The electron configuration of periodic elements
Electron configuration holds the key to the chemical world. Our present-day understanding of the chemical properties of inorganic and organic compounds based on the electronic configuration of the constituent elements.
In multi-electron atoms, experimental studies of 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.
Rules for writing electronic configuration
The electron configuration of elements or its ions takes place according to the following rules
- 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 and 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.
Electron configuration and energy levels
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 orbitals originating from the same principal quantum number n 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.
According to this diagram, the energy levels are
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’s 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.
Periodic table and electronic configuration
Extranuclear electrons are responsible for the chemical behavior of elements and periodic classification of the elements also based on the chemical behavior.
Thus the electronic configuration of elements must be connected with the periodic table. Especially, the arrangement of the electrons in the outermost orbitals detects the position of the elements in the periodic table.
S block electron 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 electron configuration
Electronic structure 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 structure 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 outer electronic configuration of the p-block element is
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
The first metal in the first transition series starts with scandium and ending with zinc.
Thus the twenty-first electron goes to the next available higher energy 3d orbital and five 3d subshells with the capacity of ten electrons. So 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|
Experimental studies on Cr and Cu revel 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.