Overview
This lecture demonstrates atomic spectra using a diffraction grating to compare the continuous spectrum of an incandescent bulb and the emission spectra of mercury, nitrogen, neon, and hydrogen.
Continuous and Atomic Spectra
- An incandescent bulb emits a continuous spectrum, showing all visible wavelengths (violet to red).
- Elements (mercury, nitrogen, neon, hydrogen) emit discrete spectra, with specific colored lines unique to each element.
- A diffraction grating separates light into its component wavelengths, similar to a prism.
Diffraction Grating
- A diffraction grating is a clear plastic etched with 10,000–13,000 lines per inch, used to resolve light into spectra.
- When light passes through the grating, its spectrum appears as distinct images with colors spread right and left from the central source.
Element Spectra Demonstrations
- Mercury: Emits bright green and blue spectral lines; common in street lights.
- Nitrogen: Shows a spectrum with red, orange, yellow, green, violet, and turquoise lines.
- Neon: Produces many red and orange lines; basis for traditional neon lights.
- Hydrogen: Shows three main lines (red—hydrogen alpha, turquoise—hydrogen beta, and violet—hydrogen gamma).
Hydrogen Spectrum and Applications
- The three visible hydrogen lines come from electron transitions to the second energy level (Balmer series).
- The hydrogen alpha (red) line is important in astronomy for identifying nebulae and stars.
Key Terms & Definitions
- Continuous Spectrum — A spectrum showing all visible colors without gaps (e.g., incandescent bulb).
- Emission Spectrum — Spectrum consisting of bright lines from specific wavelengths emitted by elements.
- Diffraction Grating — An optical device with fine lines for separating light into spectra.
- Balmer Series — Visible lines in the hydrogen spectrum from electron transitions to the second energy level.
- Hydrogen Alpha Line — Red spectral line in the hydrogen emission spectrum.
Action Items / Next Steps
- Review the hydrogen spectrum and relationship to electron transitions (Balmer series).
- Prepare for laboratory experiments involving identification of elements using emission spectra.