Quantum NumbersGeneral rules of Electron configuration

The electron configuration of an atomic types (neutral or ionic) enables us to recognize the shape and energy that its electrons. Numerous general rules space taken into consideration when assigning the "location" of the electron come its prospective power state, yet these assignments room arbitrary and it is always uncertain regarding which electron is being described. Knowing the electron construction of a types gives us a much better understanding of its bonding ability, magnetism and other keolistravelservices.comical properties.

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The electron configuration is the conventional notation offered to explain the electronic structure of one atom. Under the orbital approximation, us let every electron occupy an orbital, which have the right to be resolved by a single wavefunction. In act so, we attain three quantum numbers (n,l,ml), which space the exact same as the ones obtained from addressing the Schrodinger"s equation because that Bohr"s hydrogen atom. Hence, countless of the rules the we use to define the electron"s deal with in the hydrogen atom can also be supplied in systems entailing multiple electrons. When assigning electrons to orbitals, we must follow a collection of 3 rules: the Aufbau Principle, the Pauli-Exclusion Principle, and also Hund"s Rule.

The wavefunction is the systems to the Schrödinger equation. By addressing the Schrödinger equation because that the hydrogen atom, we achieve three quantum numbers, namely the principal quantum number (n), the orbital angular momentum quantum number (l), and also the magnetic quantum number (ml). There is a fourth quantum number, dubbed the rotate magnetic quantum number (ms), i beg your pardon is not acquired from addressing the Schrödinger equation. Together, these 4 quantum numbers can be provided to explain the ar of one electron in Bohr"s hydrogen atom. These numbers deserve to be assumed of together an electron"s "address" in the atom.


To aid describe the proper notation because that electron configuration, that is ideal to carry out so with example. For this example, we will use the iodine atom. There space two means in which electron configuration have the right to be written:

I: 1s22s22p63s23p64s23d104p65s24d105p5


I: 5s24d105p5

In both that these types of notations, the bespeak of the energy levels need to be written by increased energy, mirroring the variety of electrons in every subshell as an exponent. In the brief notation, you location brackets roughly the preceding noble gas facet followed by the valence covering electron configuration. The regular table reflects that kyrpton (Kr) is the vault noble gas detailed before iodine. The noble gas construction encompases the power states reduced than the valence covering electrons. Therefore, in this instance =1s22s22p63s23p64s23d104p6.

Principal Quantum Number (n)

The principal quantum number n indicates the shell or power level in i beg your pardon the electron is found. The value of n have the right to be set between 1 come n, wherein n is the value of the outermost shell containing an electron. This quantum number deserve to only be positive, non-zero, and also integer values. The is, n=1,2,3,4,..

For example, one Iodine atom has actually its outmost electrons in the 5p orbital. Therefore, the principle quantum number because that Iodine is 5.

Orbital Angular momentum Quantum Number (l)

The orbit angular inert quantum number, l, indicates the subshell of the electron. Friend can additionally tell the shape of the atom orbital with this quantum number. An s subshell coincides to l=0, a p subshell = 1, a d subshell = 2, a f subshell = 3, and so forth. This quantum number can only it is in 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 come n-1. Because that 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 of a offered subshell. Because that a offered l, ml can variety from -l to +l. A p subshell (l=1), because that instance, can have three orbitals equivalent to ml = -1, 0, +1. In other words, it specifies the px, py and also pzorbitals that the p subshell. (However, the ml numbers don"t necessarily exchange mail to a offered orbital. The fact that there are three orbitals merely is indicative the the three orbitals of a p subshell.) In general, because that a offered l, there room 2l+1 possible values because that ml; and in a n principal shell, there room n2 orbitals discovered in that energy level.

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

Spin Magnetic Quantum Number (ms)

The spin magnetic quantum number have the right to only have a worth of one of two people +1/2 or -1/2. The worth of 1/2 is the rotate quantum number, s, which defines the electron"s spin. As result of the rotate of the electron, it generates a magnetic field. In general, one electron with a ms=+1/2 is dubbed ­­an alpha electron, and also one through a ­ms=-1/2 is referred to as a beta electron. No 2 paired electrons deserve to have the exact same spin value.

Out the these 4 quantum numbers, however, Bohr postulated that just the primary quantum number, n, determines the energy of the electron. Therefore, the 3s orbital (l=0) has actually the same power as the 3p (l=1) and also 3d (l=2) orbitals, regardless of a distinction in l values. This postulate, however, stop true just for Bohr"s hydrogen atom or other hydrogen-like atoms.

When dealing with multi-electron systems, we must consider the electron-electron interactions. Hence, the previously described postulate breaks under in the the energy of the electron is now determined by both the principal quantum number, n, and the orbit angular momentum quantum number, l. Although the Schrodinger equation for many-electron atom is extremely an overwhelming to deal with mathematically, we have the right to still explain their electronic structures via electron configurations.

