You can read about atomic structure in How Atoms Work , but a quick recap here will be helpful. In , a Danish scientist by the name of Niels Bohr took Ernest Rutherford's model of the atom -- a dense nucleus surrounded by a cloud of electrons -- and made some slight improvements that better fit with experimental data.
In Bohr's model, the electrons surrounding the nucleus existed in discrete orbits, much like planets orbiting the sun. In fact, the classic visual image we all have of atoms, such as the one on the right, is modeled after Bohr's concept. Scientists have since moved away from some of Bohr's conclusions, including the idea of electrons moving around the nucleus in fixed paths, instead envisioning electrons congregating around the nucleus in a cloud.
In the Bohr atom, an electron in a particular orbit is associated with a specific amount of energy. Unlike planets, which remain fixed in their orbits, electrons can hop from one orbit to another.
An electron in its default orbit is in its ground state. To move from the ground state to an orbit farther away from the nucleus, an electron must absorb energy. When this happens, chemists say the electron is in an excited state. Electrons generally can't remain in an excited state indefinitely. Instead, they jump back down to the ground state, a move that requires the release of the same energy that enabled them to become excited in the first place.
This energy takes the form of a photon -- the tiniest particle of light -- at a certain wavelength and, because wavelength and color are related, at a certain color.
In other words, the electrons of one element exist in slightly different orbits than the electrons of another element. Because the internal structures of the elements are unique, they emit different wavelengths of light when their electrons get excited. The 2-dimensional spectra are easily extracted from this digital format and manipulated to produce 1-dimensional spectra like the galaxy spectrum shown below. The spectrum of an S7 spiral galaxy showing both emission and absorption line features.
Wavelength is measured in angstroms while the flux is in arbitrary units. Understanding these molecules and their behavior is the key to understanding the physical world around us. By using a technology called nuclear magnetic resonance NMR spectroscopy, scientists are able to see these molecules and magnify even their smallest details, observing how they behave in all types of matter.
Nuclear magnetic resonance spectroscopy is an analytical chemistry technique. It was first demonstrated in by Felix Bloch and Edward Mills Purcell, who subsequently shared the Nobel prize for their accomplishments and research in this field. The first commercial spectrometers were created in the s and quickly became an indispensable tool for research chemists.
These early spectrometers were expensive, bulky, and had a large footprint compared to the tabletop NMR and benchtop spectrometers used today. The first commercial spectrometers were based on conventional electromagnets and permanent magnets. By the s, superconducting magnets, such as those used in modern benchtop spectrometers, had been largely adopted as the standard by chemists.
There are a wide variety of NMR applications, and this technology particularly useful in the field of cancer research, where it's used for the development of smart delivery systems for cancer-treating drugs.
NMR can also help scientists understand the molecular basis for photosynthesis in plants and algae, making it possible to determine which crop strains are best suited to thrive in different environments.
Another application in which NMR spectrography shows usefulness is in the development of next generation batteries. To that end, portable NMR benchtop spectrometers play a crucial role in establishing the molecular details of a battery's energy-storing capability. When molecules are placed in a strong magnetic field, the nuclei of some atoms will begin to behave like small magnets. If a broad spectrum of radio frequency waves are applied to the sample, the nuclei will being to resonate at their own specific frequencies.
This is similar to the use of a tuning fork, where a guitar string will only resonate in response to a tone of the exact right frequency.
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