Group 17: General properties of halogens (2023)

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    The halogens are to the left of the noble gases on the periodic table. These five toxic non-metallic elements make up group 17 of the periodic table and consist of: fluorine (F), chlorine (Cl), bromine (Br), iodine (I) and astatine (At). Although astatine is radioactive and has only short-lived isotopes, it behaves similarly to iodine and is often classified in the halogen group. Because halogen elements have seven valence electrons, they only need one extra electron to make a full octet. This property makes them more reactive than other non-metal groups.


    Halogens form diatomic molecules (of the form X2, where X denotes a halogen atom) in their elementary states. The bonds in these diatomic molecules are nonpolar single covalent bonds. However, halogens easily combine with most elements and are never seen uncombined in nature. As a general rule, fluorine is the most reactive halogen and astatine is the least reactive. All halogens form Group 1 salts with similar properties. In these compounds, the halogens exist as halide anions with a charge of -1 (for example, Cl-, brother-, etc). Replacing the -ine ending with an -ide ending indicates the presence of halide anions; for example cl-It's called "chloride." In addition, the halogens act as oxidizing agents: they have the property of oxidizing metals. Therefore, most chemical reactions involving halogens are oxidation-reduction reactions in aqueous solution. Halogens in the -1 oxidation state often form single bonds with carbon or nitrogen in organic compounds. When in an organic compound a halogen atom is replaced by a covalently bonded hydrogen atom, the prefix isWarzenhofcan be used in general, or the prefixesFluorine-,chlorine-,Brom-, ojod-can be used for specific halogen replacement. Halogen elements can join to form diatomic molecules with single polar covalent bonds.

    Cloro (Kl2) was the first halogen, discovered in 1774, followed by iodine (I2), Brom (Br2), flour (F2) and astatine (At, last discovered in 1940). The name "halogen" is derived from the Greek roots hal- ("salt") and -gen ("to form"). Together these words mean "salt formers" and refer to the fact that halogens form salts when they react with metals.Natureis the mineral name for rock salt, a naturally occurring mineral composed primarily of sodium chloride (NaCl). Finally, halogens are also relevant in everyday life, be it the fluoride in toothpaste, the chlorine that disinfects drinking water, or the iodine that enables the production of thyroid hormones in the body.


    fluorine -Fluorine has atomic number 9 and is denoted by the symbol F. Elemental fluorine was first discovered in 1886 by isolating it from hydrofluoric acid. Fluorine exists as a diatomic molecule in its free state (F2) and is the most abundant halogen in the Earth's crust. Fluorine is the most electronegative element on the periodic table. It appears as a pale yellow gas at room temperature. Fluorine also has a relatively small atomic radius. Its oxidation state is always -1 except in its elemental diatomic state (where its oxidation state is zero). Fluorine is extremely reactive, reacting directly with all elements except helium (He), neon (Ne), and argon (Ar). in h2In solution, hydrofluoric acid (HF) is a weak acid. Although fluorine is strongly electronegative, its electronegativity does not determine its acidity; HF is a weak acid because the fluoride ion is basic (pH > 7). In addition, fluoride generates very strong oxidizing agents. For example, fluorine can react with the noble gas xenon to form the strong oxidizing agent xenon difluoride (XeF).2). There are many uses for fluoride, which will be discussed in Part VI of this article.

    chlorine- Chlorine has atomic number 17 and chemical symbol Cl. Chlorine was discovered in 1774 by extraction from hydrochloric acid. In its elemental state it forms the diatomic molecule Cl2. Chlorine has different oxidation states, e.g. B. -1, +1, 3, 5, and 7. At room temperature it appears as a light green gas. Since the bond between the two chlorine atoms is weak, Cl2The molecule is very reactive. Chlorine reacts with metals to produce salts called chlorides. Chloride ions are the most abundant ions dissolved in the ocean. Chlorine also has two isotopes:35Of course37Class Sodium chloride is the most common compound of the chlorides.

    brom- Bromine has an atomic number of 35 with a symbol of Br. It was first discovered in 1826. In its elemental form it is the diatomic molecule Br2. At room temperature, bromine is a reddish-brown liquid. Its oxidation states range from -1, +1, 3, 4, and 5. Bromine is more reactive than iodine but not as reactive as chlorine. Furthermore, bromine has two isotopes:79mercado81Br. Bromine consists of bromide salts found in the sea. World bromide production has increased significantly over the years due to its availability and increased availability. Like all other halogens, bromine is an oxidizing agent and highly toxic.

