# How can we find in which period and group in the periodic table an element exists. Explain the whole method thoroughly?

By BYJU'S Exam Prep

Updated on: September 13th, 2023

The horizontal rows which were called series by Mendeleev are known as periods and the vertical columns are known as groups.

The elements which have similar outer electronic configurations in their atoms are arranged in vertical columns.

The value of n is indicated by the period for the outermost or the valence shell. The period is equal to the number of shells present in an atom.

To determine a period, number of shells = number of periods

For instance – Na – 2, 8, 1 – 3 shells are present so the period is 3

Ca – 2, 8, 8, 2 – 4 shells are present so the period is 4

To find the group, we have to follow some rules

1. If the element is present in the s block, the group number is equal to the number of valence electrons

For example – Mg (12) = 2, 8, 2

Group number = Number of valence electrons = 2

1. If the element is present in the p block, the number of groups can be found using the formula

Number of valence electrons + 10

For example – S(16) = 2, 8, 6

Group number = Number of valence electrons + 10 = 6 + 10 = 16

1. If the element is present in the d block, the number of groups can be found using the formula

Number of electrons in (n – 1) d subshell + Number of electrons in (n) s subshell

For example – Fe (26) = [Ar] 3d⁶ 4s2

Group number = Number of electrons in (n – 1) d subshell + Number of electrons in (n) s subshell

= 6 + 2 = 8

1. If the element is present in the f block, the number of groups is 3 always.

For example – Cerium (58) belongs to group 3.

Therefore, we can find in which period and group in the periodic table an element exists by following the rules mentioned above.

Summary:

## How can we find in which period and group in the periodic table an element exists? Explain the whole method thoroughly.

We can find in which period and group in the periodic table an element exists by following the rules mentioned above.

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