Quantum NumbersGeneral rule of Electron construction

The electron configuration of an atomic varieties (neutral or ionic) enables us to recognize the shape and also energy the its electrons. Plenty of general rules space taken into consideration when assigning the "location" the the electron come its prospective power state, but these assignments room arbitrary and it is always uncertain as to which electron is being described. Learning the electron construction of a types gives united state a far better understanding that its bonding ability, magnetism and also other moment-g.comistry properties.

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The electron configuration is the typical notation provided to define the digital structure of one atom. Under the orbital approximation, we let every electron occupy an orbital, which can be fixed by a solitary wavefunction. In law so, we achieve three quantum number (n,l,ml), which room the very same as the ones acquired from addressing the Schrodinger"s equation because that Bohr"s hydrogen atom. Hence, numerous of the rules the we usage to describe the electron"s resolve in the hydrogen atom can also be used in systems including multiple electrons. When assigning electron to orbitals, we need to follow a set of three rules: the Aufbau Principle, the Pauli-Exclusion Principle, and also Hund"s Rule.

The wavefunction is the solution to the Schrödinger equation. By addressing the Schrödinger equation because that the hydrogen atom, we attain three quantum numbers, namely the major quantum number (n), the orbital angular inert quantum number (l), and also the magnetic quantum number (ml). Over there is a 4th quantum number, dubbed the spin magnetic quantum number (ms), i m sorry is not derived from addressing the Schrödinger equation. Together, these 4 quantum numbers can be supplied to describe the location of an electron in Bohr"s hydrogen atom. This numbers have the right to be assumed of together an electron"s "address" in the atom.


To assist describe the suitable notation because that electron configuration, it is finest to carry out so v example. For this example, us will usage the iodine atom. There room two means in i beg your pardon electron configuration deserve to be written:

I: 1s22s22p63s23p64s23d104p65s24d105p5


I: 5s24d105p5

In both that these species of notations, the stimulate of the power levels should be composed by boosted energy, reflecting the variety of electrons in every subshell as an exponent. In the short notation, you ar brackets approximately the preceding noble gas element followed through the valence covering electron configuration. The routine table shows that kyrpton (Kr) is the vault noble gas listed before iodine. The noble gas configuration encompases the power states reduced than the valence covering electrons. Therefore, in this situation =1s22s22p63s23p64s23d104p6.

Principal Quantum Number (n)

The major quantum number n shows the shell or energy level in which the electron is found. The worth of n can be collection between 1 to n, whereby n is the worth of the outermost covering containing one electron. This quantum number deserve to only it is in positive, non-zero, and integer values. That is, n=1,2,3,4,..

For example, an Iodine atom has its outmost electron in the 5p orbital. Therefore, the principle quantum number for Iodine is 5.

Orbital Angular inert Quantum Number (l)

The orbital angular inert quantum number, l, suggests the subshell the the electron. You can likewise tell the form of the atom orbital v this quantum number. One s subshell corresponds to l=0, a p subshell = 1, a d subshell = 2, a f subshell = 3, and so forth. This quantum number have the right to only be positive and also integer values, return it have the right to take on a zero value. In general, because that every value of n, there are n values of l. Furthermore, the worth of l ranges from 0 to n-1. Because that example, if n=3, l=0,1,2.

So in regards come the example used above, the l values the Iodine because that n = 5 are l = 0, 1, 2, 3, 4.

Magnetic Quantum Number (ml)

The magnetic quantum number, ml, represents the orbitals the a provided subshell. For a offered l, ml can variety from -l come +l. A p subshell (l=1), because that instance, can have 3 orbitals corresponding to ml = -1, 0, +1. In other words, it specifies the px, py and also pzorbitals the the ns subshell. (However, the ml number don"t necessarily exchange mail to a given orbital. The truth that there are three orbitals simply is indicative of the 3 orbitals that a ns subshell.) In general, because that a provided l, there are 2l+1 possible values for ml; and also in a n primary shell, there are n2 orbitals found in that energy level.

