1. Understanding Chemical Formulas and Substance Compositions
The Structure of Matter
Structure and Properties of Matter
Combining Atoms
Activity
Many, many substances encountered in daily life will not be found on the Periodic Table of Elements. Most substances consist of combinations of atoms called molecules. Molecules can have as few as two atoms or can contain thousands of atoms. Molecules are described using chemical formulas which define what type and how many atoms are present. The small numbers which follow some element symbols are called subscripts, and they tell us how many atoms of that element are present in the molecule. For example, the formula for water, H2O, indicates that the water molecule is made up of two hydrogen atoms and one oxygen atom.
Procedure
Use the Periodic Table and analyze the chemical formula to construct a model of each molecule using the Molecular Model kits.
Fill in the number and type of each atom in the molecule in the substance composition column.
Fill in the boxes provided with the color noted in the KEY to represent the model.
Do Task 2
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SR-Copy editing addressed, 6/2
Understanding Chemical Formulas and Substance Compositions
Chemical formula
Name of substance
Substance composition:
Number and type of each atom in a molecule of the substance
Drawing of model using KEY
oxygen O = red
Hydrogen H = black
carbon C = yellow
Nitrogen N = blue
Sodium Na = green H2
Hydrogen gas O2
Oxygen gas O3
Ozone
H2O
Water
CH4
Methane
NaOH
Sodium hydroxide
N2O
Nitrous oxide
H2CO3
Carbonic acid 1

2. Combining Atoms Activity, continued Join in a class discussion.
The Structure of Matter
Structure and Properties of Matter
Combining Atoms
Activity, continued
Join in a class discussion.
Write a statement that explains the meaning of a subscript in a chemical formula.
Put the molecule models of hydrogen gas, oxygen gas, water, and sodium hydroxide into the corresponding labeled cups.
Construct models for two molecules of hydrogen gas and two molecules of oxygen gas and place all four molecules in the fifth cup.
Whole class:
Each group empty cup 1 into bowl 1
Repeat for each cup 2, 3, 4, and 5.
Describe the contents of each bowl. Use this information to write an evidence supported statement to conclude if the substance in each cup is a pure substance.
10. Remove the hydrogen molecules from the 5 bowl, then construct and add two molecules of ozone to the oxygen molecules in the cup.
Describe the contents of the cup. Use this information to write an evidence supported statement to conclude if the substance in each cup is a pure substance. 2