Overview
This lecture demonstrates atomic spectra using a diffraction grating to compare the continuous spectrum of an incandescent bulb and the emission spectra of four elements: mercury, nitrogen, neon, and hydrogen.
Introduction to Atomic Spectra
- Atomic spectra show the light emitted or absorbed by elements as distinct patterns.
- A diffraction grating is used to separate light into its component wavelengths, similar to a prism.
Continuous vs. Discrete Spectra
- Incandescent bulbs emit a continuous spectrum with all visible wavelengths from violet to red.
- Elemental gases in discharge tubes emit discrete (line) spectra unique to each element.
Diffraction Grating
- A diffraction grating has 10,000–13,000 lines per inch and separates light into its spectrum.
- When placed in front of a light source, it shows distinct spectral lines or bands.
Element Spectra Demonstrations
Mercury
- Mercury spectrum is mostly blue and green lines.
- Mercury vapor lights are commonly used as street lights due to their bluish tint.
Nitrogen
- Nitrogen spectrum contains multiple colored lines: red, orange, yellow, green, turquoise, and violet.
Neon
- Neon emits many red and orange lines, resulting in the bright orange-red glow of neon signs.
- Neon was the original gas used for neon lights, though other gases are now also used.
Hydrogen
- Hydrogen shows three main lines: red (hydrogen alpha), turquoise/greenish-blue (hydrogen beta), and violet (hydrogen gamma).
- These lines are part of the Balmer series, corresponding to electron transitions ending at the second energy level.
Key Terms & Definitions
- Atomic Spectrum — The set of wavelengths of light emitted or absorbed by an element.
- Continuous Spectrum — Unbroken range of colors (wavelengths) emitted by sources like incandescent bulbs.
- Emission Spectrum — Distinct lines of color emitted by excited atoms of an element.
- Diffraction Grating — An optical device with closely spaced lines used to separate light into spectra.
- Balmer Series — Specific spectral lines of hydrogen due to electron transitions to the second energy level.
Action Items / Next Steps
- Review the Balmer series and electron transitions in hydrogen.
- Prepare for upcoming labs involving hydrogen spectral lines.
- Observe and note differences between continuous and emission spectra in class or lab.