Bohr Model - Flame Test, AES, Electron Configuration
This is part of preliminary HSC Chemistry course under the topic of Atomic Structure and Atomic Mass
HSC Chemistry Syllabus
- Model the atom's discrete energy levels, including electronic configuration and SPDF notation (ACSCH017, ACSCH018, ACSCH020, ACSCH021)
- Investigate energy levels in atoms and ions through:
- Collecting primary data from a flame test using different ionic solutions of metals (ACSCH019)
- Examining spectral evidence for the Bohr model and introducing the Schrödinger model
Bohr Model - Flame Test, AES, Electron Configuration
Flame Test
A simple approach to identifying a metal present in a ionic form within a sample is by conducting a flame test. In this process, a sample of the solution is introduced to the flame of a Bunsen burner. As the metal ions within the sample are heated, they emit light of a characteristic color unique to that specific metal ion. However, it's important to note that not all metal ions produce discernible colors when subjected to a flame test.
| Metal Ion | Flame Colour |
| Barium | Apple Green |
| Strontium | Scarlet |
| Lithium | Crimson |
| Sodium | Orange Yellow |
| Copper | Blue Green |
| Potassium | Lilac |
Atomic Emission Spectroscopy (AES)
Atomic Emission Spectroscopy (AES) is a method of chemical analysis that identifies elements within a sample by examining the intensity of light emitted from a flame at a specific wavelength. The wavelengths found in the atomic emission spectra help determine the element's identity. Notably, the intensity of the lines generated by the emitted light is proportional to the quantity of the element's atoms present in the sample.
Emission spectra are typically produced when a low-pressure gas's atoms are heated or otherwise excited, such as by a strong electric field.
When a granule of an ionic compound or a droplet of its solution is placed in a non-luminous flame, the electrons within absorb the flame's heat energy. This absorption causes the electrons to jump to higher energy levels - the energy absorbed must match the quantised energy difference between the orbits.
Due to the quantised nature of electron states, when an electron drops from a higher excited state to a lower one, it must emit a photon of energy corresponding to the energy difference between the two orbits. The frequency of the emitted photon is determined by the formula: E = hf. Here, higher energy photons correspond to a higher frequency (lower wavelength, i.e., the violet end of the visible spectrum). The larger the energy difference between the two shells, the greater the energy of the photon, and therefore, the higher its frequency.
Each element possesses a unique set of possible energy transitions. As a result, each has a unique emissions spectrum, which becomes visible when electrons release photons as they fall back to their ground state after excitation. Within the visible range, some of these emission spectra are remarkably intense, possibly composed of several closely spaced ones. The overall color is determined by the wavelengths of the emitted photons, which correspond to their color.
The frequencies of radiation emitted depend on the available energy transitions within the atom's energy levels. Since each element has a unique set of possible energy levels, excited atoms only emit certain frequencies of radiation that are specific to that element.
The continuous spectrum represents the entire range of wavelengths and frequencies of electromagnetic (EM) radiation. When white light is shone through a slit and then a prism, a continuous distribution of wavelengths becomes visible.
An emission spectrum is a pattern of colored lines superimposed on a dark background, with each line representing a photon released by an excited electron that has returned to a lower energy level, or its ground state. The energy of the photon corresponds to the difference between the two energy levels, and its frequency, given by E = hf, determines its color (where h is the Planck constant, and f is the frequency). As each element has different possible transitions within the atom's energy levels, the emission spectrum will be unique. When light passes through a narrow slit and then through a glass prism, the refraction of the light allows a spectrum of colored lines to appear on a darkened background behind it.
It's essential to note that each element will produce a unique emission spectrum that remains consistent for any sample of that same element. Diagrams below illustrate how emission spectra are produced, as well as the different spectra of various elements.
