what are they ?
They are all shiny, soft, highly reactive metals at standard temperature and pressure and readily lose their outermost electron to form cations with charge +1.
Alkali metal
The alkali metals are all shiny, soft, highly reactive metals at standard temperature and pressure and readily lose their outermost electron to form cations with charge +1. 
why alkali metals have low melting and boiling points It is because metal atoms are held together by the electromagnetic attraction from the positive ions to the delocalised electrons.
wiki:1630693
Alkali metal [SEP] Introduction
Experiments have been conducted to attempt the synthesis of ununennium (Uue), which is likely to be the next member of the group; none was successful. However, ununennium may not be an alkali metal due to relativistic effects, which are predicted to have a large influence on the chemical properties of superheavy elements; even if it does turn out to be an alkali metal, it is predicted to have some differences in physical and chemical properties from its lighter homologues.