Flame Tests and Spectroscopy: Get Excited About Color

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Have you ever wondered what makes fireworks sparkle with color, why decorative fireplace logs burn green or blue, or how birthday cake candles burn with a flame that matches the candle? Students can investigate the phenomenon of colored flames using flame tests and spectroscopy.

This visually impactful lab incorporates quantitative data to help explain abstract aspects of atomic theory and electron behavior. What happens as electrons gain additional kinetic energy from a heat source? How does electron energy relate to color? Find the explanation below.  

Bohr’s Atomic Model

Bohr's atomic model

 In the Bohr model of the atom, electrons are arranged in circular pathways around the nucleus, which are dictated by a fixed amount of energy corresponding to its pathway. The electrons can move, or jump, from one level to the next by absorbing or emitting a given amount of fixed energy termed a quantum of energy.

 

 

Quantum theory holds that electrons around a nucleus are located in discrete energy levels. When energy is supplied to an atom through light or heating a substance, the electrons absorb part of the energy and jump from a low-energy or ground state to a higher energy level or excited state. Consider a single electron. After absorbing energy, it moves faster and farther from the nucleus. The electron is in an excited state. However, the excited state is not stable, and thus the electron ultimately returns to its original, lower-energy ground state.

The electron falls back to its lower-energy or ground state, once previously absorbed energy is released. The energy emitted is a photon of light of specific wavelength or color. A flame test exposes electrons to heat, resulting in signature colors of flame , enabling identification of elements.

Because different atoms have unique electron orbital arrangements, they emit unique and identifiable spectral line patterns. The human eye sees the combined result of the electron energy changes as one color. You may be asking yourself how can a color such as red be limited to one element?

Through a Spectroscope

Scientists developed a tool to break down the color into its spectral line components. A spectroscope splits the emitted light into its component wavelengths when the light passes through a diffraction grating. In a flame test, all the wavelengths of light emitted by an element’s electrons blend into a particular color perceived by the human eye. When the colored flame is viewed through a spectroscope, the diffraction grating splits the incoming light into the component wavelengths, so that identification and measurement of the element’s unique color bands, or spectrum, is possible.

Highly abstract concepts of atomic structure and electron behavior become visible in an engaging display of color and light. Use the Like Salt to a Flame lab kit and the infographic Flame Test Colors and Bright-Line Emission Spectra for Metal Chlorides to facilitate lab setup, procedures, and data analysis. Be the teacher to ignite flames of wonder and passion for science in your students!

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