Periodic Classification of Elements Test - 9

All the elements of group 18 have 8 valence electrons each in their atoms, except helium which has only 2 valence electrons in its atom as its duplet is complete. 

Mendeleev left proper gaps in his periodic table for the then undiscovered elements, and when Gallium(Ga)  was discovered it was placed in one of those gaps without disturbing the existing elements. 

An element with atomic no 3 has electronic configuration 2,1 i.e. it can lose one electron readily to complete its duplet. 

The element with atomic no 17 has electronic configuration 2,8,7 and is ready to accept one electron to complete its octet. 

So,  both of them with valency 1 combine and the formula is LiCl. 

They are called Periods and we have seven periods in the long form of periodic table. 

Neon(Ne)  with atomic number 10 has an inert gas configuration 2,8 where both the shells have completely filled electrons. 

The elements on the left hand side are most metallic and as we go down the group the metallic character of elements increases.
So, element C has the highest metallic character. 

The elements on the left side have the largest atomic size and as we go down the group the atomic size increases.
Therefore, C has the maximum atomic size. 

The elements on the right side of the table are highly electronegative and as we go down the group electronegativity decreases. Therefore, element B is highly electronegative. 

The elements of group 1 are called alkali metals as they have one electron in their outermost shell and readily lose that electron to form positive ions.