Part A Counting Atoms
 The formula for a compound indicates the elements that make up the compound and the number atoms of each element present in the compound.  These numbers atoms are indicated by the use of small numbers called subscripts.  Sometimes a groups of atoms act as a single atom.  Such a group of atoms is called a polyatomic ion.  If a polyatomic ion is used in a formula more than once, it is put in parentheses and the subscript appears outside the parentheses.  When a subscript  appears outside the parentheses, it indicates that all the elements inside the parentheses should be multiplied by that subscript.  For the example, the formula Fe(OH)3 indicate the combination of 1 atom of iron Fe, 3 atoms of oxygen, O and 3 atoms of hydrogen H

 In the following examples, list each elements in the compound and the number of atoms of each elements present.  The first example has been done for you.  You may already be familiar with some of the compounds. You should also complete the other blank on the chart.

 

Name	Use	Formula	Atoms in Formula
Calcium carbonate	Limestone	CaCO3	Ca = calcium 1  C = carbon 1  O = oxygen 3
Aspirin	pain reliever	C9H8O4	.
Magnesium hydroxide	.	Mg(OH)2	.
Paradichlorobenzene	moth crystals	C6H4Cl2	.
.	Found in vinegar	C2H4O2	.
Trinitrotoluene (TNT)	.	C7H5(NO2)3	.
Calcium dihydrogen phsophate	Fertilizer	Ca(H2PO4)2	.
Pyrite	.	FeS2	.
.	Sugar	C12H22O11	.
Heptane	One of several componenets in gasoline	C5H12	.
Sulfuric acid	.	H2SO4	.
Cellulose	.	C6H702(OH)3	.
Asbestos	.	H4Mg3Si2O9	.
Dichlorodiphenyl  trichloroethane (DDT)	Banned pesticide	C13H9Cl5	.
Silicon dioxide	.	SiO2	.
Iron oxide	.	Fe2O3	.
Butane	.	C4H10	.

 
 
 

Part B Compounds

Vocabulary Skills: applying definitions

    On the diagram below, label correctly each of the following:
            chemical formula                   chemical equation
            subscript                        coefficient
 
 
 

2 H2   +   O2   ---->  2 H2O

 
Writing Formulas:  Applying the Main Ideas

    The drawings below show molecules of various compounds.  Under each drawing, write the correct formula for the compounds

 
 
 
 
 

Part C Balancing Equations

    Chemical changes are characterized by the formation of new substances.  The product of a correctly balanced chemical equation represents the number and kind of new substance formed.  There are three main types:  Synthesis, Decomposition, Replacement.  Replacement is further broken down into single and double replacement.  Identify each equations as one of the 3 main types.

    Examine each equation listed below and determine if the equation is in need of balancing.  Then balance the equation.  Remember to use coefficients, not subscripts, to balance the equation.

        1.  ___ Na  +  ___ O₂ --->  _____Na₂O
 

        2.  ___H₂   + ____ O₂ ----->___H₂O
 

        3  ___Na₂SO₄  + ___CaCl₂ ---> ___CaSO₄  + ____NaCl
 

        4.  Al₂O₃ --->  _____Al + _____O₂
 

        5.  ___ N₂  + ____H₂  --->NH₃
 

        6.  ____Fe  +  ____H₂O  ---> ___Fe₃O₄ +  ___ H₂
 

        7.  ___ P₄   +  ____O₂ ---> ___P₄O₁₀
 

        8.  ___C₂H₆  +  O₂ --->  ___  CO₂  + ____ H₂O
 

        9.  SiCl₄ --->   ___Si  +  ___Cl₂
 

        10.  ___ C  +  ___H₂  --->   ___CH₄