The **electron configuration** of one atomic species (neutral or ionic) allows us to recognize the shape and energy that its electrons. Countless general rules are taken into factor to consider when assigning the "location" that the electron to its prospective power state, yet these assignments are arbitrary and it is constantly uncertain as to which electron is being described. Understanding the electron configuration of a species gives united state a far better understanding of its bonding ability, magnetism and also other starrkingschool.netical properties.

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## Introduction

The **electron configuration** is the typical notation used to define the digital structure of an atom. Under the orbit approximation, we let each electron accounting an orbital, which can be resolved by a solitary wavefunction. In act so, we attain three quantum numbers (n,*l*,ml), which room the same as the ones derived from resolving the Schrodinger"s equation for Bohr"s hydrogen atom. Hence, countless of the rules that we usage to define the electron"s deal with in the hydrogen atom can likewise be supplied in systems including multiple electrons. As soon as 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 systems to the Schrödinger equation. By addressing the Schrödinger equation for the hydrogen atom, we acquire three quantum numbers, namely the major quantum number (n), the orbit angular momentum quantum number (*l*), and the magnetic quantum number (ml). There is a fourth quantum number, referred to as the spin magnetic quantum number (ms), which is not obtained from fixing the Schrödinger equation. Together, these four quantum numbers deserve to be provided to define the location of one electron in Bohr"s hydrogen atom. This numbers deserve to be believed of together an electron"s "address" in the atom.

## Notation

To assist describe the appropriate notation for electron configuration, the is finest to do so v example. Because that this example, us will usage the iodine atom. There space two means in which electron configuration have the right to be written:

I: 1s22s22p63s23p64s23d104p65s24d105p5

or

I:

In both of these varieties of notations, the order of the energy levels should be written by boosted energy, reflecting the number of electrons in each subshell as an exponent. In the quick notation, you location brackets roughly the *preceding* noble gas element followed by the valence covering electron configuration. The regular table shows that kyrpton (Kr) is the previous noble gas listed before iodine. The noble gas construction encompases the energy states reduced than the valence covering electrons. Therefore, in this instance

### Principal Quantum Number (n)

The major quantum number *n* suggests the shell or power level in which 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 one electron. This quantum number have the right to only be positive, non-zero, and integer values. The is, *n*=1,2,3,4,..

For example, one Iodine atom has its outmost electron 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*, shows the subshell the the electron. Girlfriend can additionally tell the shape of the atomic 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 it is in positive and integer values, return it have the right to take ~ above a zero value. In general, for every worth of n, there room n worths of *l*. Furthermore, the worth of *l* varieties from 0 come n-1. Because that example, if n=3, *l*=0,1,2.

So in regards come the instance used above, the *l *values of Iodine because that 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 selection from *-l* to *+l*. A p subshell (*l*=1), for instance, deserve to have three orbitals matching to ml = -1, 0, +1. In other words, it defines the px, py and pzorbitals of the p subshell. (However, the ml number don"t necessarily correspond to a offered orbital. The fact that there space three orbitals just is indicative of the three orbitals that a p subshell.) In general, for a provided *l*, there are 2*l*+1 possible values because that ml; and in a *n* principal shell, there space *n*2 orbitals found in that energy level.

Continuing on indigenous out example from above, the ml values of Iodine space 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 also 4dyz orbitals.

### Spin Magnetic Quantum Number (ms)

The rotate magnetic quantum number deserve to only have actually a worth of either +1/2 or -1/2. The worth of 1/2 is the spin quantum number, s, which explains the electron"s spin. Due to the turn of the electron, it generates a magnetic field. In general, one electron through a ms=+1/2 is referred to as an alpha electron, and also one with a ms=-1/2 is called a beta electron. No two paired electrons can have the exact same spin value.

Out the these four quantum numbers, however, Bohr postulated that only the principal quantum number, n, identify the energy of the electron. Therefore, the 3s orbit (*l*=0) has actually the same power 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 managing multi-electron systems, we must take into consideration the electron-electron interactions. Hence, the previously described postulate breaks down in the the power of the electron is now established by both the major quantum number, n, and the orbit angular inert quantum number, *l*. Return the Schrodinger equation for many-electron atoms is extremely difficult to settle mathematically, we can still describe their electronic structures via electron configurations.

