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A moving electron around the nucleus can be likened to the elementary electric current; it generates a magnetic field. The magnetic fields of different electrons, folding to form a magnetic field of the atom. To introduce the characteristics of a vector quantity called the magnetic moment. If the electrons completely fill a particular shell (Is, 2s, 2p, etc.), their magnetic fields cancel each other, the magnetic moments of the atoms are zero.
In 1922 in Germany, O. Stern and W. Gerlach performed experience has shown that the magnetic moment of an atom of space is quantized. They sent a beam of atoms having a magnetic moment, through an inhomogeneous magnetic field and investigated the deflection of atoms under the influence of the field. The extent and nature of the deviation depends on the orientation of the magnetic moment of an atom relative to the direction of the field. If the atoms in the beam were with various orientations of magnetic moments, we observed a continuous angular "smearing" of the original beam. In the experiment also observed a clear splitting of the atom beam into several beams, and this meant that the magnetic moment along the magnetic field can have only certain specific (discrete) values. Let us turn to the distribution of the deviations of the sodium atoms in an inhomogeneous magnetic field (it was obtained in 1930). This distribution has two distinct maxima. In the sodium atom, three filled shells (Is, 2s, 2p) and one Ss-electron. The electron cloud of s-electrons is spherically symmetric, so their movement in the nuclear field does not lead to the appearance of the magnetic moment. To explain the observed splitting of the beam of sodium atoms into two components, we must assume that the electron has intrinsic magnetic moment that is not associated with the motion of an electron
around the nucleus. This magnetic moment is conventionally associated with the rotation of the electron around its own axis and is called spin angular momentum. The magnetic moment of the electron associated with its motion around the nucleus, called the orbital angular momentum. The fact that a splitting into two beams, means that the spin of the electron has two projections on the direction of the magnetic field. |