    Iodine- Iodine has atomic number 53 and symbol I. Iodine has oxidation states -1, +1, 5 and 7. Iodine exists as a diatomic molecule, I2, in its elemental state. At room temperature it appears as a purple solid. Iodine has a stable isotope:127I. It was first discovered in 1811 through the use of algae and sulfuric acid. Currently, iodide ions can be isolated from seawater. Although iodine is not very soluble in water, solubility can be increased when certain iodides are mixed into solution. Iodine plays many important roles in life, including the production of thyroid hormones. This is dealt with in Part VI of the text.

    Astato- Astatine is a radioactive element with atomic number 85 and symbol At. Its possible oxidation states include: -1, +1, 3, 5, and 7. It is the only halogen that is not a diatomic molecule and appears as a black metallic solid at room temperature. Astatine is a very rare element, so not much is known about this element. Furthermore, astatine has a very short radioactive life.half life, not more than a few hours. It was discovered by synthesis in 1940. Furthermore, astatine is believed to be similar to iodine. However, these two elements must differ in their metallic character.

    Table 1.1: Electronic configurations of halogens.
    halogen Electronic configuration
    Fluorine 1s22s22p5
    chlorine [For] 3s23p5
    brom [Ar]3d10 4s2 4p5
    Iodine [Kr]4d105 seconds217h5
    Astato [vehicle] 4f145d106s218:005

    periodic trends

    operiodic trendsobserved in the halogen group:

    Melting and boiling points (part of increases)

    The melting and boiling points increase according to the group.Forcas van der Waal. The size of the molecules increases down the group. This increase in size means an increase in the intensity of the van der Waals forces.

    \[F < Cl < Br < I < At\]

    Table 1.2: Melting and boiling points of the halogens
    halogen Melting point (˚C) boiling point (˚C)
    Fluorine -220 -188
    chlorine -101 -35
    brom -7,2 58,8
    Iodine 114 184
    Astato 302 337

    atomic radio (moves down the group)

    The size of the kernel increases by one group (F <Cl <Br <I <At)Because the number of protons and neutrons increases. Also, more energy levels are added with each spell. This results in a larger orbital and therefore a longer atomic radius.

    Table 1.3: Atomic radius of the halogens
    halogen Radio Kovalenter (pm) Ionenradio (X-) (pm)
    Fluorine 71 133
    chlorine 99 181
    brom 114 196
    Iodine 133 220
    Astato 150

    Ionization energy (dreduce group)

    If the outer valence electrons aren't close to the nucleus, it doesn't take as much energy to remove them. Therefore, the energy required to remove the outermost electron is not as high for elements at the bottom of the group because there are more energy levels. Also, the high ionization energy makes the element appear non-metallic. Iodine and astatine exhibit metallic properties, i.e.ionization energydecreases the group (Em < I < Br < Cl < F).

    Table 1.4 Ionization energy of halogen
    halogen First ionization energy (kJ/mol)
    FLuorina 1681
    chlorine 1251
    brom 1140
    Iodine 1008
    Astato 890±40

    electronegativity (ie.reduce group)

    The number of valence electrons in an atom increases in the group as the energy levels increase to lower and lower levels. The electrons are progressively moving away from the nucleus; Therefore, the nucleus and the electrons are not so attracted to each other. An increase in shielding is observed. Therefore, the electronegativity decreases in the group (Em < I < Br < Cl < F).

    Table 1.5: Electronegativity of the halogens
    halogen electronegativity
    Fluorine 4.0
    chlorine 3.0
    brom 2.8
    Iodine 2.5
    Astato 2.2

    Electron affinity (i.e.,reduce group)

    As the atomic size increases down the group,Electronic affinityusually decreases (em < yo < br <F<CL). An electron is not as strongly attracted to the nucleus, resulting in a low electron affinity. However, fluorine has a lower electron affinity than chlorine. This can be explained by the small size of fluorine compared to chlorine.

