LAWS AND THEORIES OF CHEMISTRY. 103 



liarity in the power of attraction of different elements toward other 

 elements, and to this property of the atoms of elements of holding 

 in combination one, two, three, four, or more atoms of other ele- 

 ments the name atomicity, quantivalence, or simply valence, has been 

 given. 



According to this theory of the valence of atoms, we distinguish 

 univalent, bivalent, trivalent, quadrivalent, quinquivalent, sexivalent, 

 and septivalent elements. All elements which combine with hydro- 

 gen in the proportion of one atom to one atom are univalent, as, for 

 instance, Cl, Br, I, F, and all elements which combine with these in 

 but one proportion, that is, atom with atom, bear the same valence, 

 or are also univalent, as, for instance, Na, K, Ag, etc. 



Those elements which combine with hydrogen or other univalent 

 elements in the proportion of one atom to two atoms are bivalent, 

 such as O, S, Se. 



Trivalent and quadrivalent elements are those the atoms of which 

 combine with 3 or 4 atoms of hydrogen, respectively. Figuratively 

 speaking, we may say that the atoms of univalent elements have but 

 one, those of bivalent elements two, of trivalent elements three, of 

 quadrivalent elements four bonds or points of attraction, by means of 

 which they may attach themselves to other atoms. 



Elementary atoms are often named according to their valence : 

 monads, diads, triads, tetrads, pentads, hexads, and heptads. 



To indicate the valence of the elements frequently dots or numbers 

 are placed above the chemical symbols, thus H 1 , O u , N m , C mi or C iv . 



The bonds are often graphically represented by lines, thus : 



H-, -0-, -N-, -0- 



It is needless to say that such representations are merely symbolical, 

 and express the view that atoms have a definite power to combine 

 with others. 



When atoms combine with one another the bonds are said to be 

 satisfied, and it is graphically expressed thus : 



I / 



-N- 



H Cl, H O H or O , H-N-H or N-H 



XH \ H 



While the valence of some elements is invariably the same under 

 all circumstances, other elements show a different valence (this means 

 a different combining power for other atoms) under different condi- 



