Quantum NumbersGeneral rules of Electron configuration

The electron configuration of one atomic varieties (neutral or ionic) permits us to know the shape and also energy of its electrons. Countless general rules are taken into consideration when assigning the "location" that the electron come its prospective power state, but these assignments space arbitrary and it is always uncertain regarding which electron is being described. Learning the electron configuration of a species gives us a better understanding of its bonding ability, magnetism and other civicpride-kusatsu.netical properties.

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The electron configuration is the typical notation offered to define the electronic structure of an atom. Under the orbital approximation, we let each electron occupy an orbital, which have the right to be addressed by a single wavefunction. In act so, we obtain three quantum numbers (n,l,ml), which space the very same as the ones obtained from fixing the Schrodinger"s equation for Bohr"s hydrogen atom. Hence, plenty of of the rules that we use to explain the electron"s deal with in the hydrogen atom can likewise be provided in systems including multiple electrons. When assigning electrons to orbitals, we should follow a collection of 3 rules: the Aufbau Principle, the Pauli-Exclusion Principle, and also Hund"s Rule.

The wavefunction is the solution to the Schrödinger equation. By fixing the Schrödinger equation for the hydrogen atom, we attain three quantum numbers, namely the primary quantum number (n), the orbital angular momentum quantum number (l), and the magnetic quantum number (ml). There is a 4th quantum number, dubbed the turn magnetic quantum number (ms), i beg your pardon is not derived from solving the Schrödinger equation. Together, these four quantum numbers can be used to explain the location of an electron in Bohr"s hydrogen atom. This numbers deserve to be thought of as an electron"s "address" in the atom.


To help describe the appropriate notation because that electron configuration, the is best to perform so through example. Because that this example, us will usage the iodine atom. There are two means in i m sorry electron configuration have the right to be written:

I: 1s22s22p63s23p64s23d104p65s24d105p5


I: 5s24d105p5

In both that these species of notations, the bespeak of the energy levels have to be written by increased energy, showing the variety of electrons in every subshell together an exponent. In the quick notation, you place brackets roughly the preceding noble gas facet followed by the valence shell electron configuration. The regular table mirrors that kyrpton (Kr) is the vault noble gas noted before iodine. The noble gas configuration encompases the energy states reduced than the valence shell electrons. Therefore, in this case =1s22s22p63s23p64s23d104p6.

Principal Quantum Number (n)

The primary quantum number n indicates the covering or energy level in i m sorry the electron is found. The value of n deserve to be set between 1 to n, wherein n is the value 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, one Iodine atom has its outmost electron in the 5p orbital. Therefore, the rule quantum number for Iodine is 5.

Orbital Angular momentum Quantum Number (l)

The orbit angular momentum quantum number, l, indicates the subshell the the electron. Girlfriend can additionally tell the shape of the atom orbital v this quantum number. One s subshell synchronizes to l=0, a p subshell = 1, a d subshell = 2, a f subshell = 3, and also so forth. This quantum number can only it is in positive and also integer values, back it have the right to take ~ above a zero value. In general, because that every value of n, there room n worths of l. Furthermore, the worth of l varieties from 0 come n-1. For example, if n=3, l=0,1,2.

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

Magnetic Quantum Number (ml)

The magnetic quantum number, ml, to represent the orbitals that a offered subshell. Because that a given l, ml can variety from -l come +l. A ns subshell (l=1), for instance, have the right to have three orbitals matching to ml = -1, 0, +1. In various other words, it defines the px, py and pzorbitals that the ns subshell. (However, the ml number don"t necessarily exchange mail to a given orbital. The truth that there room three orbitals merely is indicative the the 3 orbitals that a ns subshell.) In general, because that a provided l, there are 2l+1 possible values for ml; and in a n major shell, there room n2 orbitals discovered in that energy level.

Continuing on indigenous out example from above, the ml worths of Iodine room ml = -4, -3, -2, -1, 0 1, 2, 3, 4. This arbitrarily exchange mail to the 5s, 5px, 5py, 5pz, 4dx2-y2, 4dz2, 4dxy, 4dxz, and 4dyz orbitals.

Spin Magnetic Quantum Number (ms)

The rotate magnetic quantum number can only have actually a value of one of two people +1/2 or -1/2. The worth of 1/2 is the turn quantum number, s, which describes the electron"s spin. Because of the turn of the electron, the generates a magnetic field. In general, an electron v a ms=+1/2 is called ­­an alpha electron, and also 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 the these 4 quantum numbers, however, Bohr postulated that only the major quantum number, n, identify the power of the electron. Therefore, the 3s orbit (l=0) has actually the same power as the 3p (l=1) and also 3d (l=2) orbitals, regardless of a difference in l values. This postulate, however, hold true only for Bohr"s hydrogen atom or various other hydrogen-like atoms.