    Table 1.6: Electron affinity of the halogens
    halogen Electron affinity (kJ/mol)
    Fluorine -328,0
    chlorine -349,0
    brom -324,6
    Iodine -295,2
    Astato -270,1

    Reactivity of the elements (i.e.reduce group)

    Halogen reactivities decrease throughout the group.(em < yo < br <Kl<F). That is becauseAtomic radius increases with increasing electronic energy. This reduces the attraction for valence electrons from other atoms and reduces reactivity. This decrease also occurs becauseelectronegativitydecreases a group; therefore, there is less "pull" for electrons. In addition, the oxidation capacity decreases throughout the group.

    Hydrogen halides and halooxoacids

    hydrogen halides

    A halide is formed when a halogen reacts with another less electronegative element to form a binary compound. For example, hydrogen reacts with halogens to form halides in the formHX:

    • Hydrogen fluoride: HF
    • Clorwasserstoff: HCl
    • Bromwasserstoff: HBr
    • Hydrogen iodide: HI

    Hydrogen halides readily dissolve in water to form hydrogen halides (hydrofluoric acid,hydrochloric acid,Bromide,jodwasserstoff) acids. The properties of these acids are given below:

    • Acids are formed by the following reaction: HX(aq) + H2Mich)X-(and) + H3o+(ac)
    • All hydrogen halides except HF form strong acids.
    • The acidity of hydrohalic acids increases as follows: HF < HCl < HBr < HI

    Hydrofluoric acid can attack glass and certain inorganic fluorides over a long period of time.

    It may seem counterintuitive to say that HF ​​is the weakest hydrohalic acid because fluorine has the highest electronegativity. However, the H-F bond is very strong; YeahThe H-X bond is strong, the resulting acid is weak. A strong bond is characterized by a short bond length and a large bond dissociation energy. Of all the hydrogen halides, HF has the shortest bond length and the highest bond dissociation energy.


    Aoxo acid halogenIt is an acid with hydrogen, oxygen and halogen atoms. The acidity of an oxoacid can be determined by analyzing the structure of the compound. The halooxoacids are given below:

    • Hypochlorous acid: HOCl
    • Chlorous acid: HClO2
    • Chloruro: HClO3
    • Perchloric Acid: HClO4
    • Hypobromous acid: HOBr
    • Bromsäure: HBrO3
    • Perbromsäure: HBrO4
    • Hypoiodic acid: HOI
    • Jodsaure: HIO3
    • Metaperíodo: HIO4; H5ES6

    In each of these acids, the proton is attached to an oxygen atom; therefore, a comparison of proton bond lengths is meaningless in this case. Instead, electronegativity is the dominant factor in the oxoacid. The strength of the acid increases with more oxygen atoms attached to the central atom.

    States of matter at room temperature

    Table 1.7: Physical states and appearance of halogens
    States of matter (at room temperature) halogen Look
    Solid Iodine Permission
    Astato schwarz/metallic[Supposed]
    Liquid brom Reddish brown
    Gas Fluorine hell gelbbraun
    chlorine pale green

    appearance explanation

    The colors of the halogens are the result of the absorption of visible light by the molecules, causing an electronic excitation. Fluorine absorbs violet light and therefore appears pale yellow in color. Iodine, on the other hand, absorbs yellow light and appears violet (yellow and violet are complementary colors that can be determined with aFarbkreis).The colors of the halogens darken in the group:

    In closed containers, liquid bromine and solid iodine are in equilibrium with their vapours, which often appear as colored gases.Although the color of astatine is unknown, based on past trends, it is believed that astatine should be darker than iodine violet (ie black).

    Oxidation states of halogens in compounds.

    Halogens usually have aOxidation stateof 1. However, when halogen is attached to oxygen or another halogen, it can assume different states: the -2 rule for oxygen takes precedence over this rule; in the case of two different halogens bonded together, the more electronegative atom takes precedence and assumes the -1 oxidation state.

