Direct observation is something that we can perform everyday.   If you see an object like a car, you do not have to do any further investigation.  You can touch and see it directly and you can identify it without a doubt.  When you wake up in the morning there might be the smell of coffee brewing.  You do not have to actually see it but your sense of smell confirms the product.    However, you would still have to confirm by actually seeing or tasting the coffee. 

Birds may be chirping outside and you know there are birds by the sound.  Do you have to confirm by seeing them to know they are there?   Yes, because it could be an audio recording, the television, or person that can imitate birds. Confirmation is needed to be absolutely sure.   

What happens if you cannot see, touch, feel, or smell?  Can you still determine what it is?  This is the case of ions and molecules because you cannot directly see anything that small.    We can indirectly see them through x-rays, particle accelerators, and some very high powered microscopes.  How

the atoms actually look like and how the electrons move is still very “cloudy.”  So chemists and physicists develop models to try and show the evidence they are see.   In the Unit on “Atomic Theory” we will look at the historical development of how we think an atom actually works.

Models help humans to think about how the actual might look like if our eyes could see substances that small.  Analogical models helps explain objects and processes that we cannot readily observe.  Hypothetical models help us try to visualize how something works even if we cannot see it.