Lithium and iodine are alike in the sense that they both are only one electron away from having a completed valence electron shell. Lithium only needs to loose 1 electron while iodine only needs to gain 1 electron.
Lithium and iodine are different due to the fact that lithium needs to loose 1 electron therefore having a low electronegativity while iodine only needs to gain 1 electron therefore having a high electronegativity. This difference in electronegativity causes the two elements to react in different ways and have the ability to form different compounds.
I hope this helps. Let me know if anything is unclear.
