Atomic Spectroscopy Laboratory

Science & Engineering Magnet High

Mr. Puckett

Atomic Emission Spectroscopy Laboratory

• Problem: How much energy is contained in the quanta between the different levels of excited electron energy orbitals? And what are the frequencies and wavelengths of the energy?

• Hypothesis: The amount of energy given off is calculated by the colors of the quanta of light given off when the electrons “cascade” from upper energy levels to the natural ground state.

Introduction and theory• Atomic Spectroscopy is the analytical

measurement of the quantum energy level jumps of different electron energy states.

• It is a spectral analysis of the colors (frequencies or wavelengths) that an atom gives off when it changes energy levels.

• Formulas: c = f and 1/ = R(1/nf2 –1/ni

2) where R = 1.097 x107 m-1 and n is the orbital of the energy state.

• The shortcut formula is E = Ef – Ei = E2 – E1 where E = -13.6 eV / n2 , then E = hf.

Atomic Emission Spectroscopy

• In this technique, the atoms are heated up to the point that the thermal energy promotes the electron up to an excited energy level and then measures the color (wavelength) of light that is given off when the electron collapses back into the ground state. You are looking into the atom

Einstein proposes Quanta Energy Levels of Electrons

• Einstein also proposed that electrons, besides emitting electromagnetic radiation in quanta, also absorb it in quanta.

• Einstein's work demonstrated that electromagnetic radiation has the characteristics of both a wave--because the fields of which it is composed rise and fall in strength--and a particle--because the energy is contained in separate "packets." These packets were later called PHOTONS.

Energy Orbitals of the Electrons

• Electron energy orbitals are the regions where there is the greatest chance to find them as clouds

Photon Energy Emitted out of the Excited Level Electrons

• When the electron absorbs the energy, it is promoted to the higher energy orbital.

• Nature wants the electron to go back to the ground state level (stability and entropy reasons) and give the energy back off at frequencies that are unique for that atom at that level of energy.

Materials and Procedures

• Materials:– 1. A hand held spectrometer.– 2. A Fluorescence gas element tube with

Hydrogen.

• Procedures:– 1. Turn the tube on to glow with lights reduced– 2. View the light through the spectrometer– 3. Record the emission lines as 102 nm.

Emission Spectroscopy Examples

Energy Level Transitions of Electrons

Energy Levels Chart Example

• Notice the many different pathways photon energy release can take back to ground state.

Results:

• The results are a combination of measured visual colored spectral lines and the calculated energy levels for the electrons.

Orbital Energy for the Atomic Hydrogen Spectroscopy

Frequency and Wavelength of Emitted Photons

Error Analysis:

• The main source of error in this experiment is the angle of the spectrometer in relation to the light tube. This angle can produce numerical results that vary as much as 100 nm. Over a hydrogen spectrum at 410 nm this would be 100/410 x 100% = 24.4 % error down to 16% at 656nm.

• To correct the error a computerized spectrometer could be used to obtain more accuracy.

What YOU Learned in this lab

• Students will supply the answer to this.

• Should be at least half a page and be a synopsis of the experimental theory and results with quantification.