- and f - inner transition series of elements are placed separately in the Periodic Table to maintain its structure and to preserve the principle of classification by keeping elements with similar properties in a single column. Problem . How would you justify the presence of elements in the th period of the Periodic Table? When n = , l = , , , .
The order in which the energy of the available orbitals d , s and p increases is s < d < p . The total number of orbitals available are . The maximum number of electrons that can be accommodated is ; and therefore elements are there in the th period. (b) Groupwise Electronic Configurations Elements in the same vertical column or group have similar valence shell electronic configurations, the same number of electrons in the outer orbitals, and similar properties.
For example, the Group elements (alkali metals) all have ns valence shell electronic configuration as shown below. a theoretical foundation for the periodic classification. The elements in a vertical column of the Periodic Table constitute a group or family and exhibit similar chemical behaviour. This similarity arises because these elements have the same number and same distribution of electrons in their outermost orbitals.
We can classify the elements into four blocks viz ., s -block, p -block, d -block and f -block depending on the type of atomic orbitals that are being filled with electrons. This is illustrated in Fig. . .
We notice two exceptions to this categorisation. Strictly, helium belongs to the s -block but its positioning in the p -block along with other group elements is justified because it has a completely filled valence shell ( s ) and as a result, exhibits properties characteristic of other noble gases. The other exception is hydrogen. It has only one s -electron and hence can be placed in group (alkali metals).
It can also gain an electron to achieve a noble gas arrangement and hence it can behave