Combining Elements to Form a Compound

Judith Brakes                  Byrd Academy
                               363 W. Hill St.
                               Chicago, Illinois 60610
                               312-280-4000

Objectives:

Grade 4-6, 2 day activity.

1. The student will understand that when two elements are combined, they form a 
   compound.
2. When observing a test tube containing steel wool, after 24 hours, the 
   student will be able to explain the rust on the steel wool as a new compound 
   which was formed from the combination of oxygen and steel.

Materials:

rubber bands              steel wool              test tubes
water                     beakers                 test tube stands

Recommended strategies:

 Students will work in groups of 2-3.
     First try a simple experiment.  Write the numbers 0-9 on the blackboard.  
Tell the students to make combinations of these numerals, for example 12, 45, 
360, and 4679.  Ask the students to see how many combinations of the digits 0-9 
they can write in 30 seconds.  They can use individual digits more than once and 
the number can have up to four digits.  This activity will help demonstrate how 
many combinations of elements there can be. 
     Explain that there are over 100 elements that man has been able to 
identify.  Elements are combined just as the students combined the digits 0-9.  
The digits are like elements.  Unlike the numbers, though, not all elements can 
be combined with other elements, and the ways in which they can be combined are 
limited.  However there are millions of different compounds that can be made by 
combining two or more elements. 
     Students will now learn how two elements combine to form a compound.  Place 
a piece of steel wool, about the size of a marble, in each test tube.  Use a 
pencil to push the steel wool to the bottom of the tube.  Pour some water in and 
out of the test tube to wet the steel wool.  Stand the test tubes on the test 
tube rack for 24 hours.  
     Students shall discuss the change in the appearance of the steel wool.  
They should notice rust on the steel wool.  The water level in the test tube 
should also have risen because when an element is combined with oxygen the new 
element takes up more space.
     
References:

Elementary Science Learning by Investigating, Level 5. Chicago: Rand McNally, 
1975. 

Science Connections. Columbus, Ohio:Merrill, 1990.