hydrogen 



Atoms combined with 



or displaced by one 



atom of the element. 



*Helium 

 **Lithium 

 ***Beryllium 

 Boron 

 Carbon 

 Nitrogen 

 Oxygen 

 Fluorine 

 *Neon 

 **Sodium 

 "^■^^Magnesiun 



Inert gas 



Light soft metal 1 



Heavier tough metal 2 



Non-metal 3 



Non-metal 4 



Gas, not reactive .3 

 Gas, reactive 

 Gas, very reactive 

 Inert gas like helium 

 Metal like lithium 



Metal like beryllium 2 



An examination of the above Table brings to light a certain 

 order in the arrangement. Thus helium, the first element, has 



properties similar to those of the ninth element, neon ; the second 



