Electronic configuration formula
The electron configuration of elements holds the key to the chemical world. Hence electronic configuration formula is an essential tool to predict the chemical properties of elements. Therefore to find the electron configuration first we remember the energy of orbitals.
Periodic table classification based on the electron configuration reflects the electronic structure of elements. Thus for s, p, d, and f block elements have outermost orbitals with s, p, d, and f orbitals.
Energy of electron in orbitals
The atomic spectra show that orbitals with the same value of principal quantum numbers have different values of azimuthal quantum numbers. Thus these quantum levels are different energy values.
3S orbital lower energy than 3P orbitals which again lower energy than 3d orbitals. But the orbitals belonging to a particular type ( P or d or f ) will be of the equal energy of an atom or an ion.
Formula to find electron configuration
To find the electron configuration of elements or its ions takes place according to the following formula
- The maximum number of electrons in the main quantum shell = 2n2. Where n = principal quantum number.
- Again we see that the principal quantum shell divided into sub shell s, p, d, f, the maximum capacity of electrons in a subshell = 2(2l +1).
Where l = 0, 1, 2, 3 for s, p, d, f orbitals respectively.
- Aufbau building up principle provides the electron filling up process. Hence according to this principle, the orbitals are filled up in the order of increasing energy of an electron. Thus orbitals with the lowest energy filled up first while the highest energy orbital filled up in the end.
- Electrons will tend to maintain maximum spin. Thus electrons with similar spin occupied first will prefer to remain unpaired.
- According to Hund’s rule, electrons are filling in the orbital with maximum spin multiplicity.
- Spin pairing occurs only when vacant orbitals of similar energy are not available for occupation.
Energy levels of electron orbitals
It is difficult for the readers to remember the orbital energy diagram for many-electrons atoms. Thus a trivial way to remember these energy levels provides below this diagram
- The different electron orbitals originating from the same energy levels are written in the horizontal lines.
- Now inclined parallel lines are drawn through the orbitals according to the above picture. Filling up the different orbitals by electrons will follow these lines.
Therefore according to above diagram, the energy levels of electrons orbitals
1S < 2S < 2P < 3S < 3P < 4S < 3d < 4P < 5S < 4d < 5P < 6S < 4f < 5d < 6P < 7S < 5f…
Pauli exclusion principle
Pauli exclusion principle uses for the pictorial representation of electron configuration.
No two electrons of the atom can have the same four quantum numbers.
An alternative statement of Pauli exclusion principle, no more than two electrons can be placed in one and the same orbital.
When an orbital contains two electrons, the electrons are paired. These two electrons per orbital given the maximum accommodation of electrons.
Electron configuration and the periodic table
Extranuclear electrons are responsible for the chemical bonding of elements and periodic table classification of the elements also based on the chemical behavior.
Thus the electronic configuration formula of elements must be connected with the periodic table. Especially, the arrangement of the electron in the outermost energy levels of orbitals detects the position of the elements in the periodic table.
S block electronic configuration
Group 1 and 2 belong to s-block elements in the periodic table with one or two-electron or electrons in outermost s orbital. Thus the general electronic configuration of s-block elements
Electronic configuration of group 1 elements
|3||Lithium (Li)||1S2 2S1|
|11||Sodium (Na)||[Ne] 3S1|
|19||Potassium (K)||[Ar] 4S1|
|37||Rubidium (Rb)||[Kr] 5S1|
|55||Cesium (Cs)||[Xe] 3S1|
|87||Francium (Fr)||[Rn] 3S1|
Electronic configuration of group 2 elements
|4||Beryllium (Be)||1S2 2S2|
|20||Calcium (K)||[Ar] 4S2|
|38||Strontium (Sr)||[Kr] 5S2|
|56||Barium (Ba)||[Xe] 6S2|
|88||Radium (Ra)||[Rn] 7S2|
Electronic configuration of the P block
P block constructed by six groups from the group-13 to group-18 and from period 2 to period 6 with valence shell configuration nP1 to nP6 in the periodic table. Thus the general formula to find the outer electron configuration of the p-block element in the periodic table
Electronic configuration of group 13 elements
|13||Aluminum (Al)||[Ne] 3S23P1|
|31||Galium (Ga)||[Ar] 4S24P1|
|49||Indium (In)||[Kr] 5S25P1|
|81||Thallium (Tl)||[Xe] 6S26P1|
Electronic configuration of group 14 elements
|14||Silicon (Si)||[Ne] 3S23P2|
|32||Germanium (Ge)||[Ar] 4S24P2|
|50||Tin (Sn)||[Kr] 5S25P2|
|82||Lead (Pb)||[Xe] 6S26P2|
Electronic configuration of group 15 elements
|15||Phosphorus (P)||[Ne] 3S23P3|
|33||Arsenic (Ge)||[Ar] 4S24P3|
|51||Antimony (Sn)||[Kr] 5S25P3|
|83||Bismuth (Pb)||[Xe] 6S26P3|
Electronic configuration of group 16 elements
|16||Sulfur (S)||[Ne] 3S23P4|
|34||Selenium (Se)||[Ar] 4S24P4|
|52||Tellurium (Te)||[Kr] 5S25P4|
|84||Polonium (Po)||[Xe] 6S26P4|
Electronic configuration of group 17 elements
|17||Chlorine (Cl)||[Ne] 3S23P5|
|35||Bromine (Br)||[Ar] 4S24P5|
|53||Iodine (I)||[Kr] 5S25P5|
|85||Austin (At)||[Xe] 6S26P5|
Electronic configuration of noble gases
|18||Argon (Ar)||[Ne] 3S23P6|
|36||Krypton (Kr)||[Ar] 4S24P6|
|54||Xenon (Xe)||[Kr] 5S25P6|
|86||Radon (Rn)||[Xe] 6S26P6|
d-block electron configuration examples
The first metal in the first transition series starts with scandium and ending with zinc.
When the twenty-first electron goes to the next available higher energy 3d orbital and five 3d subshells with the capacity of ten electrons. Therefore the general electron configuration of 3d block elements are
[Ar] 4S1→2 3d1→10
Electronic configuration of 3d series
|Scandium (Sc)||[Ar] 4S2 3d1|
|Titanium (Ti)||[Ar] 4S2 3d2|
|Vanadium (V)||[Ar] 4S2 3d3|
|Chromium (Cr)||[Ar] 4S1 3d5|
|Manganese (Mn)||[Ar] 4S2 3d5|
|Iron (Fe)||[Ar] 4S2 3d6|
|Cobalt (Co)||[Ar] 4S2 3d7|
|Nickel (Ni)||[Kr] 4S2 3d8|
|Copper (Cu)||[Ar] 4S1 3d10|
|Zinc (Zn)||[Ar] 4S2 3d10|
A study on Cr and Cu reveals their general electron configuration trends. The general electron configuration of Cr and Cu are
Cr: [Ar]4S2 3d4
Cu: [Ar] 4S2 3d9
But half-filled or filled orbital is relatively more stable than the partially filled orbital. Thus Cr and Cu reordering its electrons to gain extra stability associated with a half-filled or filled d subshell.