halogen

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From http://www.chemicalelements.com/groups/halogens.html:

The halogens are five non-metallic elements found in group 17 of the periodic table. The term "halogen" means "salt-former" and compounds containing halogens are called "salts". All halogens have 7 electrons in their outer shells, giving them an oxidation number of -1. The halogens exist, at room temperature, in all three states of matter:

• Solid- Iodine, Astatine
• Liquid- Bromine
• Gas- Fluorine, Chlorine

The Halogens are:

• Fluorine
• Chlorine
• Bromine
• Iodine
• Astatine

Of most interest to our industry are the gaseous forms of Bromine and Iodine, used in Stage/Studio lamps due to the Halogen Cycle.