Content Strategy Manager
Halogens are the group 17 elements of the periodic table. The term ‘halogen’ means ‘salt-producing’, hence the name halogens as they possess the tendency to form salts after reacting to metals. It generally has five elements - Fluorine (F), Chlorine (Cl), Bromine (Br), Iodine (I), and Astatine (At). These are all naturally occurring halogens but Tennessine (Ts) is an artificially created halogen. In this article, we will study more about the general properties, general characteristics, position in the periodic table, oxidation state etc of the halogens.
Key Terms: Halogens, Reactivity, Oxidation State, Electronegativity, Ionic Bond, Covalent Bond, Group 17 Elements, Bromine
What are Halogens?
[Click Here for Sample Questions]
Halogens are highly reactive elements and are highly electronegative. They have a high tendency to react with metals to form salts. They are also known as Group 17 elements. They have 7 electrons in their outer shell with a configuration of (ns2 np5). Fluorine being the first halogen in group 17, is highly reactive. Astatine is a halogen because of its resemblance with iodine despite it being radioactive.
Position of Halogens in Periodic Table
Electronic Configuration of Halogens
[Click Here for Sample Questions]
The general electronic configuration for group 17 elements is ns2np5. This configuration clearly shows that they have 7 electrons in their valence shell. They require one more electron to complete their octet and achieve noble gas configuration. This accounts for their higher reactivity and tendency to gain one electron and form ionic bonds or share electrons with other elements to form covalent bonds.
Electronic Configuration of Halogens
Elements of Group 17
[Click Here for Sample Questions]
The elements of group 17 along with their general properties are mentioned below:
Fluorine: It is represented by F and it has the atomic number 9. It is the first halogen in the periodic table and was discovered in 1530 by Georgius Agricola. Fluorine is mainly found in the earth’s crust and the main source is Fluorspar for industry purposes.
Fluorine
Chlorine: Chlorine is the 2nd halogen in the periodic table which is represented by Cl and has atomic number 17. It does not exist as a pure element, rather it is found as compounds with other elements due to its high reactivity. It is mainly found in rock salt (NaCl), sylvite (KCl), etc and is also found in the lithosphere.
Chlorine
Bromine: It is represented by the symbol Br and has the atomic number 35. It is always found as a halide compound due to its high reactivity. The ocean is the main source of bromine and is mainly produced by the USA, Germany and Israel.
Bromine
Iodine: Iodine is represented by the symbol I and has the atomic number 53. It is found as iodates and iodide compounds. It is mainly found in rocks, soil, sea, etc.
Iodine
Astatine: It is the only radioactive element which is represented by At and has atomic number 85. It is a very rare element and is not generally found in nature. It can be prepared artificially by bombarding bismuth-209 with alpha particles.
Astatine
General Characteristics of Halogens
[Click Here for Sample Questions]
Mentioned below are some of the general characteristics of halogens:
- Halogens are very reactive in nature.
- Due to such high reactivity halogens are not found in nature as pure elements, rather they are found as a compound with other elements or as ions.
- Most halogens are found together with other elements as salts in sea and water bodies because of their reactivity.
- Halogens are the only elements which can be found in all three forms in nature. At normal temperature and pressure - chlorine and fluorine are gases, bromine is a liquid and iodine and astatine are solids.
- Halogens have a tendency to form hydrogen halides, which are potent acids when they combine with hydrogen.
- The halogens can react among themselves to form diatomic interhalogen compounds.
Atomic Properties of Halogens
[Click Here for Sample Questions]
Mentioned below are the atomic properties of halogens:
- Ionic and Atomic Radii: Nuclear Radii, as well as atomic radii, keep on increasing as we move vertically down in the group. They have the smallest size among all the elements in the row. The size of halogens varies as F < Cl < Br < I < At.
| Halogens | Covalent Radius (pm) | Ionic Radius (pm) |
|---|---|---|
| Fluorine | 71 | 133 |
| Chlorine | 99 | 181 |
| Bromine | 114 | 196 |
| Iodine | 133 | 220 |
| Astatine | 155 | - |
- Ionisation Enthalpy: The ionisation energy of halogens is quite high compared to other elements in the row. Ionisation enthalpy decreases as we move down the group because more energy levels are added which are away from the nucleus. Even if the value decreases down the group, the values are high. Fluorine has comparably very high ionisation enthalpy due to its small size.
