The chemical reactivity of the halogens is due to the number of electrons in the outermost energy levels of their atoms. Fluorine is the most active halogen. They have low melting points and boiling points. In the gas phase they exist as diatomic elements. Halongens combine readily with metals to form a class of compounds known as salts.
Noble Gasses are colorless gasses that are extremely unreactive.
Because do not readily combine with other elements to form compounds, the noble gasses are called inert. The family of noble gasses includes helium, neon, argon, krypton, xenon, and radon. All the noble gasses are found in small amounts in the earth's atomsphere. One important property of the noble gasses is their inactivity. They are inactive because their outermost energy level is full.