1. Putting atoms together
Interpreting Formulas
Putting atoms together

2. Molecules
Most substances are not made up of individual atoms. Instead, they are made up of molecules.
A molecule is a group of atoms that are chemically joined.
Ex. oxygen, carbon dioxide, water vapour

3. Molecular Elements An oxygen atom: O Oxygen molecules: O2 and O3
oxygen gas ozone
There are 7 elements that form molecules consisting of two atoms:
H2,O2, F2, Br2, I2, N2, Cl2

6. Compounds (very similar to molecules)
A pure substance that contains two or more elements
Ex. CO2, N2O3, NaCl

7. Interpreting Formulas
A chemical formula tells you important information about a pure substance:
The symbols tell you the elements in the substance
If there is only one symbol, the substance is an element
If there is more than one symbol, the substance is a compound
The subscripts tell you how many atoms of each element are in each molecule of the substance

8. Ex. Interpret the chemical formula for sodium carbonate (Na2 CO3)
How many elements are in the formula?
How many atoms of each element are in the formula?
What is the total number of atoms in the chemical formula?

9. Ex. Interpret the chemical formula for sodium carbonate (Na2 CO3)
1. How many elements are in the formula?
Sodium, carbon, and oxygen
2. How many atoms of each element are in the formula?
Na = 2 C = 1 O = 3
3. What is the total number of atoms in the chemical formula?
There are 6 atoms in the formula for Na2CO3
Practice: Interpret the formulas of these compounds:
Butane (C4H10)
Sulfuric acid (H2SO4)

10. Classwork
pg.251 #1, 2, 3, 5, 7