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Group 17 Elements: The Halogens

Last Updated : 25 Feb, 2022
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The Halogens are the elements in the periodic table of Group 17 of the periodic table. Fluorine, chlorine, bromine, and iodine are examples of reactive nonmetals. Halogens are nonmetals that are extremely reactive. These elements have a lot in common in terms of properties.

Group 17 elements are known as halogens and include fluorine, chlorine, bromine, iodine, and astatine. 

This degree of closeness is not observed in other groupings of the periodic table. They exhibit a consistent gradation of physical and chemical properties. The only radioactive element in the category is astatine. They have seven electrons in their outermost shell and are one electron short of the nearest noble gas configuration. An element’s chemical characteristics and reactivity are determined by the oxidation state it exhibits.

At standard temperature and pressure, the halogen group is the only periodic table group that contains elements in three of the four primary states of matter. When halogens are linked to hydrogen, they all react to generate acids. The majority of halogens are derived from minerals or salts. As disinfectants, the middle halogens—chlorine, bromine, and iodine—are frequently utilised. The most common type of flame retardant is organobromine, but elemental halogens are hazardous and can be lethally poisonous.

Electronic Configuration of Halogens

These electrons have the electrical configuration ns2 np5 in their valence shell. As a result, these elements have 7 electrons in their outermost shell. By one electron, the element loses out on the octet configuration. As a result, these elements seek to lose one electron and make a covalent link or acquire one electron and establish an ionic bond. As a result, these are highly reactive nonmetals.

Oxidation State of Halogens

The halogen family’s elements all have a -1 oxidation state. Fluorine, the most electronegative element, only has a -1 oxidation state. Elements with +1, +3, +5, and +7 states include chlorine, bromine, and iodine. When chlorine, bromine, and iodine combine with tiny and extremely electronegative fluorine and oxygen atoms, they achieve a higher oxidation state. Chlorine and bromine oxides and oxoacids have +4 and +6 states, respectively. Because the fluorine atom lacks valence shells and d orbitals, it cannot increase its octet. 

Physical Properties of Halogens

  1. The elements in group 17 can be found in a variety of physical states. Fluorine and chlorine, for example, are gases. Bromine, on the other hand, is a liquid, whereas Iodine is solid.
  2. These elements are coloured in a number of ways. Iodine, for example, is dark violet in colour, but fluorine is pale yellow.
  3. Water dissolves Fluorine and Chlorine. Bromine and iodine, on the other hand, are very poorly soluble in water.
  4. As we progress down the group from Fluorine to Iodine, the melting and boiling temperatures of these elements increase. Fluorine, as a result, has the lowest boiling and melting points.

Chemical Properties of Halogens

  • Oxidizing Power: All halogens are excellent oxidizing agents. Fluorine is the most strong oxidising agent on the list. It has the ability to convert all halide particles to halogen. As we advance down the group, the oxidising power decreases. The halide particles also function as reducers. Their decreasing capacity, however, reduces the group as well.
  • Reaction with Hydrogen: When halogens react with hydrogen, they form acidic hydrogen halides. From HF to HI, the acidity of these hydrogen halides decreases. Fluorine reacts aggressively, and chlorine requires sunlight to function. Bromine, on the other hand, reacts when heated, whereas iodine requires a catalyst.
  • Reaction with Oxygen: Oxides are formed when halogens react with oxygen. However, it has been discovered that the oxides do not remain stable. Halogens, in addition to oxides, produce a variety of halogen oxoacids and oxoanions. Halogens are highly reactive, forming halides when they react with metals and nonmetals. As we move down the group, their reactivity decreases. Halogens have a high oxidising capacity. F2 is the most powerful oxidising halogen. It easily oxidises other halide ions in solution or in solid form. In general, a halogen oxidises a higher atomic number of halide ions. As an example:

F2 + 2X → 2F + X2 (X = Cl, Br or I)

  • The interactions of halogens with water demonstrate their relative oxidising tendency. Water is oxidised by fluorine to produce oxygen. Whereas chlorine and bromine react with water to generate hydrohalic and hypohalous acids, respectively. Iodine has a non-spontaneous reaction with water. Water in an acidic media can oxidise I. As an example:

4I (aq) + 4H+ (aq) + O2 (g) →  2I2(s) + 2H2O (l)

General Characteristics of Halogens

Atomic and Ionic Radii of Halogen Family

Group 17 members have the shortest atomic radii in their respective eras. This is due to the fact that they have the highest effective nuclear charge. Because the number of quantum shells grows from fluorine to iodine, atomic and ionic radii increase from top to bottom in a group.

