What were the criteria used by $Mendeleev$ in creating his Periodic Table?

Helium is an unreactive gas and neon is a gas of extremely low reactivity. What,if anything,do their atoms have in common?

Which element has:
$(a)$ two shells,both of which are completely filled with electrons?
$(b)$ the electronic configuration $2, 8, 2$?

What property do all elements in the same column of the Periodic Table as boron have in common?

The position of three elements $A$,$B$ and $C$ in the Periodic Table are shown below:

Group $16$	Group $17$
-	-
-	$A$
-	-
$B$	$C$

$(a)$ Will $C$ be larger or smaller in size than $B$?
$(b)$ Which type of ion,cation or anion,will be formed by element $A$?

Use Mendeleev's Periodic Table to predict the formulae for the oxides of the following elements: $K, C, Al, Si, Ba$.