Why do atoms of Group 1 elements lose electrons to form cations where as atoms of Group 17 elements gain electrons to form anions

In order for a high temperature boiler or steam engine to produce superheated water, or steam: the heat source must be greater than 100°c the water must be permitted to evaporate quickly the system must be sealed and become pressurized above atmospheric pressure the vapor pressure must be kept below 760 mm(hg)