Energy level interleaving meansElectronic layerThe energy of some orbits with large numbers is lower thanNumber of electronic layersThe phenomenon of smaller energies in certain orbits.
Transitional elementOuter layer of scandiumElectronic layout4s^two∣3d^oneWhen electrons are lost, 3d electrons should be lost first according to energy level interleaving, which becomes 4s^two∣3d^zero, and fromAtomic spectrumThe experiment shows that the electrons on the 4s are lost first to become 4s^one∣3d^one。
This is because the existence of 3d electrons weakens the attraction of 4s electrons in the atomic nucleus and is easy to lose.When the transition elements are ionized, they generally lose ns electrons first, but some, such as yttrium, also lose (n-1) d electrons first.The order of energy level interleaving is not absolutely constantAtomic numberIn large atoms, the energy of the 3d orbit may be higher than that of the 4s orbit.
Similar to 3d and 4sNucleusThe phenomenon that the arrangement of external electrons on the energy level is staggered is called energy level interleaving[1]。
Law summary
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1： The rule that electrons fill the outermost ns first, then (n-1) d in the secondary outer layer, or even (n-2) f in the penultimate layer is called“Energy level interleaving”
2： IfPrincipal quantum numberN and the angular quantum number l are different. Although the energy level is basically determined by the size of n, sometimes it is highElectronic layerlow SublayerThe energy of (e.g. 4s) is lower than that of the high sublayer (e.g. 3d) in some low electron layersEnergy level interleaving。Energy level interleaving is due toNuclear chargeIncrease, the gravity of the nucleus electron increases, and the energy of each sublayer decreases, but the decrease amplitude is different.Energy level interleaving affects the distribution of electrons in atoms. "
IIIEnergy level interleavingMeansNumber of electronic layersThe energy of some larger orbits is lower than that of some smaller electron layersOrbital energyPhenomenon.If the energy of 4s is smaller than that of 3d, the electrons should be filled for 4s before filling the 3d orbit.Transitional elementOuter layer of scandiumElectronic layoutIt is 4s23d1. When electrons are lost, 3d electrons should be lost first according to the energy level interleaving, becoming 4s23d0Atomic spectrumThe experiment shows that the electrons on the 4s are lost first and become 4s13d1.This is because the existence of 3d electrons weakens the attraction of 4s electrons in the atomic nucleus and is easy to lose.When the transition elements are ionized, they generally lose ns electrons first, but some, such as yttrium, also lose (n-1) d electrons first.The order of energy level interleaving is not absolutely constantAtomic numberIn large atoms, the energy of the 3d orbit may be lower than that of the 4s orbit.
In a nutshell, the shielding effect is caused by the interaction of electrons. At the same time, the larger the n is, the greater the average distance between the electron and the nucleus, the greater the potential energy, and the higher the orbital energy.
Penetration effectnamelywave functionThere are n-l peaks in the radial direction. When n phase is in, the smaller the l is, the more the peaks are. The deeper the first peak is drilled, and the lower the potential energy is. When n phase is in, the larger the l is, the higher the orbital energy is.
Energy level interleaving
When n and l change comprehensively, it is generally seen as follows:
For the outer electrons of the atom, the larger the n+0.7l, the higher the energy
For the outer electrons of ions, the larger the n+0.4l, the higher the energy
For atoms or ionsInner electron, the greater the n, the higher the energy
This results in that the energy levels are not necessarily arranged according to the size of n.
2. Sum of principal quantum numbersAngular quantum numberWhen the sum is equal, the larger the principal quantum number, the higher the energy
For example, the sum of the main quantum number and the angular quantum number of the 4s orbit is 4, and the sum of the main quantum number and the angular quantum number of the 3d orbit is 5, so the energy of the 4s orbit is lower than the energy of the 3d orbit;The sum of the principal quantum numbers and angular quantum numbers of the 3d and 4p orbits is 5, but the principal quantum numbers of the 4p orbits are larger, so the energy of the 4p orbits is higher than that of the 3d orbits
stayNucleusThe electrons with a higher probability of appearing nearby can avoid the shielding of other electrons more and get closer to the nucleus due to the strong attraction of the nucleus. This effect of entering the internal space of the atom is called the penetration effect.Penetration and atomic orbitalRadial distribution functionofThe smaller the number of orbital radial distribution functions, the deeper the first peak is drilled and the closer it is to the nucleus.It can be seen from the figure that 2s has one more small peak closer to the nucleus than 2p, which indicates that 2s electrons have stronger penetration ability than 2p electrons, so they are less shielded and have lower energy than 2p.
AndShielding effectOn the contrary, the outer electrons havePenetration effect。Outer layerAngular quantum numberElectrons on small energy levels, such as 4s electrons, can drill into the inner space near the nucleus to move, so that they are less shielded by other electrons, and are strongly attracted by the nucleus, so the electron energy decreases, resulting in E (4s)<E (3d).
Represented by a small circle in the figureAtomic orbital, several orbits in the box have similar energies, called oneEnergy level group。Between adjacent energy level groupsEnergy differenceLarge, the energy difference of the same energy level group is small.There are seven such energy level groups, each of which is based onS trackStart withP OrbitIt's over.It is related toperiodic tableThe seven cycles in the[2]。
In the figure, there is only one circle in the s layer, indicating that there is only one atomic orbit;There are three circles in the p-layer, indicating that there are three atomic orbitals.Since these three p orbitals have the same energy, they are calledDegenerate orbitOr equivalent orbit.Similarly, there are five orbits with the same energy in the d layer, that is, the d orbit isQuintuple degeneracyOf;There are seven orbits with the same energy in the f layer, that is, the f orbit is seven fold degenerate.
N+0.7l rule
Famous chemist in ChinaXu GuangxianMr. Li proposed the (n+0.7l) approximation law for orbital energy.He believes that the order of orbital energy can be judged by the value of (n+0.7l), and the order of numerical values corresponds to the order of orbital energy.The energy levels with the same number of first places are also classified into oneEnergy level group, and launched withAtomic numberAdd, the order of filling electrons in the orbit is
For example, if the last electron of K atom is filled in the 3d or 4s orbitAtomic energyLower?Since (3+0.7 × 2)>(4+0.7 × 0), electrons should be filled in the 4s orbit.This approximation law gives the same energy level order and grouping results as Pauling[3]。
1962 American inorganic structural chemist F.ACotton）Summarize the elements in the periodic table in the simplest wayAtomic orbitalEnergy varies withAtomic numberThe increase rule is shown in Figure 6-17.In the figureAbscissaIs the atomic number,OrdinateIs the orbital energy.It can be seen from the figure that the atomic number ofhydrogen atomThe orbital energy is only related to the n value.When n value is the sameDegenerate orbit。However, with the increase of atomic number and nuclear charge, the attraction of nucleus electrons also increases, which makes the energy of various orbits decrease by 3.From FigureThe energy level interleaving phenomenon near the atomic numbers 19 (K) and 20 (Ca) can be clearly seen in.From the enlarged view, it is clearer to see that the energy of 3d from Sc is less than 4s.And inapproximate energy level diagram This has not been reflected in[4]。
