The arrangement of electrons in different shells of atoms (electronic configuration) of 18th group elements is shown in the table-1. The valence electrons in the atom of an element is depicted in a short form by Lewis symbol or electron dot structure. We represent the nucleus and inner shell electrons of the atom by the symbol of the element and electrons in the outer shell by dots or cross marks.

Let us see how? Lewis dot structure of argon and sodium atoms are written.

Let us start with argon. Its atom has eight valence electrons.

First write the symbol of element argon. Ar

Place the valence electrons around the symbol. Put two dots at a time on each of the four sides of the symbol of the element till all are used up. So, we get,

Similarly, for sodium, the number of valence electrons in sodium is one and the symbol is Na. We can also use cross mark for the electrons. The Lewis structure for sodium atom is therefore:

The Lewis dot structures of the atoms of noble gases are shown below:

Write the Lewis structures of the given elements in the table. Also consult the periodic table and fill in the group number of the element.