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I am teaching my chemistry students about electron transitions in an atom by absorbing or emitting a photon of light. Are there other mechanisms for exciting an electron that do not involve a photon?

My particular question has to do with the burning of metal salts to produce a characteristic spectra. It is clear from the line spectra that we are seeing a quantum effect of the electrons transitioning between levels. What is the mechanism for the electron excitation?

Question Date: 2010-03-21
Answer 1:

Your lesson plan sounds really interesting! As you mentioned, light is emitted when an excited electron transitions energy levels back to its ground state. One way to excite an electron, like you said, is by absorbing photons of light. Glow in the dark toys are an example of this- you have to hold them up to a light to charge them, and they are made of special phosphorescent materials in which the electrons fall back to the ground state slowly so that the glow is sustained. Light is not the only way to excite an electron. Thermal energy can also raise the electron to a higher energy state, which is what is happening in your metal salt burning experiment. The cause of excitation is the heat, and light is emitted when the electron returns to the ground state. Each metal salt has a characteristic light color that it releases. Metal salts can be incorporated into fireworks to give them color. In addition to light and heat, another way that electrons can get excited is through the direct transfer of energy that occurs when the electron collides with another atom or electron.I hope this answers your question, please feel free to contact me if you have more.

Answer 2:

There are a number of ways in which atoms can be brought to an excited state. Photoexcitation, happen when an electron absorbs a photon and gains the photon's energy. Electrons can also be excited by electrical excitation, where the original electron absorbs the energy of another, energetic electron. The simplest method is to heat the sample to a high temperature. The thermal energy produces collisions between the sample atoms causing the atom's electrons to be excited.

When an excited electron falls back to a lower energy state again, it is called electron relaxation. The resulting emission spectrum can be used to determine the composition of a material, since it is different for each element of the periodic table.

One example is astronomical spectroscopy:
identifying the composition of stars by analysing the received light. The emission spectrum characteristics of some elements are plainly visible to the naked eye when these elements are heated. For example, when platinum wire is dipped into a strontium nitrate solution and then inserted into a flame, the strontium atoms emit a red color. Similarly, when copper is inserted into a flame, the flame becomes green.

These definite characteristics allow elements to be identified by their atomic emission spectrum. Not all lights emitted by the spectrum are viewable to the naked eye, it also includes ultra violet rays and infra red lighting, an emission is formed when an excited gas is viewed directly though a spectroscope.

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