GENERAL REMARKS REGARDING ELEMENTS. 125 

 III. 



Classification of elements may be based upon either physical or 

 chemical properties, or upon a consideration of both. A natural 

 classification of all elements is the one dividing them into two groups 

 of metals and non-rnetals. 



Metals are all elements which have that peculiar lustre known as 

 metallic lustre ; which are good conductors of heat and electricity ; 

 which, in combination with oxygen, form compounds generally 

 showing basic properties ; and which are capable of replacing hy- 

 drogen in acids, thus forming salts. 



Non-metals or metalloids are all elements not having the above- 

 mentioned properties. Their oxides in combination with water gen- 

 erally have acid properties. In all other respects the chemical and 

 physical properties of non-metals differ widely. Their number 

 amounts to 18, the other 58 elements being metals. 



Natural groups of elements. Besides classifying all elements 

 into metals and non-metals, certain members of both classes exhibit 

 so much resemblance in their properties, that many of them have 

 been arranged into natural groups. The members of such a natural 

 group frequently show some connection between atomic weights and 

 properties. 



Chlorine, 35.2 Sulphur, 31.8 Lithium, 7.0 Calcium, 39.8 

 Bromine, 79.3 Selenium, 78.6 Sodium, 22.9 Strontium, 86.9 

 Iodine, 125.9 Tellurium, 126.6 Potassium, 38.8 Barium, 136.4 



Each three elements mentioned in the above four columns resemble 

 each other in many respects, forming a natural group. The relation 



