Lecture Notes: Formation of Spectral Lines

Introduction

• Discussion on formation of emission and absorption lines.
• Reference to Bohr’s model of the atom.

Excitation and De-excitation

• Excitation: A packet of light (photon) with the right energy can boost an electron to a higher energy state.
• De-excitation: Electrons cascade back to a lower energy state, emitting a photon of the same energy.

Energy States in Atoms

• Historically, Bohr’s model suggested energy states were spaced equally.
• Today, it’s understood there are infinite energy states that get closer as they increase.
• Ionization: When an electron is ejected from an atom, passing the threshold energy.

Emission and Absorption Lines

• Absorption Line: Occurs when an atom absorbs energy, elevating an electron to a higher state.
• Emission Line: Happens when an electron drops to a lower energy state, emitting energy as a photon.

Methods of Excitation

• Dense Environments: Atoms can excite through collisions (e.g., in gases or liquids at room temperature).
• Low-Density Regions: Excitation occurs when specific photons are absorbed.

Spectra and Atomic Structure

• Different atoms have unique spectra due to their unique energy level structures.
• Multiple electron atoms (e.g., Helium, Carbon) have more complex spectra with many lines.

Hydrogen Atom and Balmer Series

• Hydrogen: Consists of a single proton and electron, making it simpler to study.
• Balmer Series: Visible light spectral lines from hydrogen.
  • Hydrogen-alpha: Electron cascades from level three to level two.
  • Hydrogen-beta: From third excited state down to first.
• Lyman Series: Involves transitions from the ground state to higher levels, leading to ultraviolet light emissions.

Important Terms

• Excitation: Moving an electron to a higher energy level.
• De-excitation: Electron descends to lower energy levels, releasing energy.
• Ionization: Electron is removed from an atom.
• Ionization Energy: Energy needed to remove an electron from an atom.

Kirchoff's Laws and Absorption Spectrum

• Absorption Spectrum: Occurs when cooler gas absorbs specific photons from a hot source, causing electron excitation.

Complexity in Atoms

• More electrons mean more complex interactions and spectra.
• Larger atoms (e.g., Carbon) have more possible electronic changes and spectral lines.

Conclusion

• Hydrogen’s simplicity makes it vital for study, but other elements offer more complex spectra.
• Understanding spectral lines helps identify elements and their behavior in various environments.