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Atomic Line Spectrum

Matter emits light at various wavelength. Excitation of certain elements or the electrical excitation of certain elements give rise to an atomic line spectrum unique to that atom.

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Hydrogen Atom and Line Spectrum

Hydrogen Line Spectrum
When hydrogen gas (or other element) receive high energy spark it emits light with specific λ-wavelength signature
H₂ (g) absorb energy (H-H bond breaks) H atoms

 

 

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Bohr Planetary Model of the H-atom

Bohr Atomic model of the Hydrogen atom
• Electrons follows circular orbits around the nucleus
• Electrons could have only certain size orbits (quantum condition)
• electrons are allowed to higher orbit with an input in energy.

Bohr Model of the H-atom

What is the origin of the Atomic Line spectrum ?

The line emission line spectrum results from electrons dropping from higher energy level to lower energy levels. Each time an electron drops, a proton of light is released whose energy correspond to the difference in energy between the two levels.

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Atomic Line Spectrum H-atom

Transition of the electron from a high energy level to a lower energy level results in a photon emission which has a frequency related to the energy difference between the transition. The Rydberg equation is an empirical formula that can be used to predict the frequency, wavelength, or energy of the photon emitted upon electron relaxation. Johann Balmer Johannes Rydberg

Emission Lines for various atom is the EMR emission as a result of the electron relaxation from a higher orbital to a lower one. The Rydberg equation only works for the Hydrogen and Hydrogen-like (species with only one electron) however because Bohr model of the atom breaks down when there are more than two electrons. A more sophisticated theory of the atom was needed in order to determine the energy due to electron-electron repulsion. Consequently, the Schrodinger equation provide a mathematical model of the atom: H= E.

Line emission spectra for various elements. Excited gaseous elements produce characteristic spectra that can be used to identify the elements as well as to determine how much elements is present in a sample. Link: 1. David Whizzy's Periodic Table: Atomic Line spectrum for first 36 elements in the perioodic table

 

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Relative Energies for Shells and Orbital

The solution to the Schrodinger Equation lead to Quantum numbers which provide the address of the electrons in an atom. The following is a model of the atom based on this theory.

Erwin Schrödinger (1887 - 1961) was the only son of well-educated parents. His father owned an oil cloth factory and was an amateur painter and botanist. Erwin was taught at home, by tutors and parents, until he was 11. He then attended school to prepare for university. Schrödinger began to think about explaining the movement of an electron in an atom as a wave. By 1926 he published his work, providing a theoretical basis for the atomic model that Niels Bohr had proposed based on laboratory evidence. The equation at the heart of his publication became known as Schrödinger's wave equation. This was the second theoretical explanation of electrons in an atom, following Werner Heisenberg's matrix mechanics. Many scientists preferred Schrödinger's theory since it could be visualized, while Heisenberg's was strictly mathematical. A split threatened among physicists, but Schrödinger soon showed that the two theories were identical, only expressed differently.

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Summary

Light travel through space as a wave of radiation energy. The crest-to-crest distance between waves is the wavelength, and the number of cycles completed in a second is the frequency.

In 1900 Max Planck introduced the quantum concept. When an object radiates light, it releases a unit of radiation energy called a photon.

In 1913 Niels Bohr suggested that electrons travel in curricular orbits about the nucleus. The electron possesses a specific energy and it is said to occupy an energy level. If an electron changes orbital in the Bohr model, there is a quantum energy change. The line emission line spectrum results from electrons dropping from higher energy level to lower energy levels. Each time an electron drops, a proton of light is released whose energy correspond to the difference in energy between the two levels.

In the 1920's our understanding of electrons in atoms became very sophisticated. It was proposed that the energy of electrons can be known only in terms of its probability of being located some where within the atom. The description gave rise to the Quantum mechanical atom. A location within the atom where there is a high probability of finding an electron having certain energy is called an orbital.