Chemical Molecules 



it can directly unite is strictly limited. All atoms 

 of the same element have the same valency. 

 Monovalent atoms are those which can, under no 

 circumstances, unite with more than one other 

 atom. The Hydrogen atom is an example of 

 such an atom. Divalent atoms, as, for example, 

 that of Oxygen, can unite with one other atom of 

 similar valency or with two monovalent atoms. 

 Similarly, a trivalent atom, such as that of 

 Nitrogen, can unite with three monovalent 

 atoms. A tetravalent atom, such as that of 

 Carbon, can combine with four monovalent 

 atoms. There are also pentavalent and hexa- 

 valent atoms. Now, by indicating the valency 

 of any given atom by a stroke for each mono- 

 valent atom with which it is able to combine, 

 chemists have been able to represent the mole- 

 cule of every compound, or, at any rate, of every 

 inorganic compound, by what is known as a 

 graphic or structural formula. Thus, ethylic 

 alcohol is represented by the formula : 

 H H 



H C C O H = C 2 H 6 0, 



H H 



and methylic ether by the structural formula : 

 H H 



H C O C H = C 2 H 6 0. 



A A 