## General rules of Electron Configuration

There space a set of basic rules the are supplied to number out the electron configuration of an atomic species: Aufbau Principle, Hund"s Rule and the Pauli-Exclusion Principle. Before continuing, it"s necessary to recognize that each orbital have the right to be occupied by *two* electron of opposite turn (which will be further disputed later). The adhering to table mirrors the *possible* variety of electrons that deserve to occupy every 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) | 14 |

Using our example, iodine, again, we check out on the periodic table the its atom number is 53 (meaning it consists of 53 electrons in that is neutral state). Its complete electron configuration is 1s22s22p63s23p64s23d104p65s24d105p5. If you count up all of these electrons, friend will watch that the adds up to 53 electrons. An alert that every subshell have the right to only save the max lot of electrons 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, states that electron"s accounting orbitals in order of increasing energy. The stimulate of occupation is together follows:

**1s**

**Hund"s dominion states that as soon as electrons accounting degenerate orbitals (i.e. Exact same n and also l quantum numbers), lock must first occupy the empty orbitals before double occupying them. Furthermore, the many stable configuration results as soon as the spins space parallel (i.e. All alpha electrons or every beta electrons). Nitrogen, for example, has 3 electron occupying the 2p orbital. Follow to Hund"s Rule, lock must very first occupy each of the 3 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 3rd electron occupies does not occupy the empty 2pz orbital. Instead, it rectal the half-filled 2px orbital. This, therefore, is a violation the Hund"s rule (Figure 2).**

**Figure 2. A visual representation of the Aufbau Principle and also Hund"s Rule. Note that the filling of electrons in every orbital(px, py and pz) is arbitrarily as long as the electrons are singly filled prior to having two electrons accounting the same orbital.(a)This diagram represents the**

*correct*filling that electrons because that the nitrogen atom. (b) This diagramrepresents the*incorrect*filling the the electrons because that the nitrogen atom.## Electronic construction of Cations and Anions

The means we designate electronic configurations because that cations and also anions is essentially similar to the for neutral atoms in your ground state. The is, we follow the three crucial rules: Aufbau Principle, Pauli-exclusion Principle, and Hund"s Rule. The electronic configuration of cations is assigned by removing electrons very first in the outermost ns orbital, adhered to by the s orbital and finally the d orbitals (if any more electrons have to be removed). For instance, the floor state electronic configuration of calcium (Z=20) is 1s22s22p63s23p64s2. The calcium ion (Ca2+), however, has actually two electrons less. Hence, the electron configuration for Ca2+ is 1s22s22p63s23p6. Since we should take away two electrons, we an initial remove electron from the outermost shell (n=4). In this case, all the 4p subshells room empty; hence, we begin by removing from the s orbital, which is the 4s orbital. The electron configuration for Ca2+ is the same as that for Argon, which has 18 electrons. Hence, we have the right to say the both are isoelectronic.

The digital configuration that anions is assigned by adding electrons according to Aufbau Principle. We include electrons to fill the outermost orbital that is occupied, and also then add more electrons come the next higher orbital. The neutral atom chlorine (Z=17), because that instance has actually 17 electrons. Therefore, its ground state digital configuration deserve to be composed as 1s22s22p63s23p5. The chloride ion (Cl-), ~ above the other hand, has secondary electron because that a total of 18 electrons. Complying with Aufbau Principle, the electron rectal the partly filled 3p subshell first, make the 3p orbital completely filled. The electronic configuration for Cl- can, therefore, be designated together 1s22s22p63s23p6. Again, the electron configuration for the chloride ion is the exact same as the for Ca2+ and also Argon. Hence, they space all isoelectronic to each other.

## Problems

1. I m sorry of the princples explained above tells united state that electrons that are paired cannot have actually the very same spin value?

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

a. Mg

b. Ga

c. Co

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

4. I m sorry of the adhering to cannot exist (there may be 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; ms = +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+

## Answers

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 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 have the right to be either +1/2 or -1/2

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

4. A. The value of *l* can not be 4, due to the fact that *l* arrays 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

## References

Atkins, P. W., & De Paula, J. (2006).*Physical starrkingschool.netistry for the Life Sciences.*brand-new York, NY: W. H. Freeman and Company. Petrucci, R. H., Harwood, W. S., & Herring, F. G. (2002).*General starrkingschool.netistry: ethics and contemporary Applications.*top Saddle River, NJ: Prentice-Hall, Inc. Shagoury, Richard.*starrkingschool.netistry 1A lecture Book.*4th Ed. Practice Publishing. 2006. Print