Group 17 elements: These elements are located on the rightmost side of the periodic table and are known as halogens. They are highly reactive and form diatomic molecules. Halogens have a high electronegativity, which means they have a strong tendency to attract electrons. This makes them extremely reactive, as they readily form bonds with other elements.

Group 1 metals: These elements are located on the leftmost side of the periodic table and are known as alkali metals. They are highly reactive and form monoatomic ions. Alkali metals have a low electronegativity, which means they have a strong tendency to lose electrons. This makes them very reactive, as they readily give up their outermost electron to other elements.

Comparison:

- Electronegativity: Group 17 elements have a high electronegativity while Group 1 metals have a low electronegativity.

- Reactivity: Group 17 elements are highly reactive and form diatomic molecules while Group 1 elements are highly reactive and form monoatomic ions.

- Ionization energy: Group 17 elements have a high ionization energy while Group 1 elements have a low ionization energy.

- Melting and boiling points: Group 17 elements have low melting and boiling points while Group 1 metals have high melting and boiling points.

In summary, the main reason why Group 17 elements are strong non-metals while Group 1 metals are highly reactive metals is due to their differences in electronegativity.