Electron shells subshell filling

The nomenclature for X-ray emission consists of the name of the shell in which the vacancy was created (K, L, M, N), and on the electronic shell that filled the vacancy. For instance, ejection of a K shell electron, filled with a L shell electron is denoted as K if filled with an M shell electron, then Kp is used, and so on. Due to electronic subshells, nomenclature becomes significantly complex, as shown in Figure 7.19. 

Since the possible numerical values of / depend on the value of n, the number of subshells within a given shell is determined by the value of n. The number of subshells within a given shell is merely the value of rt, the shell number. Thus, the first shell has one subshell the second shell has two subshclls, and so forth. These facts are summarized in Table 17-4. Even the atoms with the most electrons do not have enough electrons to completely fill the highest shells shown. The subshells that hold electrons in the ground states of the biggest atoms are boldfaced. 

Fill the sub-shells in this order. Put two electrons in each s sub-shell, six in each p sub-shell, and ten in each d subshell until there are not enough electrons left to fill the next orbital. 

As in the case of the orbital angular momentum, the upper case 5 here signifies the total spin angular momentum of aU the unpaired electrons in the atom outside of closed shells. The filled, inner subshells contribute nothing to 5. It follows that if the configuration has only a single electron that is not in a filled subsheU, the 5 quantum number is simply the quantum number for the single electron. 

The term symbol S, n, A. .., analogous to the atomic S, P, D... symbolizes the axial component of the total orbital angular momentum. When a tt-shell is filled (four electrons) or half-filled (two electrons), the orbital angular momentum cancels to zero and we find a E term. The spin multiplicity is completely analogous to the atomic case. The total parity is again designated by a subscript g or u. Since the many-electron wavefimction is made up of products of individual MO s, the total parity is odd only if the molecule contains an odd number of u orbitals. Thus, a (Ty - or a 7r -subshell transforms like g. 

The major trend is for decreasing radius as the nuclear charge increases, with the exception that Cu and Zn begin to show the effects of electron-electron repulsions and become larger as the <7-subshell becomes filled. Mn is also an exception as found for other properties this may be attributed to having the /-shell half-filled. 

Nitrogen has seven electrons, which occupy the lowest energy orbitals available. Two electrons can occupy the first shell, w = 1, in which there is only one r orbital when w = 1, then f must be zero, and therefore = 0. The two electrons differ only in spin quantum number, m. The next five electrons can all fit into the second shell, for which n = 2 and i may be either 0 or 1. The i = 0 (s) subshell fills first, and the ( = I (p) subshell is occupied next. 

For atoms with three or more electrons, the electrons in a given shell are shielded by electrons in inner shells (that is, shells closer to the nucleus) but not by electrons in outer shells. Thus, in a neutral lithium atom, whose electron configuration is s 2s, the 2s electron is shielded by the two Is electrons, but the 2s electron does not have a shielding effect on the 1 electrons. In addition, filled inner shells shield outer electrons more effectively than electrons in the same subshell shield each other. 

The periodic table may be related to the electron shell structure of any element. The table may be divided up into blocks corresponding to the subshell designation of the most recent orbital to be filled by the building-up rule. 

We divide the levels into shells, those levels with the same value of the principal quantum number, and subshells, those within a shell that have the same value of the azimuthal quantum number. For a specified value of /, there are 2/ + 1 values of m for a specified value of m, the electron may have two values of m. Hence there are 2(2/ -hi) distinct combinations of m and m. This is the maximum number of electrons permitted in any subshell. For an s subshell, / = 0, so only two electrons may occupy the subshell. For a p subshell, I = 1, and six electrons are required to fill the p subshell. Ten electrons fill a d subshell, I = 2, and so on. The shell with n = 1, is the K shell that with n = 2, the L shell n = 3, the M shell and so on. The number of electrons required to fill the shells is shown in Table 22.4. The numbers 2, 8, 18, 32,... in the last column are given by 2n, where n is the principal quantum number. The numbers in this famous sequence are the numbers of elements in the periods of the periodic table. 

Value of n Subshells present Number of electrons in the filled shell... 

The calculation confirms that the magic numbers are due to the closing of electronic shells The levels are filled in the order Is, Ip, Id, 2s, If, 2p, Ig, 2d, Ih, 3s... Filling these levels with the maximum number of electrons allowed leads to the subshell closing numbers 2,8,18,20,34,40,58,68,90,92,... The number N = 34, which appears after filling the If level is a magic number of secondary importance, that is also observed in the experiments. On the other hand the... 

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