3. Atoms : Building Blocks of Matter The formula for a compound indicates the elements that make up the compound and the number of atoms of each element present in that specific compound. These numbers of atoms are indicated by the use of small numbers called subscripts . Sometimes groups of atoms act as a group of atoms. Such a group of atoms is called a polyatomic ion.

4. Atoms : Building Blocks of Matter When a subscript appears outside the parentheses , it indicates that all the elements inside the parentheses should be multiplied by that subscript. Fe(OH) 3

7. Counting Atoms Trinitrotoluene = (TNT) explosive C 7 H 5 (NO 2 ) 3 C= Carbon = 7 H = Hydrogen = 5 N = Nitrogen = 3 O = Oxygen = 6

8. Counting Atoms As you look over these compounds you may observe that many of them contain similar _________ of elements. Since we are a ______________ based environment, carbon is found in all living organisms. The elements in the Human Body can be broken down to include the main elements of Hydrogen, Oxygen, Nitrogen, Carbon and representatives from about 20 other elements. atoms carbon

9. Counting Atoms The _ ____ ____ main elements that make up most living organisms are Carbon, ________________, Sulfur, __________________, Oxygen and _____________. Phosphorus SIX Hydrogen Nitrogen