Question

An element with atomic number 21. what is the place of the element in the periodic table? why​

Answer 1

Answer :

• The element with atomic number 21 will lie in 4th period and 3rd group.

Step-by-step explanation:

Given : Element has 21 atomic number

To find : Position of element in periodic table

Explanation :

Let's start the question by understanding basics of periodic table.

• It is a table created by Henry Moseley in which all the elements are placed. It has 7 horizontal columns which are called periods and 18 vertical columns called groups.

• The given atomic number of element is 21.

It's electronic configuration will be 2, 8, 8, 3.

• Now the property of periodic table is that number of shells increased when moving down the period or as increasing the number of periods. The first period has 1 shell in all the elements lying in that period has increases in the succeeding periods.

Since the given element has 4 shells in it's configuration, it will lie in 4th period.

• In periodic table, valence electrons of element increases as by changing of groups. The first period has 1 electrons and increasing 1 by 1 in succeeding groups.

Now the valency of the element is 3 so the element will lie in 3rd group.

Answer 2

The position of the element in the periodic table can be determined as follows.

• Firstly, we know that the Modern Periodic Law given by Moseley states that the physical and chemical properties of elements in the periodic table are periodic function of atomic number. This means that elements with similar properties are arranged in a trend of their atomic number.
• Now, the given element 'X' with atomic number 21 will have a configuration of 2,8,8,3. This shows that the electrons in the atom occupy four atomic shells. As we go down a group, number of shells increase with each period. The element hence lies in the 4th period.
• The valence shell of the atom, that is the N-shell has 3 electrons. Number of valence electrons increase across a period. The element hence belongs to the 3rd group.
• Hence, the given element 'X' belongs to group 3, period 4 of the periodic table.