ELEMENTS AND COMPOUNDS 1 7 



will be required to combine with i atom of carbon, hav- 

 ing a valence of 4. The formula is CO 2 . In the for- 

 mulas of compounds, the valences of the atoms uniting 

 are always balanced or satisfied. 



When two elements combine, and one of them has an 

 odd valence, as phosphorus, which has a valence of 3, 

 two atoms of the element with the odd valence are always 

 required for combination. For example, two phosphorus 

 atoms, each having a valence of 3, making a total valence 

 of 6, require, in order to combine with O, whose valence 

 is 2, three atoms of O, which make the valence of 6. The 

 two atoms of phosphorus combine with the three atoms 

 of oxygen, making a balanced compound, and the va- 

 lences of the phosphorus and oxygen are satisfied. The 

 compound is P 2 O 3 . 



Combine according to the lowest valence, the following 

 elements, and give the formulas of the compounds pro- 

 duced. 



Zinc and oxygen 2s>\ Sulfur and oxygen 



Calcium and oxygen C, . Sodium and chlorin 

 Tin and oxygen $L Potassium and chlorin 



Iron and oxygen Carbon and oxygen 



Potassium and oxygen Phosphorus and oxygen 



Silicon and oxygen Iron and sulfur 



Potassium and sulfur 

 Manganese and sulfur 

 Phosphorus and hydrogen 

 Calcium and chlorin 

 Aluminum and oxygen 

 Phosphorus and oxygen 



Problem i. How much hydrogen is required to combine with 20 

 grams of O to form H 2 O ? When hydrogen and oxygen unite to 

 form water, the combination takes place according to valence, as 



