1. Molecules, Atoms and Compounds

2. A substance made up of only one kind of atom.
Element
A substance made up of only one kind of atom.
Examples: Helium, Copper, and Gold

3. A substance made up of 2 or more DIFFERENT elements.
Compound
A substance made up of 2 or more DIFFERENT elements.
Examples: Copper II oxide, salt (NaCl) and water (H2O)

4. Element or Compound? Ca
Na2O O2

5. Can be written with Chemical Symbols
1 or 2 letters used to represent an element
1st letter is always capitalized
If there is a 2nd letter it is lower case

6. Subscripts indicate the number of atoms of the element.
Chemical Formulas
Subscripts indicate the number of atoms of the element.
Example: AlCl3
1 aluminum atom
3 chlorine atoms

7. Chemical formulas
Practice:
NH4Cl
Mg(OH)2
Pb(NO3)2

8. Drawing Molecules
represents a molecule made up of 2 different elements
Another way to draw a molecule:

9. Draw a pictorial representation of the following:
Drawing Molecules
Draw a pictorial representation of the following:
Oxygen
Calcium Ca O2
CaO

10. Drawing Practice
H2O
NH3
CCl4