Continuing on native out instance from above, the ml worths of Iodine space ml = -4, -3, -2, -1, 0 1, 2, 3, 4. These arbitrarily correspond to the 5s, 5px, 5py, 5pz, 4dx2-y2, 4dz2, 4dxy, 4dxz, and also 4dyz orbitals.

Spin Magnetic Quantum Number (ms)

The rotate magnetic quantum number deserve to only have a worth of one of two people +1/2 or -1/2. The worth of 1/2 is the turn quantum number, s, which explains the electron"s spin. Due to the rotate of the electron, it generates a magnetic field. In general, an electron v a ms=+1/2 is called ­­an alpha electron, and one through a ­ms=-1/2 is dubbed a beta electron. No two paired electrons have the right to have the very same spin value.

Out that these four quantum numbers, however, Bohr postulated that just the major quantum number, n, determines the energy of the electron. Therefore, the 3s orbital (l=0) has actually the same energy as the 3p (l=1) and 3d (l=2) orbitals, regardless of a difference in l values. This postulate, however, holds true only for Bohr"s hydrogen atom or other hydrogen-like atoms.

When taking care of multi-electron systems, us must think about the electron-electron interactions. Hence, the previously defined postulate breaks down in that the power of the electron is now established by both the principal quantum number, n, and the orbit angular momentum quantum number, l. Back the Schrodinger equation because that many-electron atom is extremely daunting to settle mathematically, we deserve to still describe their electronic structures via electron configurations.

General rule of Electron Configuration

There are a collection of basic rules that are supplied to figure out the electron construction of an atom species: Aufbau Principle, Hund"s Rule and the Pauli-Exclusion Principle. Before continuing, it"s vital to recognize that every orbital can be occupied by two electron of opposite spin (which will be further discussed later). The following table shows the possible variety of electrons that can occupy every orbital in a provided subshell.

subshell number the orbitals total variety of possible electron in each orbital
s 1 2
p 3 (px, py, pz) 6
d 5 (dx2-y2, dz2, dxy, dxz, dyz) 10
f 7 (fz3, fxz2, fxyz, fx(x2-3y2), fyz2, fz(x2-y2), fy(3x2-y2)


Using our example, iodine, again, we watch on the regular table the its atomic number is 53 (meaning it has 53 electrons in the neutral state). Its finish electron construction is 1s22s22p63s23p64s23d104p65s24d105p5. If you counting up all of these electrons, girlfriend will check out that that adds approximately 53 electrons. Notice that each subshell can only save the max lot of electron as shown in the table above.

Aufbau Principle

The native "Aufbau" is German because that "building up". The Aufbau Principle, also called the building-up principle, states that electron"s accounting orbitals in bespeak of boosting energy. The order of occupation is as follows:



Hund"s rule states that when electrons accounting degenerate orbitals (i.e. Very same n and l quantum numbers), they must first occupy the empty orbitals before dual occupying them. Furthermore, the most stable configuration results when the spins are parallel (i.e. All alpha electron or all beta electrons). Nitrogen, because that example, has actually 3 electron occupying the 2p orbital. Follow to Hund"s Rule, castle must an initial occupy every of the three degenerate p orbitals, namely the 2px orbital, 2py orbital, and the 2pz orbital, and also with parallel spins (Figure 2). The configuration listed below is incorrect because the third electron rectal does no occupy the north 2pz orbital. Instead, it rectal the half-filled 2px orbital. This, therefore, is a violation the Hund"s ascendancy (Figure 2).

Figure 2. A visual representation of the Aufbau Principle and also Hund"s Rule. Keep in mind that the filling of electron in each orbital(px, py and also pz) is arbitrary as long as the electrons are singly filled before having two electrons occupy the exact same orbital.(a)This diagram to represent the correct filling the electrons for the nitrogen atom. (b) This diagramrepresents the incorrectfilling of the electrons for the nitrogen atom.