Ionisation Enthalpy

Members of group 17 have almost no tendency to lose an electron. As a result, they have a very high ionisation enthalpy value. Because of the increase in atomic size, the ionisation enthalpy drops from top to bottom in the group.

Electron Gain Enthalpy

Group 17 atoms are only one electron away from achieving stable noble gas structures. As a result, at the relevant periods, these elements exhibit the highest negative electron gain enthalpy. Because of the increase in atomic size, the electron gain enthalpy of these elements gets less negative as we advance down the group. Chlorine, on the other hand, has a greater negative electron gain enthalpy than fluorine.

Electronegativity 

The elements of group 17 have a relatively high electronegativity value. Because of the drop in effective nuclear charge, electronegativity decreases along with the group. Fluorine is thus the most electronegative element.

Uses of Halogens

  1. Fluorine molecules are a significant component of toothpaste. This is because fluoride chemicals react with the enamel of the teeth, preventing tooth decay.
  2. Chlorine is mostly used as bleach. It’s also employed in the production of precious metals like platinum and gold.
  3. Because it kills bacteria on the skin, iodine is used as an antiseptic.

Interhalogen Compounds

Interhalogen compounds are those that result from the reaction of two distinct halogens. They have general compositions of XY, XY3, XY5, and XY7, where X is a bigger size halogen and Y is a smaller size halogen, and X is more electropositive than Y. As the ratio between the radii of X and Y grows, so does the number of atoms per molecule.

Biological role of Halogens

  • Fluoride anions can be present in animal ivory, bones, teeth, blood, eggs, urine, and hair. Fluoride anions may be necessary for humans in extremely small concentrations. Human blood contains 0.5 milligrammes of fluoride per litre. Fluorine levels in human bones range from 0.2 to 1.2 %. Fluorine is found in around 50 parts per billion in human tissue.
  • Chloride anions are required by many animals, including humans. The concentration of chlorine in cereals is 10 to 20 parts per million, whereas the concentration of chloride in potatoes is 0.5 %. Chloride levels in the soil that fall below 2 parts per million have a negative impact on plant growth. Human blood contains 0.3 % chlorine on average. Chlorine levels in human bone are normally around 900 parts per million. Human tissue contains between 0.2 and 0.5 % chlorine.
  • All organisms have some bromine in the form of bromide anion. Although no biological role for bromine in humans has been established, organobromine chemicals are found in several organisms. Bromine is commonly used by humans in amounts ranging from 1 to 20 mg per day. Bromine levels in human blood are normally 5 parts per million, 7 parts per million in human bones, and 7 parts per million in human tissue.
  • Humans ingest fewer than 100 micrograms of iodine each day on average. Intellectual impairment can result from an iodine deficit. Organoiodine compounds are found in human glands, particularly the thyroid gland, as well as the stomach, epidermis, and immune system. Cod, oysters, shrimp, herring, lobsters, sunflower seeds, seaweed, and mushrooms are all high in iodine. Iodine, on the other hand, is not known to play a biological role in plants.

Sample Questions

Question 1: What are interhalogen compounds?

Answer:

The chemicals generated by the reaction of two distinct halogens are known as interhalogens.

Question 2: What are the oxidation states exhibited by halogens?

Answer:

The halogen family’s elements all have a -1 oxidation state. The most electronegative element, fluorine, has only a -1 oxidation state. Chlorine, bromine, and iodine are examples of elements that have +1, +3, +5, and +7 states.

Question 3: How do halogens react with oxygen?

Answer:

Oxides are formed when halogens react with oxygen. However, the oxides have been discovered to be unstable. Halogens produce a variety of halogen oxoacids and oxoanions in addition to oxides.

Question 4: How does electron gain enthalpy of halogens compares to other groups?

Answer:

Group 17 elements’ atoms are only one electron away from achieving stable noble gas structures. As a result, at the relevant periods, these elements have the highest negative electron gain enthalpy. Due to the increase in atomic size, the electron gain enthalpy of these elements gets less negative as we advance down the group. In comparison to fluorine, however, chlorine has a lower electron gain enthalpy value.

Question 5: Are halogens good oxidizing agents?

Answer:

All of the halogens are excellent oxidizers. Fluorine is the most strong oxidising agent on the list. It has the ability to convert all halide particles to halogen.



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