When handling multi-electron systems, we must take into consideration the electron-electron interactions. Hence, the previously defined postulate breaks down in the the power of the electron is now figured out by both the major quantum number, n, and the orbit angular inert quantum number, l. Although the Schrodinger equation for many-electron atom is extremely an overwhelming to fix mathematically, we deserve to still define their digital structures via electron configurations.

General rule of Electron Configuration

There space a set of basic rules the are provided to number out the electron construction of an atomic species: Aufbau Principle, Hund"s Rule and the Pauli-Exclusion Principle. Before continuing, it"s crucial to know that every orbital can be inhabited by two electrons of opposite spin (which will be further questioned later). The complying with table reflects the possible number of electrons that deserve to occupy every orbital in a given 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 check out on the regular table that its atomic number is 53 (meaning it includes 53 electrons in its neutral state). Its finish electron construction is 1s22s22p63s23p64s23d104p65s24d105p5. If you counting up all of these electrons, you will view that it adds approximately 53 electrons. Notification that every subshell have the right to only contain the max amount of electrons as indicated in the table above.

Aufbau Principle

The indigenous "Aufbau" is German for "building up". The Aufbau Principle, also called the building-up principle, states that electron"s occupy orbitals in bespeak of increasing energy. The bespeak of occupation is together follows:



Hund"s dominion states that when electrons occupy degenerate orbitals (i.e. Very same n and l quantum numbers), they must an initial occupy the north orbitals before double occupying them. Furthermore, the most stable configuration results when the spins room parallel (i.e. Every alpha electrons or all beta electrons). Nitrogen, for example, has actually 3 electron occupying the 2p orbital. According to Hund"s Rule, lock must very first occupy each of the three degenerate p orbitals, specific the 2px orbital, 2py orbital, and the 2pz orbital, and also with parallel spins (Figure 2). The configuration listed below is incorrect due to the fact that the 3rd electron rectal does no occupy the empty 2pz orbital. Instead, it occupies the half-filled 2px orbital. This, therefore, is a violation of Hund"s dominion (Figure 2).

Figure 2. A visual representation of the Aufbau Principle and also Hund"s Rule. Note that the pour it until it is full of electron in every orbital(px, py and also pz) is arbitrary as lengthy as the electrons room singly filled before having two electrons accounting the exact same orbital.(a)This diagram represents the correct filling the electrons because that the nitrogen atom. (b) This diagramrepresents the incorrectfilling the the electrons for the nitrogen atom.

Electronic configuration of Cations and Anions

The method we designate digital configurations because that cations and also anions is essentially comparable to the for neutral atoms in their ground state. That is, us follow the three essential rules: Aufbau Principle, Pauli-exclusion Principle, and also Hund"s Rule. The digital configuration the cations is assigned by removing electrons first in the outermost ns orbital, adhered to by the s orbital and finally the d orbitals (if any more electrons should be removed). Because that instance, the floor state digital configuration the calcium (Z=20) is 1s22s22p63s23p64s2. The calcium ion (Ca2+), however, has actually two electrons less. Hence, the electron construction for Ca2+ is 1s22s22p63s23p6. Because we should take away 2 electrons, we an initial remove electron from the outermost covering (n=4). In this case, every the 4p subshells space empty; hence, we start by removing native the s orbital, i m sorry is the 4s orbital. The electron construction for Ca2+ is the very same as that for Argon, which has actually 18 electrons. Hence, we can say that both room isoelectronic.

The electronic configuration that anions is assigned by adding electrons according to Aufbau Principle. We include electrons to to fill the outermost orbital the is occupied, and also then add an ext electrons to the next greater orbital. The neutral atom chlorine (Z=17), because that instance has actually 17 electrons. Therefore, its floor state electronic configuration can be written as 1s22s22p63s23p5. The chloride ion (Cl-), on the other hand, has second electron because that a total of 18 electrons. Adhering to Aufbau Principle, the electron occupies the partially filled 3p subshell first, do the 3p orbital totally filled. The electronic configuration for Cl- can, therefore, it is in designated together 1s22s22p63s23p6. Again, the electron construction for the chloride ion is the same as the for Ca2+ and Argon. Hence, they are all isoelectronic to every other.


1. I m sorry of the princples explained above tells us that electrons that are paired cannot have the exact same spin value?

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

a. Mg

b. Ga

c. Co

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

4. Which of the adhering to 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. Write 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 have the right 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 deserve to be one of two people +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; ms = +1/2. Osmium (Os) is one example.

4. A. The value of l can not be 4, due to the fact that l ranges from (0 - n-1)

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

c. Okay

d. Okay

e. The worth of n can not be zero.

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5. A. 1s22s22p63s23p3

b. 1s22s22p63s23p6

c. 1s22s22p63s23p64s23d7


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