Electronic construction of Cations and Anions

The method we designate digital configurations because that cations and also anions is essentially similar to the for neutral atom in their ground state. That is, us follow the three crucial rules: Aufbau Principle, Pauli-exclusion Principle, and also Hund"s Rule. The electronic configuration of cations is assigned by remove electrons an initial in the outermost ns orbital, complied with by the s orbital and also finally the d orbitals (if any an ext electrons need to be removed). Because that instance, the floor state digital configuration that calcium (Z=20) is 1s22s22p63s23p64s2. The calcium ion (Ca2+), however, has two electron less. Hence, the electron configuration for Ca2+ is 1s22s22p63s23p6. Because we need to take away two electrons, we very first remove electrons from the outermost shell (n=4). In this case, all the 4p subshells are empty; hence, we start by removing indigenous the s orbital, i m sorry is the 4s orbital. The electron configuration for Ca2+ is the same as the for Argon, which has 18 electrons. Hence, we deserve to say that both room isoelectronic.

The electronic configuration the anions is assigned by including electrons follow to Aufbau Principle. We include electrons to fill the outermost orbital the is occupied, and then add much more electrons come the next greater orbital. The neutral atom chlorine (Z=17), for instance has actually 17 electrons. Therefore, its ground state digital configuration deserve to be created as 1s22s22p63s23p5. The chloride ion (Cl-), top top the various other hand, has an additional electron for a full of 18 electrons. Complying with Aufbau Principle, the electron occupies the partly filled 3p subshell first, making the 3p orbital totally filled. The digital configuration for Cl- can, therefore, be designated as 1s22s22p63s23p6. Again, the electron configuration for the chloride ion is the exact same as the for Ca2+ and Argon. Hence, they space all isoelectronic to each other.


1. Which of the princples explained above tells united state that electron that room paired cannot have the same spin value?

2. Find the values of n, l, ml, and also ms for the following:

a. Mg

b. Ga

c. Co

3. What is a possible combination for the quantum number of the 5d orbital? Give an instance of an element which has the 5d orbital together it"s most outer orbital.

4. I m sorry of the complying with cannot exist (there might be more than one answer):

a. N = 4; l = 4; ml = -2; multiple sclerosis = +1/2

b. N = 3; l = 2; ml = 1; multiple sclerosis = 1

c. N = 4; l = 3; ml = 0; multiple sclerosis = +1/2

d. N = 1; l = 0; ml = 0; multiple sclerosis = +1/2

e. N = 0; l = 0; ml = 0; multiple sclerosis = +1/2

5. Compose electron configurations because that the following:

a. P

b. S2-

c. Zn3+


1. Pauli-exclusion Principle

2. A. N = 3; l = 0, 1, 2; ml = -2, -1, 0, 1, 2; ms deserve to be one of two people +1/2 or -1/2

b. N = 4; l = 0, 1, 2, 3; ml = -3, -2, -1, 0, 1, 2, 3; ms have the right to be either +1/2 or -1/2

c. N = 3; l = 0, 1, 2; ml = -2, -1, 0, 1, 2, 3; ms deserve to be either +1/2 or -1/2

3. N = 5; l = 3; ml = 0; multiple sclerosis = +1/2. Osmium (Os) is an example.

4. A. The worth of l cannot be 4, due to the fact that l varieties from (0 - n-1)

b. Ms can only be +1/2 or -1/2

c. Okay

d. Okay

e. The value of n cannot be zero.

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5. A. 1s22s22p63s23p3

b. 1s22s22p63s23p6

c. 1s22s22p63s23p64s23d7


Atkins, P. W., & De Paula, J. (2006). Physical moment-g.comistry because that the Life Sciences. brand-new York, NY: W. H. Freeman and also Company. Petrucci, R. H., Harwood, W. S., & Herring, F. G. (2002). General moment-g.comistry: principles and modern-day Applications. top Saddle River, NJ: Prentice-Hall, Inc. Shagoury, Richard. moment-g.comistry 1A class Book. 4th Ed. Custom Publishing. 2006. Print