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These elements are diatomic molecules in their natural form. They require one more electron to fill their outer electron shells, and so have a tendency to form a singly-charged negative ion. This negative ion is referred to as a halide ion; saltsFor other meanings of the word salt see salt (disambiguation In chemistry, a salt is a composed of positively charged cations and negatively charged anions, so that the product is neutral and without a net charge. They are typically the product of a chemi containing these ions are known as halidesA halide is a binary compound, of which one part is a halogen atom and the other part is an element or radical that is less electronegative than the halogen. Most salts are halides. All Group I Earth metals form halides with the halogens and they are whit.
Halide ions combined with single hydrogen atoms form the hydrohalic acidFor alternative meanings see acid (disambiguation). An acid (represented by the generic formula AH is typically a water-soluble, sour-tasting chemical compound. An acid always has a pH of less than 7. It is a molecule or ion that contains hydrogen or thats (i.e., HF, HCl, HBr, HI), a series of particularly strong acids. (HAt, or "astatinic acid", could be called hydrohalic, but since all known isotopeIsotopes are atoms of a chemical element whose nuclei have the same atomic number, Z but different atomic weights, A''. The word isotope meaning at the same place comes from the fact that isotopes are located at the same place on the periodic table. The as of astatine are radioactiveRadioactive decay Radioactivity is the process by which unstable atomic nuclei decay. This process normally produces ionizing radiation with a relatively large amount of energy. This energy can be harnessed in the form of nuclear power, or it can be very and have half-livesThis article describes the scientific meaning. For the computer game, see Half-Life''. For a quantity subject to exponential decay, the half-life is the time required for the quantity to fall to half of its initial value. Quantities subject to exponential ranging from eight hours to less than a minute, it is not typically included in discussions of hydrohalic acids.)
They react with each other to form interhalogenThe halogens react with each other to form interhalogen compounds. The interhalogens of form XY have physical properties intermediate between those of the two parent halogens. The covalent bond between the two atoms has some ionic character, the less elec compounds.
Many synthetic organic compoundAn organic compound is any of a large class of chemical compounds whose molecules contain carbon, with exception of carbides, carbonates and carbon oxides. Organic compounds are studied in organic chemistry; many of them, such as proteins, fats, and carbos, and a few natural ones, contain halogen atoms; these are known as halogenated compounds. Thyroid hormones contain iodide atoms. Chloride ions play a key role in brain function by mediating the action of the inhibitory transmitter GABA.
They show a number of trends when moving down the group - for instance, decreasing electronegativity and reactivity, increasing melting and boiling point.
| Halogen | Melting Point | Boiling Point | Electronegativity |
|---|---|---|---|
| Fluorine | 53.53 | 85.03 | 3.98 |
| Chlorine | 171.6 | 239.11 | 3.16 |
| Bromine | 265.8 | 332.0 | 2.96 |
| Iodine | 396.85 | 457.4 | 2.66 |
| Astatine | 575 | ? | 2.2 |
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