Are some molecules small

Pour a small amount of vanilla extract into the balloon. Blow up the balloon. Do not get any vanilla extract in your mouth. Tie off the balloon. Shake the balloon for about thirty seconds. 

Smell the outside of the balloon. Do you smell the vanilla extract How does it get on the outside of the balloon  

Vanillin molecules are found in vanilla extract. Vanillin is a molecule made of eight carbon atoms, eight hydrogen atoms, and three 

The outside of the balloon smells like vanilla extract because the vanillin molecules pass through the walls of the balloon even though it is closed. There is enough space between the molecules in the balloon to let the vanillin molecules pass through the balloon. Like many molecules vanillin molecules are very small. 

Try other smelly things like almond extract or lemon extract to see if they can get out of the balloon. 

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