General rules of Electron Configuration

There are a set of general rules that are used to number out the electron configuration of an atomic species: Aufbau Principle, Hund"s Rule and the Pauli-Exclusion Principle. Prior to continuing, it"s essential to know that every orbital have the right to be populated by two electrons of opposite rotate (which will be further debated later). The following table reflects the possible variety of electrons that have the right to occupy each orbital in a offered subshell.

subshell number of orbitals total variety of possible electrons in every 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 view on the periodic table the its atomic number is 53 (meaning it has 53 electrons in that is neutral state). Its finish electron configuration is 1s22s22p63s23p64s23d104p65s24d105p5. If you count up every one of these electrons, friend will check out that that adds up to 53 electrons. Notice that every subshell have the right to only contain the max quantity of electron as indicated in the table above.

Aufbau Principle

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



Hund"s dominance states that as soon as electrons occupy degenerate orbitals (i.e. Exact same n and also l quantum numbers), they must first occupy the empty orbitals before dual occupying them. Furthermore, the many stable configuration results once the spins room parallel (i.e. Every alpha electrons or every beta electrons). Nitrogen, for example, has actually 3 electrons occupying the 2p orbital. Follow to Hund"s Rule, lock must an initial occupy every of the three degenerate ns orbitals, specific the 2px orbital, 2py orbital, and also the 2pz orbital, and with parallel spins (Figure 2). The configuration below is incorrect because the third electron occupies does no occupy the north 2pz orbital. Instead, it rectal the half-filled 2px orbital. This, therefore, is a violation of Hund"s dominion (Figure 2).

Figure 2. A visual depiction of the Aufbau Principle and also Hund"s Rule. Note that the filling of electrons in each orbital(px, py and pz) is arbitrarily as long as the electrons are singly filled prior to having 2 electrons accounting the exact same orbital.(a)This diagram to represent the correct filling that electrons because that the nitrogen atom. (b) This diagramrepresents the incorrectfilling the the electrons because that the nitrogen atom.

Electronic configuration of Cations and also Anions

The means we designate electronic configurations because that cations and also anions is essentially comparable to the for neutral atom in your ground state. That is, we follow the three crucial rules: Aufbau Principle, Pauli-exclusion Principle, and also Hund"s Rule. The digital configuration that cations is assigned by removed electrons first in the outermost ns orbital, followed by the s orbital and finally the d orbitals (if any much more electrons need to be removed). For instance, the ground state digital configuration of calcium (Z=20) is 1s22s22p63s23p64s2. The calcium ion (Ca2+), however, has two electron less. Hence, the electron construction for Ca2+ is 1s22s22p63s23p6. Since we need to take away two electrons, we very first remove electron from the outermost covering (n=4). In this case, every the 4p subshells are empty; hence, we begin by removing indigenous the s orbital, i beg your pardon is the 4s orbital. The electron configuration for Ca2+ is the very same as the for Argon, which has actually 18 electrons. Hence, we deserve to say the 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 that is occupied, and also then add an ext electrons to the next higher orbital. The neutral atom chlorine (Z=17), for instance has actually 17 electrons. Therefore, its ground state digital configuration have the right to be written as 1s22s22p63s23p5. The chloride ion (Cl-), on the various other hand, has an additional electron because that a complete of 18 electrons. Complying with Aufbau Principle, the electron occupies the partially filled 3p subshell first, make the 3p orbital fully filled. The digital configuration because that Cl- can, therefore, it is in designated as 1s22s22p63s23p6. Again, the electron construction for the chloride ion is the very same as that for Ca2+ and Argon. Hence, they room all isoelectronic to every other.


1. I beg your pardon of the princples explained over tells us that electron that space paired cannot have the same spin value?

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

a. Mg

b. Ga

c. Co

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

4. Which of the adhering to cannot exist (there might be much more than one answer):

a. N = 4; l = 4; ml = -2; ms = +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 for 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 either +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 one of two people +1/2 or -1/2

c. N = 3; l = 0, 1, 2; ml = -2, -1, 0, 1, 2, 3; ms can 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 can not be 4, due to the fact that l arrays from (0 - n-1)

b. Ms have the right to only it is in +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 keolistravelservices.comistry for the Life Sciences. brand-new York, NY: W. H. Freeman and also Company. Petrucci, R. H., Harwood, W. S., & Herring, F. G. (2002). General keolistravelservices.comistry: ethics and contemporary Applications. top Saddle River, NJ: Prentice-Hall, Inc. Shagoury, Richard. keolistravelservices.comistry 1A class Book. 4th Ed. Custom Publishing. 2006. Print