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Our Surroundings 



Many elements such as gold, platinum, radium and helium, 

 are found only in small quantities. For this reason they are 

 called rare. The number of elements of which common things 

 are composed is less than one-fifth of the elements known. Among 

 those most widely distributed and which form the greatest part 

 of the earth's crust are oxygen, silicon, iron, aluminum, calcium, 

 magnesium and potassium. All living things are made up largely 

 of carbon, hydrogen, oxygen and nitrogen. 



Compounds and Mixtures. All substances are classed as 

 (1) elements, (2) compounds, or (3) mixtures. A compound is a 

 chemical union of two or more elements, a union in which each 

 element loses its own properties and helps form a new substance 

 having entirely different properties. The gases oxygen and hydro- 

 gen unite chemically and form a liquid, water. Water is a 

 compound. 



A mixture is a physical union of two or more substances 

 which do not lose their properties by uniting. What is known 

 as a solution is also a mixture. A cup of sweetened coffee is a 

 solution or a mixture, but not a compound. In it there are 



