On moving across a period, nuclear pull increases because valence shell electrons increase across a period, and the tendency to lose these electrons will get decreases which means elements cannot lose their electrons easily. Hence, Group $$ 17 $$ elements are strong non-metals, while Group $$ 1 $$ elements are strong metals. For groups $$1$$ element there is less nuclear attraction and group elements can easily lose these electrons hence group $$1$$ are strong metals.