Question

An isolated atom can emit a photon, and the atom's internal energy drops. In fact, the process has a name: spontaneous emission. Can an isolated electron emit a photon? Why or why not?

Short answer

No, an isolated electron cannot emit a photon because it does not have multiple energy levels where it can either gain or lose energy.

Step-by-step solution

Understanding energy levels and photon emission

In normal circumstances, an atom or molecule absorbs energy to raise electrons to a higher energy level. When the electrons relax back into their original energy level, they emit the absorbed energy in the form of light, or photons. This is known as spontaneous emission.

Apply the understanding to an isolated electron

In contrast, an isolated electron does not have multiple energy levels. By itself, it's not in a state of being 'excited' to a higher energy state. The energy state of a lone electron is steady, and there is not any supernumerary energy to be expended.

Evaluate the possibility

Because there are no higher or lower energy states for the electron to move between, it does not have excess energy to lose. Hence, a lone electron cannot emit a photon spontaneously as a result of moving from one energy state to another - simply because distinct energy states do not exist for a single, solitary electron.

Key concepts

Photon Emission

Atoms can emit light known as photons. But this isn't just any light; it's specific in how it happens. Here’s the scoop.
When an atom absorbs energy, its electrons jump to higher energy levels. Imagine it as climbing a ladder. Now, these electrons don't stay up there forever. They like to relax back to their original spots.
When they do, they release energy—and this energy comes out as photons, or little packets of light.
Some important points about this process:

• This release of energy is called 'spontaneous emission'.
• It's spontaneous because the process happens naturally without force.
• The energy of the photon matches the energy difference between the two energy levels.

Every photon comes with a unique energy, and it depends on the electron's journey from one level to another.

Isolated Electron

Now, let's think about electrons out on their own. An isolated electron is like a person chilling in an open field—quite alone.
Unlike when electrons are in atoms, these free electrons don't have higher shelves, or energy levels, to climb up or down.
So what happens?

• An isolated electron stays stable. It doesn't naturally absorb extra energy.
• Without these extra energy levels, it can't release energy as a photon.

This means isolated electrons do not undergo spontaneous emission on their own. They need to be part of an atom with multiple energy layers to make this light magic happen.
Instead, they move freely unless acted on by outside forces.

Energy Levels

Energy levels are like stairs for electrons inside atoms.
Each step represents a different energy level, where higher steps mean more energy!
When an electron jumps from a lower step to a higher one, it absorbs energy.
Here’s what you need to know about energy levels:

• They are unique to each type of atom or molecule.
• Electrons can jump up or down between these levels.
• Jumping down emits photons, releasing light, while jumping up requires absorbing energy.

The difference between these levels decides the energy of the emitted photon during spontaneous emission.
So, energy levels are crucial for understanding how atoms emit light and how electrons behave when they're part of a complex structure, like an atom.