The halogens have seven electrons in their outermost shell. Each halogen atom lacks a single electron to make their octet a complete one. Elements in the halogen group are univalent and also acceptors of electrons. They are all non-metals and oxidizing agents. The oxidizing power of the halogens decreases from top to down the group. This is why the more powerful halogens displaces a less powerful one from simple salts.
Electromagnetic waves are not like sound waves because they do not need molecules to travel. This means that electromagnetic waves can travel through air, solid objects and even space.