Question

Explain
Group 17 elements are non-metals, while group 1 elements are metals.

Answer 1

Group 17 elements are non metals because they have 7 electrons in their valence shell and ionize by accepting 1 electron to form an anion.
For example group 17 elements F, Cl, Br and I all have 7 electrons in their valence shell and ionize by accepting 1 electron to form F^-, Cl^-, Br^- and I^-.  
Group 1 elements are metals because they have tendency to lose the one electron present in their valence shell and form positive ion.
For example, group 1 elements Li, Na, K, Rb, Cs have tendency to lose the one electron present in their valence shell and form positive ions Li⁺, Na⁺, K⁺, Rb⁺ and Cs⁺.