Radiation and Thermal Energy

Our Model of the Atom Evolves

• In a chemical reaction, what is happening to the system when there is a change in temperature?

• What changes occur in a system when radiating is the transfer mechanism?

Observations?

Incandescent light bulb

• Watch carefully as the power delivered to the light bulb is increased.

• Write down your observations.

Incandescent light bulb

• Now view the light bulb through a spectrometer as the power delivered to the bulb is increased.

• Write down your observations

Compact fluorescent light bulb

• Watch carefully as the power delivered to the light bulb is increased.

• Write down your observations.

Compact fluorescent light bulb

• Now view the light bulb through a spectrometer.

• Write down your observations

What is the difference?

• A hot solid gives a continuous spectrum while a heated gas gives only a piece of the spectrum.

• An input of energy is required to make the atoms of an atomic gas emit radiation.

• The radiation emitted by each element is unique.

• A change in temperature results in a change in structure.

• A change in structure results in the emission of light.

• In a compound a change in structure can be explained by a rearrangement of the atoms.

• How about in atomic gases?

• In atomic gases the change in structure has to be at the atomic level.

Our current model of the atom….

• Does not account for these differences in structure, therefore we need a model of the atom with some more internal structure that can account for the radiation emitted by atoms.