Christmas Chemistry

The Chemistry of Christmas - Sights, Smells, and Feelings

Behind all the beauty of the holiday season, chemistry is there at work.  The lights we see involve a chemical process.  Particular chemical compounds are present in the items with pleasant smells, such as the fragrance of a spruce tree.  Even the joyful feelings we experience during visits with family and friends, along with the exchange of gifts, occur because of a change in our brain chemistry itself.

The Focus of This Posting

This post is a focus on the chemistry of light (Light Emitting Diode (LED) ) and aromatic compound smells (aka essence of pine) as we experience the joys of the holiday season.  Each process indicated above involve light-matter interactions and olfactory nerve biochemistry.

The LED and Pine Aroma

LED's are becoming more popular because of their high efficiency and long life.  Within the LED are two semiconducting plates  separated by just the right distance to produce visible light.  One plate is missing electrons (has positively charged "holes") and the other plate has excess electrons (negative charge).  The positive plate is at a lower potential energy level than the negative plate.  When a sufficient current is applied to the diode high energy electrons fly across the gap and are embedded in low energy "holes".  In the process, electrons lose energy which is than emitted in the form of light.

 

The pleasant odor of pine involves a class of compounds known as Terpenes.  When terpene molecules encounter nasal olfactory nerves, they are absorbed by similarly-shaped receptors in what is known as a "lock and key fit".  The presence of the terpene molecules induces a complex series of biochemical changes within the olfactory membrane resulting in an electrical signal sent to the brain.  Then we sense the wonderful aroma of pine!

 

The following diagram illustrates the two processes.

 

Here's wishing you and yours a very Merry Christmas and a Happy New Year!

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