Electron sheath

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As Electron sheath or also Atomic shell designates one the covering one , those exists that .

From the knowledge of the structure of the electron sheath leave themselves many physical and chemical characteristics of and thus characteristics from materials derive:

Atomic radius, Emission and of , Dipole moment.

In addition a connection between the structure of the electron sheath and the structure exists of the the chemical elements.

The development one the electron sheath is close with the development that Atomic theory and from it the developed and electron models links.

Structure

Core covering model of Rutherford

The covering of the atom is almost masslessly and electrically negatively charged. In the neutral atom the amount of the positive nuclear charge is equal to the amount of the charge of the covering

Quantization of the charge - elementary charge

That Millikan-Versuch (oil drop attempt) it resulted in that the charge of the atomic shell cannot take any amount. It knows only integral multiple of the elementary charge <math>e = -1{,}602\cdot10^{-19}</math> Coulomb amounted to. The same applies to the elementary charge of the core: it is positive and has the value <math>e = +1{,}602\cdot10^{-19}</math>C. The carriers of a positive elementary charge become mentioned, the carriers of the negative elementary charge are those .

Thus applies in a neutral atom:

The number that is correct in the atomic shell not with the number that in the atomic nucleus, then the atom is loaded, and becomes as Ion designated. The proton number is in the core more largely as the electron number, the atom is positively charged, it lies in forwards. Is the proton number smaller as the electron number, the atom is negatively charged, it lies in forwards.

Also ions can form:
Here the sum of all protons must be compared with the sum of all electrons of all atoms in the molecule: One speaks also here of cations, if a surplus of positive charge is present, and of anions with surplus of negative charge.
molecules, which are neutral outward, are the Atiomgruppen loaded differently however in different ranges exhibit (z. B. Amino acids).

In addition in a molecule the atoms can disturb the electron sheaths mutually, how Partialladungen develop, see Dipole.
Induced dipoles result from between-molecular reciprocal effect.

The Bohr atom model - quantum model

Quantization of the energy of the electrons in the atomic shell

The measurement of the ionization energies and the measurement of absorption and emission spectra result in that electrons of an atom exhibit different energies, D. h. different energy levels take.

From this bores its shell model developed, illustrated with the planet model:
Electrons take only certain main energy levels, which correspond to the individual concentrically electron shells arranged around the atomic nucleus in the shell model.

The main energy levels are designated by the principal quantum number n: n = 1 is the lowest main energy level. The bowls are named capital letters: the k-bowl corresponds the lowest energy level:

Principal quantum number bowl
-------------------------
       1 K
       2 L
       3 M
       4 N
       5 O
       6 P
       7 Q

With this model and its two Bohr postulates could bore of Johann Jakob Balmer by a formula described spectra of the hydrogen explain: The electrons are lifted by activation (energy input) of the atom on a higher energy level (bowl).

From there they jump back under sending of light to certain, lower conditions. Thus those corresponds Lyman series a return on the k-bowl, those Balmer series a return on the l-bowl, those Paschen-Serie a return on the m-bowl, those Brackett series a return on the n-bowl and those Pfund-Serie a return on the o-bowl.

Since other emission spectra could not be explained, they became after bore and Sommerfeld arranged into lower shells (Nebenenergieniveaus).

Fine structure of the main energy levels - under or Nebenniveaus

It resulted in precise measurements of ionization energies and spectra that the main energy levels are compound from Unterniveaus. These become in the shell model of the moved electron as interprets.

The Unterniveaus becomes with the small letters and/or. the azimuthal quantum number names l:

l = 0: S-level,
l = 1: P-level,
l = 2: D-level,
l = 3: F-level
l = 4: G-level
l = 5: H-level
etc..

The number of the Unterniveaus corresponds thereby to the respective principal quantum number:

Orbital one

With that Orbital model the conception of electrons moving on bowls must be finally given up:

Orbital ones are areas, in which electrons with a certain probability are.

The orbital is illustrated with the spatial representation of the wahrscheinlichkeitsdichte, itself with multiplication the that with their conjugated complexes to compute leaves.

Each Unterniveau consists the number of the orbital for each Unterniveau of orbitals, can with the formula 2*l+1 be computed.

In the orbital model a certain quantum state is assigned to each electron of an atom in the atomic shell, which is completely described by a sentence by 4 quantum numbers. Each electron of an atom must differ in at least one quantum number from all remaining electrons.
(in parentheses the data for the two electrons of the helium)

• n = principal quantum number (1/1)
• l = azimuthal quantum number, it gives the spatial shape of the orbitals on (0/0)
• m = magnetic quantum number, it indicates the spatial adjustment of the orbitals. (0/0)
• s = spin quantum number (+1/2/ 1/2)

A orbital knows only maximally two electrons with opposite in each case .

But can be appropriate for the s-s-Orbital within a main energy level several same orbital, whose electrons are on identical energy level, excluded the simplest orbitals.

see also:

Purchase to

Usually beginning a new orbital type is added, with the k-bowl with each bowl, in which there is only the 1s-Orbital. In addition each bowl has again the preceding orbital types, each bowl possesses thus z.B. their own s-s-Orbital.

However the energy levels of the D and f-orbital overlap with the energy level systematically actually of the higher s-orbital. This leaves "gaps" in in the 3. Period would have those 3. Nebengruppe begin, it continues to go along however in that 3. Main group.

3. Nebengruppe begins only in the 4. Period (= > 4. Main energy level = n-bowl) behind . The 3d-Orbitale with electrons is filled up only here.

The arrangement of the electron sheath becomes by those represented. Thus the elektronenkonfiguration means of the 1s²2s²2p⁴that the atom in the 1s-Orbital (1. S-s-Orbital, corresponds to the k-bowl) two electrons possesses, in the second bowl (l-bowl) is 6 electrons: 2 in the 2s and 4 in the 2p-Orbital.

The bowls have a maximum occupation number. From the inside outward the electron sheath is arranged into the following bowls (main energy levels):

• K-bowl, n = 1, (max. 2 electrons) (2 electrons in the 1s-Orbital: ß²)
• L-bowl, n = 2, (max. 8 electrons) (2 electrons in the 2s-Orbital and 6 electrons in the 2p-Orbital: 2s², 2p⁶)
• M-bowl, n = 3, (max. 18 electrons) (2 electrons in the 3s-Oribtal, 6 electrons in the 3p-Orbital and 10 electrons in the 3d-Oribtal: 3s², 3p⁶, 3d¹⁰)
• N-bowl, n = 4, (max. 32 electrons) (4s², 4p⁶, 4d¹⁰, 4f¹⁴)
• O-bowl, n = 5, (max. 50 electrons)
• P-bowl, n = 6, (max. 72 electrons)
• Q-bowl, n = 7, (max. 98 electrons)

The formula for the maximum occupation number reads: 2n², whereby n the principal quantum number is.

Application

The orbital model can be used outstanding for the forecast by chemical connections and characteristics, as well as Emmissionsspektren by atoms and molecules. For molecules leave themselves after that MO model Molecule orbital compute and measure.