CHAPTER XVII 

 THE HALOGEN FAMILY 



THE elements, if we may judge from those studied or mentioned 

 thus far, may be divided into two classes the metallic or positive 

 elements, like sodium, zinc and magnesium, and the non-metallic 

 or negative elements, like oxygen, chlorine and sulphur. The 

 former give positive ions, such as Na+, Mg++. The latter give 

 negative ions, such as Cl~, S = . Hydrogen constitutes the single 

 exception, giving the positive ion H + . 



Natural Families of Elements. We have a simple means 

 of subdividing within each of these two classes. We can place 

 together the elements of like chemical behavior. Thus sodium 

 and potassium or zinc and magnesium resemble one another 

 very closely in their reactions. Also, oxygen and sulphur form 

 one group and chlorine, bromine, iodine and fluorine form an- 

 other. Groups of this kind are often spoken of as natural fami- 

 lies of elements. The last group is called the halogen family, 

 from the Greek for salt-producing, because these elements com- 

 bine with sodium to give substances all resembling common 

 salt. (Usually, the elements of one family and their correspond- 

 ing compounds resemble one another in a number of ways, and 

 show at the same time a gradation in properties which it is in- 

 teresting to study .^) 



BROMINE Br 2 



The element was discovered by Balard in 1826 and derives its 

 name from its offensive odor (Greek, a stench). 



Preparation. The salt deposits and natural salt wells of 

 Cheshire, of Germany, and of Michigan, West Virginia, Ohio, and 



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