atomic structure - why only hydrogen be separately written in periodic table [duplicate]

The other exception is hydrogen. It has only one s-electron and hence can be placed in group 1 (alkali metals). It can also gain an electron to achieve a noble gas arrangement and hence it can behave similar to a group 17 (halogen family) elements. Because it is a special case, we shall place hydrogen separately at the top of the Periodic Table

lithium can also loose one electron and behave like a noble element so should we also place all ns1 and ns2 element separately at top ?

$\begingroup$ You neglected question preparation. How many electrons does H atom need to gain electron configuration of the next noble gas? And Li atom? $\endgroup$

$\begingroup$ While most alkali metals do form anions, these do not have a noble gas configuration. Only hydride ion from this group does. Also hydride ions exist in a radically different environment from natride and heavier congeners. $\endgroup$

$\begingroup$ In short, H and He are the two having 1s electrons configuration. It is quite natural to place them in the same period. $\endgroup$