| Halogens | Ionisation Enthalpy (kJ/mol) |
|---|---|
| Fluorine | 1681 |
| Chlorine | 1251 |
| Bromine | 1140 |
| Iodine | 1008 |
| Astatine | 890 |
- Electron Gain Enthalpy: The electron gain enthalpy is negative for halogens because they have a high affinity for electrons. E.G enthalpy becomes less negative moving down the group. However, Fluorine is an exception having electron gain enthalpy lesser than chlorine because of fluorine’s small size and more repulsion.
- Electronegativity: Halogens have high electronegativity values because they are one electron less than the stable octet configuration. They keep decreasing down the group. Because the newer energy levels are added and the nucleus has less influence on outer shells, the nucleus and the electrons are less attracted to each other. The electronegativity order is At < I < Br < Cl < F.
Physical Properties
Mentioned below are the physical properties of halogens:
- Physical State: Halogens exist in all three forms - solid, liquid, and gas. Fluorine and Chlorine are gas at room temperature, bromine is liquid, and Astatine and Iodine are solid. When liquid bromine and solid iodine are kept in closed-lid containers, there is an equilibrium between them and their vapours.
- Colour: The colour of halogens comes due to the absorption of visible light by the molecules. Fluorine is pale yellow in colour, Chlorine is pale green, bromine is a reddish-brown liquid, Iodine is violet and astatine is black metallic in colour.
- Solubility: Chlorine and Fluorine are soluble in water but iodine and bromine are not soluble.
- Melting Points: Melting and boiling points of halogens increase down the group. Thus fluorine has the lowest boiling and melting point, Iodine has the highest.
Chemical Properties
Mentioned below are the physical properties of halogens:
- Oxidising Power: All the halogens are good oxidising agents due to their high electron affinity. Fluorine is the most powerful oxidising agent in the periodic table. It can oxidise almost every other halide ion of the solution. The oxidation power decreases down the group.
- Reaction with Hydrogen: Halogens form acidic halides after reacting with hydrogen. The acidity of halides increases down the group. HI is the most acidic halide. Fluorine reacts violently with hydrogen, chlorine requires UV light to react, bromine reacts on heating, and iodine requires a catalyst to react.
- Reaction with Oxygen: Halogens form oxides after reacting to oxygen. Fluorine readily reacts with oxygen to form difluorine oxide(F2O) but other halogens are less reactive with oxygen. Halogens also form oxoacids after reacting to compounds containing Hydrogen and oxygen. Some examples of oxoacids are - hypochlorous acid (HOCl), chlorous acid (HClO2), and Chloric acid (HClO3).
- Reaction with Metals: Halogens are very much reactive towards metals. They react with most metals to form resulting metal halides. Metal halides are ionic in nature. For example, chlorine reacts with sodium metal and forms sodium chloride. This reaction that happened here is exothermic.
Oxidation States
Halogens show a wide range of oxidation states as tabulated below:
| Halides | Oxidation States |
|---|---|
| Fluorine | -1 |
| Chlorine | -1,+1,+3,+5,+7 |
| Bromine | -1,+1,+3,+4,+5 |
| Iodine | -1,+1,+5,+7 |
| Astatine | -1,+1,+3,+5,+7 |
Uses of Halogens
[Click Here for Sample Questions]
Mentioned below are the uses of halogens in our day-to-day life:
- Despite being highly reactive, fluorine has many industrial applications. It is used to make polymers such as polytetrafluoroethylene, CFCs, fluoropolymers, etc.
- Chlorine is used to disinfect drinking water, to sterilise hospital equipment. DDT, an extensively used pesticide, is manufactured with chlorine.
- Bromine is found in some pesticides like methyl bromide and is used in flame retardants due to its flame-resistant properties.
- Iodine is important for the thyroid gland in our body. Iodine is also used as an antiseptic.
