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# Electrons

## Defining characteristics of negatively charged subatomic particles and their role in atomic structure

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Practice Electrons

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How Exciting!

### How Exciting!

Credit: Jstuby
Source: http://commons.wikimedia.org/wiki/File:Lighningbug_trails.jpg

The faint trails of light in this field at dusk were produced by fireflies. Fireflies produce light to warn away predators or attract mates. Most people are intrigued by these glowing insects, but few know how they produce light. Do you know how?

#### The Back Story

• To understand how fireflies produce light, you first need to know about electrons in atoms. These tiny negative particles swarm around the positive nucleus of the atom at fixed distances from the nucleus, called energy levels.
• Credit: Dendroica cerulea
Source: http://www.flickr.com/photos/dendroica/5901727995/

Fireflies are actually winged beetles [Figure2]

• Electrons can be excited by absorbing energy. This causes them to jump to a higher energy level. This isn’t a stable situation, so the electrons quickly fall back down to their normal energy level. When they do, they give off the extra energy in the form of light.
• Excited electrons explain how fireflies produce light. If you’ve never seen fireflies in nature or just want to see their flashing lights again, watch this video:

#### Show What You Know

1. The scientist who first proposed that electrons are located only at certain fixed distances from the atomic nucleus was Niels Bohr. Outline Bohr’s atomic model and how it relates to the excitation of electrons.
2. In the third link above, the scientist gives an analogy for the excitation of electrons and how they give off energy when they return to their ground state. Describe this analogy.
3. Chemoluminescence is the general term for the method that fireflies use to produce light. Define chemoluminescence, and describe how it works.
4. When living things such as fireflies use chemoluminescence to produce light, the process is called bioluminescence. Describe the chemistry behind bioluminescence in fireflies.

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