Magnetochemistry
The magneto chemistry is a branch of physical chemistry that deals with the magnetic properties of materials or substances. It was founded around 1905 by French physicist Paul Langevin and developed by the German chemist Wilhelm Klemm.
Determination of the effects
The measurement of the magnetic susceptibility and the magnetic moment allows conclusions about the electron configurations of metal ions or non-metallic molecules. In a simple way magneto- chemical effects on the magnetic susceptibility with a Gouyschen scale can be determined. Other similar methods of determination of the susceptibility Quincke or after Faraday Curie based on the weight and magnetic field change.
Many chemical substances show by the influence of a magnetic field, an alignment that is directly measurable as a change in weight. Clearly, one imagines the individual atoms as small elementary magnets before, which - like many small iron filings - align in a magnetic field. Depending on the class of a small measurable interaction shows the magnetic field ( diamagnetism ), a stronger interaction ( paramagnetism ) or a very strong interaction ( ferromagnetism ). As an idea, a small circular electric motion of an electron around its own axis can be assumed to be induced by a magnet. By the influence of a magnet on a current loop, a current-carrying coil and a magnetic dipole moment is generated, the vector perpendicular to the plane of the circulating current is flowing ( right-hand rule). Analogous rotational movement is generated in each magnetic field to a magnetically active substance to each elementary electron. When the vector of the magnetic dipole moment is not coincident with the direction vector of the magnetic field, there is centrifugal movements of the elementary magnets.
Mathematically, the torque of elementary magnets described by the vector product of the magnetic dipole moment and the magnetic field. The vector product is in mathematics at the perpendicular to a plane of two vectors and corresponds to the length of its vector, the projected surface area of both vectors.
The intensity of the influence of substances through a magnetic field can be determined by weighing. As a very important magneto- chemical parameter applies the magnetic susceptibility. Using a neodymium magnet and a fine scale can be roughly determined the magnetic susceptibility by the method of Cortel.
The weight change is the change in force is directly proportional. The change in force by individual magneto chemical substances is specified with the substance-specific susceptibility ( ). This is a proportionality factor without units. Often, however, the susceptibility to the density of the material substance ( number of moles of substance per cubic meter molar susceptibility ) with respect, only by the terms of the density, substances can be compared.
Magnetic flux density and magnetic field strength are linked by the following relationship:
B = magnetic flux density (kg * s -2 * A-1)
H = magnetic field strength ( A / m)
= Permeability of vacuum ( 1.256 * 10-8 m * kg/C2 )
If negative, it is a diamagnetic substance; is positive, it is a paramagnetic substance. At very high values are ferromagnetic substances. These substances actually have a magnetization without the presence of a magnetic field.
After gouyschen principle, one introduces a paramagnetic sample between the poles of two strong permanent magnets. In this case, reverse magnetic field is induced by the elementary magnets of the sample a, the applied magnetic field. Since the force is directed perpendicular to the applied magnetic field, the sample is lightly pushed upward. The force is measured using a scale. With correct determination of the field strength at the sample surface in the inlet and outlet, the susceptibility of the material, by the force of gravity with the equation:
F = 0.5 * () * A ** ( HE2 - HA2 )
HE: field strength at sample entry
HA: field strength at the sample outlet
A: area of a uniformly thick specimen
Be determined.
The same equation is also applicable to the study of substances by means of a neodymium magnet.
In the optical range, para-and diamagnetism can also be detected. Man filling a crystal ( see also: Newton's rings ) with a solution of a paramagnetic substance and represents the acute angle between the crystal arriving on the pole pieces of two mutually attracting permanent magnets. Beam is a beam of light parallel to the pole pieces on the sample, the incident on the substance beams are separated into two beams and are visible on the opposite to the incident light side of the wall. At diamagnetic substances, the beam is compressed.
Based on the magnetic field strength of the magnet, the specific density of the charged substance and the weight change can determine the magnetization. Paramagnetic substances have the ambition, in the region of high field strengths to wander (for example, two round magnets in the center of the circle ), diamagnetic substances migrate into the region of low field strengths (for example, two round magnets to the edges of the circle). The paramagnetism is temperature dependent, the diamagnetism is not.
Causes
The cause of the susceptibility is in the single-electron around the nucleus. To understand the effect, one can assume standard model that unpaired electrons rotate in a circular orbit around the atomic nuclei, similar to a current-carrying coil, thereby generating a magnetic field. To lift the individual spins, ie the electron orbitals of the molecule or atom with two electrons in opposite directions replenished (eg noble gases or noble gas-like ions Na , Ca2 , Cl- ), the substance has no electron spin and is diamagnetic. The diamagnetic susceptibility is always negative and significantly smaller (factor: 0.01 to 0.1 ) than the paramagnetic susceptibility. In paramagnetic materials, there are unpaired electrons. From Table works on the electron configuration of elements or of the orbital theory of molecules can be the number of unpaired electrons determine (for example, the hydrogen atom, the Fe ( II ) four and in Cu ( II), two unpaired electrons) and, the magnetic moment (for example, the iron group metals or the lanthanides of the spin relationship m = (n * (n 2) ) -0,5 ) calculated.
Measurements
By magneto chemical measurements structural issues such as the oxidation number or the type of bond can be clarified. Thus, FeSO4 and [Fe (H2O ) 4] Cl2 a magnetic moment of about 5.2 mB, however, K4 [Fe (CN ) 6] and Fe ( CO) 5, a magnetic moment of zero. While in the former an ionic structure between cation and ligand is present in the latter a highly polarized bond is present.
Results
- In inorganic chemistry the magnetochemistry has made important contributions to the development of ligand field theory and to the understanding of the metallic state.
- In organic chemistry magneto- chemical measurements for the detection of polymerization processes are used ( the gradual disappearance of double bonds is magneto detected chemically ), for the measurement of aromaticity and organic radicals.
- In addition to the slide and paramagnetic materials, there are also materials which show ferromagnetic, antiferromagnetic or ferrimagnetic behavior. When the action of a magnetic field, the magnetization takes with them too much or they themselves become permanent magnets.
- By means of the magneto chemistry, important theoretical basis for NMR spectroscopy are placed. However Kernsuszeptibilität is by a factor of 104 smaller than the diamagnetic susceptibility, so that the Kernsuszeptibilität is not detectable by weighing.