    Example 1.1: Iodine chloride (ICl)

    Chlorine has an oxidation state of -1 and iodine has an oxidation state of +1. Chlorine is more electronegative than iodine, giving it the -1 oxidation state.


    Oxygen has a total oxidation state of -8 (-2 charge x 4 atoms = -8 total charge). Hydrogen has a total oxidation state of +1. Adding these two values, the total oxidation state of the compound to date is -7. Since the final oxidation state of the compound must be 0, the oxidation state of bromine is +7.

    A third exception to the rule is this: when a halogen in its elemental form (X2), its oxidation state is zero.

    Table 1.8: Oxidation states of the halogens
    halogen Oxidation States in Compounds
    Fluorine (always) -1*
    chlorine -1, +1, +3, +5, +7
    brom -1, +1, +3, +4, +5
    Iodine -1, +1, +5, +7
    Astato -1, +1, +3, +5, +7

    Example 1.3: fluoride

    Why does fluorine always have the -1 oxidation state in its compounds?


    Electronegativity increases with time and decreases in a group. Therefore, fluorine has the highest electronegativity of all the elements, as indicated by its position on the periodic table. Its electronic configuration is 1s.22s22p5. When fluorine gains one more electron, the outermost p orbitals become completely filled (resulting in a full octet). Because fluorine has high electronegativity, it can easily remove the desired electron from a nearby atom. Therefore, fluorine is isoelectronic with a noble gas (having eight valence electrons); all of its outermost orbitals are filled. Fluorine is much more stable in this state.

    halogen applications

    Fluorine: Although fluorine is highly reactive, it serves many industrial purposes. For example, it is an important component of plastic.polytetrafluoroethylene(calledTeflon-TFEby DuPont) and certain other polymers often referred to as fluoropolymers. Chlorofluorocarbons (CFCs) are organic chemicals that were used as refrigerants and propellants in aerosols before growing concerns about their potential environmental impact led to their phaseout. Instead, hydrochlorofluorocarbons (HFCs) are now used. Fluoride is also added to toothpaste and drinking water to reduce cavities. Fluoride is also found in the clay used in some ceramics. Fluorine is also associated with nuclear power generation. Also, it is used to make fluoroquinolones, which are antibiotics. Below is a list of some important inorganic fluorine compounds.

    Table 1.9: Important inorganic fluorine compounds
    compound usos
    Of3AlF6 aluminum fabrication
    Freund3 Catalyst
    c y f2 Optical components, RF manufacturing, metallurgical flow
    CLF3 Fluorinating agents, nuclear fuel reprocessing
    OF F manufacturing2, AlF3, of3AlF6, y Fluorcarbonetos
    LiF Ceramic fabrication, brazing and soldering
    NaF Fluoridated water, dental prophylaxis, insecticide
    SF6 Insulating gas for high voltage electrical equipment
    SNF2 toothpaste manufacturing
    UF6 Production of uranium fuel for nuclear reactors

    chlorine: Chlorine has many industrial uses. It is used to disinfect drinking water and swimming pools. Sodium hypochlorite (NaClO) is the main ingredient in bleach. Hydrochloric acid, sometimes called hydrochloric acid, is a commonly used acid in industry and laboratories. Chlorine is also present in polyvinyl chloride (PVC) and several other polymers. PVC is used to insulate cables, pipes, and electronic devices. Chlorine is also very useful in the pharmaceutical industry. Chlorine-containing medications are used to treat infections, allergies, and diabetes. The neutralized form of the hydrochloride is a component of many medications. Chlorine is also used to sterilize hospital machinery and limit the growth of infections. In agriculture, chlorine is a component of many commercial pesticides: DDT (dichlorodiphenyltrichloroethane) was used as an agricultural insecticide, but its use has been phased out.

    brom: Bromine is used in flame retardants for its refractory properties. It has also been found in the pesticide methyl bromide, which makes it easier to store cultures and prevents bacteria from multiplying. However, the excessive use of methyl bromide has stopped due to its effects on the ozone layer. Bromine is also involved in the production of gasoline. Other uses for bromine include making photographic film, the content of fire extinguishers, and medicines used to treat pneumonia and Alzheimer's disease.

