| Physical Properties:
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- fluorine, a pale yellow gas
- chlorine, a greenish gas, has an irritating odor
- bromine, a red-brown liquid at room temperature
- iodine, a dark grey crystalline solid at room temperature
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| Chemical Properties:
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- the halogens exist as diatomic gas molecules (section 4.7)
- all halogens have seven valence electrons (section 3.3) which form ions with a negative (-1) charge
- fluorine is the most reactive of all the nonmetals
- iodine sublimes when heated
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| Abundance:
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- bromine is obtained by processing brine from wells and from seawater
- iodine is obtained from brine wells and sea plants such as kelp
- astatine is radioactive. Less than 30 grams exist in the Earth's crust. For greater quantities, this element needs to be synthesized in a laboratory.
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| Common
Compounds and Usages:
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- fluorine is a key ingredient in teflon, a fluorocarbon polymer
- chlorine, in low level, is used to purify drinking water. In high concentrations, it is poisonous
- chlorine is used in production of paper, textiles, bleaches, medicines, insecticides, paints, plastics
- bromine is used in photographic chemicals, dyes, fire retardants and in pharmaceutical products
- iodine compounds are used in producing iodized salt, photographic chemicals and in medicines
- iodine is required in human body in order to make the hormone thyroxin
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