Chemical Change and Energy 311 



of chlorine (Cl), held fast together in some way which 

 we do not entirely understand. 



The smallest particle of an element is called an atom. 



The smallest particle of a compound is called a mole- 

 cule. 



Molecules are usually made of two or more atoms 

 joined together. 



Application 68. In the following list tell which things are 

 elements, which are compounds, and which are mixtures, 

 remembering that both solutions and alloys are mixtures : 



Air, water, salt, gold, hydrogen, milk, oxygen, radium, 

 nitrogen, sulfur, baking scda, sodium, diamonds, sweetened 

 coffee, phosphorus, hydrochloric acid, brass. 



Inference Exercise 



Explain the following : 



431. Although in most electric lamps there is a vacuum between 



the glowing filaments and the glass, the glass nevertheless 

 becomes warm. 



432. Clothes left out on the line overnight usually become 



damp. 



433. You can separate water into hydrogen and oxygen, yet you 



cannot separate the hydrogen or the oxygen into any 

 other substances. 



434. Wet paper tears easily. 



435. Windows are soiled on the outside much more quickly in 



rainy weather than in clear weather. 



436. If you stir iron and sand together, the iron will rust as if 



alone. 



437. Rust is made of iron and oxygen, yet you cannot separate 



the iron from the oxygen with a magnet. 



438. A reading glass helps you to read fine print. 



439. Stretching the string of a musical instrument more tightly 



makes the note higher. 



440. Mayonnaise dressing, although it contains much oil, can 



readily be washed off a plate with cold water. 



