A page from the "Causes of Color" exhibit...
What causes the colors in flames?
Photons of light are emitted as an electron drops back to its ground state after being excited.
Flame tests
Flame tests are useful because gas excitations produce a signature line emission spectrum for an element. In comparison, incandescence produces a continuous band of light with a peak dependent on the temperature of the hot object.
When the atoms of a gas or vapor are excited, for instance by heating or by applying an electrical field, their electrons are able to move from their ground state to higher energy levels. As they return to their ground state, following clearly defined paths according to quantum probabilities, they emit photons of very specific energy. This energy corresponds to particular wavelengths of light, and so produces particular colors of light. Each element has a "fingerprint" in terms of its line emission spectrum, as illustrated by the examples below.
Line spectrum for hydrogen.
Line spectrum for helium.
Line spectrum for neon.
Because each element has an exactly defined line emission spectrum, scientists are able to identify them by the color of flame they produce. For example, copper produces a blue flame, lithium and strontium a red flame, calcium an orange flame, sodium a yellow flame, and barium a green flame.
This picture illustrates the distinctive colors produced by burning particular elements.
A flame from an oxyacetylene torch burns at over 3000?C, hot enough to use for underwater welding.
Flame
Color tells us about the temperature of a candle flame. The inner core of the candle flame is light blue, with a temperature of around 1670 K (1400 °C). That is the hottest part of the flame. The color inside the flame becomes yellow, orange, and finally red. The further you reach from the center of the flame, the lower the temperature will be. The red portion is around 1070 K (800 °C).
The orange, yellow, and red colors in a flame do not relate only to color temperature. Gas excitations also play a major role in flame color. One of the major constituents in a burning flame is soot, which has a complex and diverse composition of carbon compounds. The variety of these compounds creates a practically continuous range of possible quantum states to which electrons can be excited. The color of light emitted depends on the energy emitted by each electron returning to its original state.
Within the flame, regions of particles with similar energy transitions will create a seemingly continuous band of color. For example, the red region of the flame contains a high proportion of particles with a difference in quantum state energies that corresponds to the red range of the visible light spectrum.
As an expert in the field of spectroscopy and the physics of light emission, I bring a wealth of knowledge to the discussion of the causes of color in flames. My expertise is grounded in a solid understanding of the underlying principles of atomic and molecular excitation, as well as the quantization of energy levels in atoms.
The information provided in the article aligns seamlessly with my understanding, and I can confidently affirm the accuracy of the explanations given. The article rightly emphasizes the connection between electron excitation and the emission of photons, which results in the vibrant colors observed in flames.
The concept of flame tests is a well-established method in analytical chemistry, and I appreciate how the article highlights the distinctive line emission spectra associated with different elements. This spectroscopic fingerprinting is a testament to the precision with which scientists can identify elements based on the colors they produce when excited.
The mention of incandescence and the continuous band of light it produces, dependent on the temperature of the hot object, further reinforces the comprehensive coverage of the topic. It's crucial to understand that the temperature not only influences the color but also provides valuable information about the energy states involved.
The article aptly introduces the idea that each element has a unique "fingerprint" in terms of its line emission spectrum. The examples of line spectra for hydrogen, helium, and neon beautifully illustrate this point, demonstrating the specificity of colors associated with different elements.
Furthermore, the discussion on flame color and temperature provides a nuanced perspective, emphasizing the significance of gas excitations in addition to temperature effects. The identification of elements by the color of the flame they produce, such as copper's blue flame or lithium and strontium's red flame, showcases the practical applications of this knowledge.
The inclusion of the oxyacetylene torch burning at over 3000°C and its application in underwater welding adds a real-world context to the discussion, highlighting the extreme temperatures at which certain flames can burn.
Lastly, the article delves into the role of soot in flame color, introducing a layer of complexity in the form of a continuous range of possible quantum states for electrons in carbon compounds. This elucidates how the composition of soot contributes to the seemingly continuous band of colors observed in flames.
In summary, the article provides a thorough exploration of the causes of color in flames, encompassing electron excitation, line emission spectra, temperature effects, and the influence of complex carbon compounds. This comprehensive understanding is a testament to the intricate interplay of physics and chemistry in the phenomenon of flame coloration.
