BBC Bitesize - Higher Physics - Spectra - Revision 2
Chemists describe the structure of atoms using models. photoelectric effect, absorption and emission spectra, quantum numbers, and electron configurations. The emitted light can be refracted by a prism, producing spectra with a distinctive striped Bohr's model of the hydrogen atom: quantization of electronic structure .. Since we also know the relationship between the energy of a photon and its. Atomic spectroscopy is the determination of elemental composition by its These levels have well defined energies and electrons moving between them must has a unique electronic structure, the wavelength of light emitted is a unique.Absorption and emission - Electronic structure of atoms - Chemistry - Khan Academy
A hot, diffuse gas produces bright spectral lines emission lines A cool, diffuse gas in front of a source of continuous radiation produces dark spectral lines absorption lines in the continuous spectrum. What is going on here? To understand this, we need two concepts: It can be characterized by wavelength and frequency.
Different wavelengths correspond to different colors, and ultimately different types of radiation UV, IR, radio, X-rays, etc. Light can also be characterized by discrete particles called photons -- hence the wave-particle duality of light.
How much energy is contained in a single photon?
Electronic structure of atoms | AP®︎ Chemistry | Science | Khan Academy
How fast does it move? How much mass does it have? How was this discovered? Via the photoelectric effect: The following are his key contributions to our understanding of atomic structure: Electrons can occupy only certain regions of space, called orbits.
Electronic structure of atoms
Orbits closer to the nucleus are lower in energy. Electrons can move from one orbit to another by absorbing or emitting energy, giving rise to characteristic spectra. Unfortunately, Bohr could not explain why the electron should be restricted to particular orbits. Also, despite a great deal of tinkering, such as assuming that orbits could be ellipses rather than circles, his model could not quantitatively explain the emission spectra of any element other than hydrogen Figure 6.
Scientists needed a fundamental change in their way of thinking about the electronic structure of atoms to advance beyond the Bohr model. Thus far we have explicitly considered only the emission of light by atoms in excited states, which produces an emission spectrum A spectrum produced by the emission of light by atoms in excited states. The converse, absorption of light by ground-state atoms to produce an excited state, can also occur, producing an absorption spectrum A spectrum produced by the absorption of light by ground-state atoms.
Because each element has characteristic emission and absorption spectra, scientists can use such spectra to analyze the composition of matter, as we describe in Section 6.
Note the Pattern When an atom emits light, it decays to a lower energy state; when an atom absorbs light, it is excited to a higher energy state. If the light that emerges is passed through a prism, it forms a continuous spectrum with black lines corresponding to no light passing through the sample at,and nm.
Any given element therefore has both a characteristic emission spectrum and a characteristic absorption spectrum, which are essentially complementary images.
Absorption of light by a hydrogen atom. Atomic emission using electrical arcs has been widely used in qualitative analysis. Emission techniques can also be used to determine how much of an element is present in a sample.
For a "quantitative" analysis, the intensity of light emitted at the wavelength of the element to be determined is measured. The emission intensity at this wavelength will be greater as the number of atoms of the analyte element increases.
The technique of flame photometry is an application of atomic emission for quantitative analysis. This technique incorporates aspects of both atomic absorption and atomic emission.
Like atomic absorption, ground state atoms created in a flame are excited by focusing a beam of light into the atomic vapor. Instead of looking at the amount of light absorbed in the process, however, the emission resulting from the decay of the atoms excited by the source light is measured.
The intensity of this "fluorescence" increases with increasing atom concentration, providing the basis for quantitative determination. The source lamp for atomic fluorescence is mounted at an angle to the rest of the optical system, so that the light detector sees only the fluorescence in the flame and not the light from the lamp itself.
It is advantageous to maximize lamp intensity since sensitivity is directly related to the number of excited atoms which in turn is a function of the intensity of the exciting radiation.
While atomic absorption is the most widely applied of the three techniques and usually offers several advantages over the other two, particular benefits may be gained with either emission or fluorescence in special analytical situations.