What Is A Periodic Table And Electronic Configuration
Periodic Table is the positioning or an arrangement of every known element in the earth based on periodic law, the elements are arranged in such a manner that the elements having similar properties are placed on the same vertical column.
All the elements in the periodic table are displayed from top to bottom and left to right in accordance with their increasing atomic number. As a result, the periodic table exhibit some characters with are as follows:
● All the elements in the same group (vertical column of a periodic table) tend to possess the same valence electronic configuration as a result they exhibit common properties.
● All the elements in the same period (horizontal row of a periodic table) tend to show the character of increase in the number of valence electrons as we move forward from the beginning of a particular period.
The naturally occurring elements of the periodic table are the first 94 elements and the rest of the elements from 95 to 118 have been synthesized artificially by the scientists.
The representation in which the electrons of an element are distributed in its atomic shell is called electronic configuration. The electronic configuration of an element is depicted with certain standard notations which contain all the atomic subshells with their number of electrons written in superscript. Sometimes the standard abbreviation becomes very lengthy so to reduce the length the sequence of subshells which are completely filled is replaced with a noble gas symbol in brackets which is having the same electronic configuration as the completely filled subshell. Example [Ne] 3s2 is the abbreviated standard of Mg.
Electronic configuration is useful in the following ways: -
● Elements which have similar electronic configuration exhibit similar properties.
● It can be used to interpret the atomic spectra.
● Valency of an electron can be determined.
Exceptions Of Electronic Configuration In Periodic Table
There are many exceptions present in the periodic table, the exception is mainly due to the different electronic configuration exhibited by the elements. According to the Aufbau Principle, in the ground state of an ion or atom, the subshells are filled from the lower energy levels to higher energy levels in an increasing order and the Hund’s Rule of Maximum Multiplicity states that when the orbitals start getting filled the electrons tends to remain unpaired as far as possible and have the same direction of spin. But these rules get violated in some cases.
The two main exceptions of the d-block are chromium and copper. The reason for the exception is that the completely filled subshells or the half-filled subshell have extra stability. As a result, the type p3, d5, f7 (half-filled) or p6, d10, f14 (completely-filled) poses more stability. In the case of chromium (Cr) we witness this concept of extra stability of half- filled subshells, here we can see that in chromium (Cr) the configuration should be [Ar] 3d4 4s2 but the actual configuration is [Ar] 3d5 4s1. This makes the subshells d and s both half-filled and provides an extra stability. Similarly in the case of copper (Cu) the electronic configuration should be [Kr] 3d9 4s2 but the actual configuration is [Kr] 3d10 4s1. This makes the d shell completely filled and the s shell half-filled imparting more stability. Molybdenum (Mo) and silver (Ag) follow similar behavior and fall under the category of expectation.
In p-block there is only one expectation which is helium (He) which has configuration of 1s2 and the element has no resemblance of its group i.e., other members of the noble gas group have a configuration of ns2 np6.
In the f-block, the elements which possess exceptional electron configurations are La, Ce and Ge in the lanthanide series and Ac,Th, Pa, U, Np and Cm in the actinide series. All the mentioned elements resemble Aufbau exceptions.
Electronic Configuration The Bedrock Of The Periodic Table
Electronic configuration of an element is unique because each element has its own atomic number. Atomic number is the number of protons present in an electrically neutral element or the number of electrons present in an electrically neutral element. Electronic configuration can be used to describe the orbital of an atom when the element is in ground state or in an ionized state whether it be a cation or an anion. Moreover, with the electronic configuration we can represent exactly in which orbital of which subshell an electron is more or missing when the element is in ionized form. There are in total 4 types of orbitals s, p, d and f. Each type of orbital has a different structure but they can hold a maximum of 2 electrons in each orbital like p has different orbitals of px, py and pz. Same orbitals have similar structure but have different energy levels like 3dxy and 4dxy have the same characteristics (spherical volume probability, radial node etc.) but they inhibit different spaces around the nucleus. The chemical and physical properties of an element can be correlated with its unique electronic configuration.
We find that in the periodic table the elements in the same group have the same properties because all the elements in a group have the same valence electronic configuration. According to the modern periodic table, the chemical and physical properties are the periodic functions of their atomic number.
Periodic table is nothing but an organized way in which all the existing elements are represented in a tabular form. It is arranged in the order of increasing atomic number and subsequently on the basis of electronic configuration because it is the electronic configuration only which can predict the similarity between two elements or more elements.
How Do You Find An Electronic Configuration Using The Periodic Table
As the periodic table is made on the basis of electronic configuration it becomes much easier to find out the electronic configuration of an element. While finding the configuration we have to follow the following steps: -
● First, we must identify the element of which we want to find the electronic configuration.
● After identifying the element, we must track on which period the element belongs to, it means we have to find out on which shell the element belongs. Period is the energy level or shell i.e., for n= 3 shells there will be one 3s orbital, three 3p orbital and five 3d orbital.
● Then we must find on which block the element belongs to if it is on s-block then the last subshell will be s only and if it is on the p-block then the last subshell of the electronic configuration will be p.
● When we have found out the period and block of the element we can easily come up with the electronic configuration after knowing the atomic number, which can be easily done by moving backward from the current position of the element till we reach a noble gas.
General outer electronic configuration of the s-block elements is of type ns1-2.
General outer electronic configuration of the p-block elements is of type ns2 np1-6.
General outer electronic configuration of the d-block elements is of type (n - 1) d1-10 ns1-2.
General outer electronic configuration of the f-block elements is of type (n - 2) f1-14 (n-1) d0-1 ns2.
How Many Elements In The Modern Periodic Table Shows Exceptional Ground State Electronic Configuration
The elements of period 4 and 5 which exhibits exceptional electronic configuration in ground state are chromium ([Ar] 3d5 4s1), niobium ([Kr] 5s1 4d4), copper ([Ar] 3d10 4s1), molybdenum ([Kr]5s1 4d5), ruthenium ([Kr] 5s1 4d7), rhodium ([Kr] 5s1 4d8), palladium ([Kr] 4d10), silver ([Kr]5s1 4d10).
The elements of period 6 and 7 which exhibits exceptional electronic configuration in ground state are lanthanum ([Xe] 6s2 5d1), actinium ([Xe] 7s2 6d1), cerium ([Xe] 6s2 4f1 5d1), thorium ([Xe] 7s2 6d2), gadolinium ([Xe] 6s2 4f7 5d1), protactinium ([Xe] 7s2 5f2 6d1), platinum ( [Xe] 6s1 4f14 5d9), uranium ([Rd] 7s2 5f3 6d1), gold ([Rn] 6s1 4f14 5d10), neptunium ([Rn] 7s2 5f4 6d1), curium ([Rn] 7s2 5f7 6d1), lawrencium ([Rn] 7s2 5f14 7p1).
