Why does iodine exhibit metallic properties at room temperature although being a non-metal? Are there any similar elements like this?
Iodine is a metalloid. Metalloid elements have one or more allotropes with properties intermediate between those of a metal and a nonmetal.
Metals are lustrous, ductile, and conductive of heat and electricity.
Nonmetals are matte, brittle, and insulators.
Metalloids may be semiconductors, like silicon, germanium, arsenic, and carbon (graphite). They may be lustrous, but brittle, like iodine and tellurium.
All such trends are attributed to periodicity in properties Generally, going down a group in periodic table metallic character increases which is attributed to the dominance of addition of new principal quantum number over increasing nuclear charge.This results in increasing size of atoms which in turn results in lowering of ionization enthalpy (a parameter that may be used to judge upon metallic nature:lower the ionisation enthalpy,higher the metallic nature).Since ionistation enthapy is inversely proportional to size,hence it decreases down a Group.
That's why in Halogen family Iodine possess metallic character to some extent. However these terms become relative if we universalize them.For example there are compounds of Iodine like
Fluorides Iodine fluoride: IF Iodine trifluoride: IF3 Iodine pentafluoride: IF5 Iodine heptafluoride: IF7
Chlorides Iodine chloride: ICl Diiodine hexachloride: [ICl3]2
where Iodine shows metallic character.At the same time we too have
NaI,KI etc. where it acts as a non metal.Hence it become more logical to say it to be a metalloid.(Since also across a Period metallic character decreases.So the two effects viz General increase in metallic character down a group and decrease in it across a period compensate.