`Combining Elements to Form a CompoundJudith Brakes                  Byrd Academy                               363 W. Hill St.                               Chicago, Illinois 60610                               312-280-4000Objectives: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 tubeswater                     beakers                 test tube standsRecommended 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.`