First write the electronic configuration z=20=1s2 2s2 2p6 3s2 3p6 4s2 principal quantum number of outer most shell=n=4 so it belongs to 4th period outermost electron enters S Subshell= Sblockelement since the it belongs to S block, group number = number of electrons in S Subshell=2

The element with an atomic number of 20 is calcium (Ca). Calcium is a chemical element that belongs to group 2 and period 4 of the periodic table.

Position in the Periodic Table:
The periodic table is a tabular arrangement of chemical elements based on their atomic numbers. It is divided into rows called periods and columns called groups. Each element is represented by its atomic number, symbol, and atomic weight.

Period:
The period of an element represents the number of electron shells or energy levels it has. Calcium, with an atomic number of 20, is located in period 4 of the periodic table. This means that calcium has four electron shells or energy levels.

Group:
The group, also known as a family, of an element signifies the number of valence electrons it possesses. Valence electrons are the electrons present in the outermost energy level of an atom and determine its chemical properties. Calcium belongs to group 2, which is also known as the alkaline earth metals. Elements in group 2 have two valence electrons.

Block:
The periodic table is further divided into blocks based on the type of orbital in which the valence electrons are located. Calcium is located in the s-block, which consists of elements with valence electrons in the s-orbital.

Visual Representation:
To visually represent the position of calcium (Ca) in the periodic table:

Period: 1 2 3 4 ...
-------------------
Group | H Li Be B C ...
1 | Na Mg ...
2 | K Ca ...

You can notice that calcium (Ca) is in the fourth period, second group, and s-block of the periodic table.

Conclusion:
In conclusion, an element with an atomic number of 20 corresponds to calcium (Ca) in the periodic table. Calcium is located in period 4, group 2, and the s-block of the periodic table.