Read More:
Things to Remember
- The term “halogen” means “salt-producing” because of their tendency to form salts after reacting to metals
- Halogens have 7 electrons in their outer shell with a configuration of (ns2 np5).
- Ionisation enthalpy decreases as we move down the group because more energy levels are added which are away from the nucleus.
- Fluorine is an exception having electron gain enthalpy lesser than chlorine because of fluorine’s small size and more repulsion.
- The electronegativity order is At < I < Br < Cl < F.
- Fluorine is pale yellow in colour, Chlorine is pale green, bromine is a reddish-brown liquid, Iodine is violet and astatine is black metallic in colour.
- Fluorine reacts violently with hydrogen, chlorine requires UV light to react, bromine reacts on heating, and iodine requires a catalyst to react.
- Halogens form oxides after reacting to oxygen.
Sample Questions
Ques. Cl2 has more negative electron gain enthalpy than F2. Why? (3 Marks)
Ans. Halogens are considered to be good oxidising agents because of their high electronegativity values. With the increase in atomic size the electron gain enthalpy increases. It is expected that fluorine should have low electron gain enthalpy due to its small size but the electron gain enthalpy of chlorine is more negative than fluorine. This is because of the fact that the size of fluorine is so small that the incoming electron gets repulsive forces from the nucleus. This is why Cl2 has more negative electron gain enthalpy than F2.
Ques. What are polyhalogenated compounds? (3 Marks)
Ans. Compounds which contain multiple halogen atoms are called polyhalogenated compounds. These compounds are mostly used in industries and are only created for industrial purposes. These compounds are generally toxic and bioaccumulated in humans. DDT is the most common polyhalogenated compound. It is dichloro diphenyl trichloroethane and is a very famous insecticide. Some other examples are - Freons(CFC), CCl4, Iodoform, etc.
Ques. How is astatine different from other halogens? (3 Marks)
Ans. Astatine is the heaviest element in group 17. It is the only radioactive element among the halogens. It is not naturally found in nature and is created by bombarding Bismuth-209 with alpha particles. It has a half-life of 8.3 hours. Unlike other halogens, astatine is not diatomic.
Astatine has no uses in industry as it is radioactive and toxic, though other halogens have a vast applications in industries.
Ques. Halogens are good oxidising agents. Explain. (3 Marks)
Ans. Halogens are found to be very good oxidising agents. This means they raise the oxidation state of other elements. In oxidising other elements, the halogens themselves get reduced. Because they undergo reduction, they become electronically stable and are therefore good oxidising agents. For example, halogens can react with other elements and can form halides such as fluorides, chlorides, iodides, etc
Ques. What is iodoform? Write its uses. (3 Marks)
Ans. The IUPAC name for iodoform is triiodomethane. It is pale yellow in colour and has a saffron-like smell. This is a polyhalogenated compound and was earlier used as an antiseptic. Later it was found that the antiseptic properties are due to the free iodine and not the iodoform itself, so now different compounds containing iodine are used as antiseptic.
Ques. Write some important industrial uses of fluorine. (5 Marks)
Ans. Chlorine has a special property to act as a disinfectant which is widely used in water tanks and other water containers. Chlorine is used to make chlorine bleach used in households which whitens and disinfects clothes and other objects. Chlorine is used in making DDT, which is a very popular pesticide. Chlorinated solvents are often used as an extraction medium in pharmaceutical processes, mining, plastic processing, manufacture of adhesives, varnish remover, etc.
Due to its high reactivity, it is often used to separate metals such as copper, lead, zinc, nickel, etc from their respective ores. Medical equipment mostly contains chlorine such as blood bags, sterile tubes and heart catheters.
Ques. Determine the reaction of halogens with hydrogen. (3 Marks)
Ans. Halogens react with hydrogen and produce gases as a result. Below mentioned is the reaction:
- Hydrogen + Halogen = Hydrogen Halide
- Hydrogen + Chlorine = Hydrogen Chloride
- Hydrogen + Bromine = Hydrogen Bromide
- Hydrogen + Iodine = Hydrogen Iodide
Check-Out:
Comments