The Interaction of Light and Matter

#Emission Line Spectra and Electron #Transitions

Greetings,

Forms of Electromagnetic Energy - Matter #Interaction

This post is a focus on electromagnetic (e.g. light) energy and its interaction with atoms.  This is the last post before we begin discussions on chemical bonding.  Many different "forms" (ie frequencies) of electromagnetic energy #interactions with matter exist; atomic electron transitions, molecular electron transitions, chemical bond vibrational-energy absorbance, proton-spin radio-wave absorbance, microwave-energy effects on molecular rotation, and x-ray solid-matter deflections.  We'll focus on atomic electron transitions which involves visible light energy.

Examples of Atomic Emission

There is evidence of light-energy atomic interactions every time we switch on a fluorescent light or visit an establishment with "neon" lights.  "Neon" lights contain other Noble Gases, such as xenon, argon, and helium, as well.  Fluorescent lights work via a promotion of electrons to higher energy levels (using an electrical discharge) followed by a rapid return of those electrons to lower energy states and emission of visible light.

#Line Spectra Explained

Individual atoms of different elements absorb (and emit) various patterns of individual light energies which chemists utilize to identify and quantify elements contained in samples of matter.  These light energy transitions are called line spectra because they literally show lines of energy absorbed and emitted.  The Bohr Model of the Atom was able to accurately predict the line spectra of hydrogen, therefore a direct connection between Bohr energy-level transitions and hydrogen's line spectra (absorbance and emission) can be made.  The video below shows the connection between the hydrogen emission line spectrum and Bohr diagram electron transitions. 

Hydrogen Line Emission Energies and Electron Transitions

If you've watched the presentation, you would have noticed that the electrons start at higher energy levels.  This higher-energy electron condition is not the "normal" state of hydrogen atoms; in fact, in the absence of focused energies with the required wavelengths (at each spectrum line), hydrogen atoms are at their lowest energy level (ground-state) and the electron is found in Bohr shell no. 1.  The "starting" positions of electrons just before light is emitted (the excited state) are reached by the absorbance of light energies at the line wavelengths. The "nm" unit is the wavelength of visible light in #nanometers: There are 1,000,000,000 nm to 1 m (meter).  The following figure shows how wavelength is determined.  The symbol for wavelength is the Greek letter lambda.

That's all for now.   My next post will begin the very important topic of chemical bonding.

Have a good one!