Line Spectrum Observation

observing emission spectra

I. continuous spectrum

Continuous spectra of light are formed by all forms of white light. This includes light produced by common light bulbs like incandescent and fluorescents. The incandescent light actually contains 7 colors of light: Red, orange, yellow, green, cyan, blue, and purple. And from red to purple the wavelength decrease respectively. A continuous spectrum is produced by exciting atoms with electricity or radiation and the atoms of different elements give off radiation specific to the element. If all elements are present a continuous spectrum will be produced otherwise a bright line spectrum will be produced by the elements present. so we can let incandescent light to be reflected in the prism and then the rainbow-like continuous spectrum with all those visible light from the spectroscope will be displayed.

II. Line Spectrum and the Spectrum of Hydrogen atom

A non-continuous spectrum occurs when an electric current passes through a gaseous element in a gas discharge tube or when metal ions are put into a flame. This type of spectrum, called a bright line spectrum, is not continuous but instead contains only certain colors at particular wavelengths. A bright line spectrum is due to transitions of electrons between energy levels in atoms or ions. When an atom or ion absorbs energy, such as from a flame or electrical source, it absorbs only certain discrete amounts of energy. These amounts are the difference in energy between lower and higher electron energy levels. When the electrons return to lower energy levels, energy is emitted in the form of a photon. Since atoms have a number of energy levels available, there are a number of different energies that can be absorbed and released.

in this experiment, the incandescent light passed through a prism or diffraction rough, and it split into various colors.

The emission spectrum of atomic hydrogen is divided into a number of spectral series and these observed spectral lines are due to the electron making transitions between two energy levels in the atom.

III. emission spectrum & Convergence

The emission spectrum of a chemical element or chemical compound is the spectrum of frequencies of electromagnetic radiation emitted due to an atom or molecule making a transition from a high energy state to a lower energy state. The photon energy of the emitted photon is equal to the energy difference between the two states.

When the electrons in the atom are excited, for example by being heated, the additional energy pushes the electrons to higher energy orbitals. When the electrons fall back down and leave the excited state, energy is re-emitted in the form of a photon. The wavelength (or equivalently, frequency) of the photon is determined by the difference in energy between the two states. These emitted photons form the element's spectrum.

The fact that only certain colors appear in an element's atomic emission spectrum means that only certain frequencies of light are emitted. Each of these frequencies are related to energy by the formula:

Because of the equation E=hv=hc/λ, the larger energy is, the longer wavelength is. That means, when the electrons “jump” to the same energy level, if the wavelength become shorter, the energy difference between two electronic transitions become smaller. The lower electron energy transitions n=1 to n=2 or 2 to 3 or 3 to 4 etc. are smaller in energy than say, 5 to 6 or 7 to 8, and lower energy transitions correspond to lower energy photons which equals shorter wavelengths. So the first few transitions might be very close in energy, meaning their emitted photons will "converge" while the higher energy transitions will have a much larger energy difference and therefore more spread out in the spectrum.

IV. observation of The Atomic Spectrum of Hydrogen

Hydrogen(H): Pink

Red, cyan and purple lines were presented clearly. Yellow line wasn’t very clear but still could be observed. The lines were not very dense and the distance between cyan and purple lines was relatively small than others. The converge phenomenon appeared

Helium (He): Yellow

There were eight clear, separated lines (two of them were a little bit dark).

Mercury (Hg): Light blue

Red, orange, green, purple lines were presented by the spectroscope. Red line was the darkest one and the green one was the brightest one.

Argon (Ar): Pink

Many lines in different colors were presented. The purple line was relatively brighter than other lines.

Nitrogen: Red pink

Many lines in different colors were presented. Red lines on the left was not very clear.

IV. observation of flame test

Only metals, with their loosely held electrons, are excited