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 Valerie Posted 2.24 SR-no corrections per science review, 6/2 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

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