    Iodine: Iodine is important for the proper functioning of the body's thyroid gland. If the body does not get enough iodine, a goiter (enlarged thyroid gland) forms. Table salt now contains iodine to promote the proper functioning of thyroid hormones. Iodine is also used as an antiseptic. Solutions used to clean open wounds likely contain iodine, and it is often found in disinfectant sprays. Silver iodide is also important for photographic development.

    Astato: Because astatine is radioactive and rare, there are no documented uses for this halogen element. However, it is speculated that this element may help iodine regulate thyroid hormones. Also,211It has been used in mice to help in the study of cancer.

    VIII. external links

    • Grube, Karl; Leffler, Amos J. "Synthesis of Metal Halides (ML)".J.Chem. educator 1993,70, A204.
    • This video provides information on some of the physical properties of chlorine, bromine, and iodine:
    • The following video compares four halogens: fluorine, chlorine, bromine, and iodine in terms of chemical reactions and physical properties.
    • Circle of color mentioned in the text:
    • Elson, Jess. "A binding parameter. III, Water solubilities and melting points of alkali halogens". J.Chem. Ed. 1969, 46, 86.
    • Fessende, Elizabeth. "Structural Chemistry of Interhalogen Compounds". J.Chem. Education 1951, 28, 619.
    • Holbrook, Jack B.; Sabry-Grant, Ralph; Smith, Barry C.; Tandel, Thakor V. "Lattice Enthalpies of Ionic Halides, Hydrides, Oxides, and Sulfides: Second Electron Affinities of Atomic Oxygen and Sulfur." J.Chem. Education 1990, 67, 304.
    • Kildahl, Nicholas K. "A method for determining formulas for the simple p-block oxoacids." J.Chem. Education 1991, 68, 1001.
    • Liprandi, Domingo A.; Reinheimer, Orlando R.; Paredes, Jose F.; L'Argentière, Pablo C. "A simple and safe way to prepare halogens and study their visual properties in a technical high school." J.Chem. Education 1999 76
    • Meek, Terry L. "Acidity of Oxoacids: Correlation with Charge Distribution." J.Chem. Education 1992, 69, 270.

    practical problems

    1. Why does fluorine always have the -1 oxidation state in its compounds?
    2. Find the oxidation state of the halogen in each problem:
      1. HOCl
      2. kio3
      3. F2
    3. What are the three uses of chlorine?
    4. What element(s) exists as a solid at room temperature?
    5. Does the following increase or decrease the halogen group?
      1. boiling point and melting point
      2. electronegativity
      3. ionization energy


    1. Electronegativity increases with time and decreases in a group. Therefore, fluorine has the highest electronegativity of all the elements. Because fluorine has seven valence electrons, only one more electron is needed to achieve a noble gas configuration (eight valence electrons). Therefore, it will be more likely to extract an electron from a nearby atom.
    2. Disinfection of water, pesticides and medicines
      1. +1 (Hydrogen has a +1 oxidation state and oxygen has a -2 oxidation state. So chlorine must have a +1 oxidation state for the total charge to be zero.)
      2. +5 (The oxidation state of potassium is +1. Oxygen has an oxidation state of -2, so for this compound it is -6 (-2 charge x 3 atoms = -6). Since the general oxidation must be zero, the oxidation state of iodine must be +5).
      3. 0 (elementary forms always have an oxidation state of 0).
    3. iodine and astatine
      1. increase
      2. decreases
      3. decreases


    1. Hill, Graham, and John Holman. chemistry in context. 5th ed. UK: Nelson Thornes, 2000. 224-25.
    2. Petrucci, Ralph H. General Chemistry: Principles and Modern Applications. 9th Edition New Jersey: Pearson Education Inc., 2007. 920-928.
    3. Verma, N.K., B. Kapila, and S.K. Chana. Integral Chemistry XII. Nova Deli: Laxmi Publications, 2007. 718-30.
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