Halogens of The Periodic Table
Halogens elements located in group seventeen of the periodic table. Halogen word is coming from Greek word Hal (salt) and gen (to produce) because they all produce sodium salts of similar properties. They are Fluorine (F), Chlorine (Cl), Bromine (Br), Iodine (I), Astatine (As) and Tennessine (Ts). In this topic we will study about the halogens and their properties.
Halogens are toxic in their elemental form, although their compounds have many uses in daily life. All halogens have seven electrons in their outer shell and can accept one electron to form an ion with a –1 charge. When we moving down the group atomic radii will be increase. They are also known as p-block elements. They are not found free in nature because of their high reactivity. Now we will discuss about their occurrence, properties or their daily life uses.
Occurrence: Fluorine is the most abundant halogen in the earth’s crust. The ratio of halogens in the igneous rocks of the earth’s crust is 0.06 Fluorine, 0.031 Chlorine, 0.00016 Bromine, 0.0003 Iodine. Astatine and tennessine do not occur in nature because they are only short-lived radioactive isotopes. Tennessine is purely man-made and has no other roles in nature.
Properties of Halogen
Physical Properties of Halogens
- Halogens are highly reactive in nature thus, they do not found freely in nature.
- Their melting and boiling points are increases as wo go down the group.
- Their Density is also increase.
- Fluorine and chlorine are gases while bromine is found in liquid form at room temperature or iodine and astatine are solids.
- All halogens are colored. Fluorine is a very pale green gas, chlorine is greenish yellow in color while bromine is a reddish-brown liquid or iodine is a grey solid that sublimes to a purple vapor. And astatine is the black solid and radioactive.
- Ionization enthalpy and electronegativity will be decrease as we go down the group.
- They are volatile or poisonous in nature.
- All elements of this group exist as diatomic molecules.
- Halogens have large negative Electron gain enthalpy.
- Halogens show two types of oxidations state that is negative and positive.
- Due to high ionization enthalpy and high electronegativity, all halogens are non-metallic in nature. The non-metallic character decreases down the group from fluorine to iodine.
Chemical Properties of Halogens
- As we moving down the group, reactivity of the halogens decreases so, the more reactive halogen will always displace a less reactive halogen in a compound.
- The chemical activity of halogen atoms depends both on their point of attachment to lead and on the nature of the halogen.
- These displacement reactions using aqueous solutions of potassium chloride (KCl). When we add chlorine water to an aqueous solution of potassium chloride. No reaction would happen. Since chlorine is more reactive than bromine. Chlorine will displace in potassium bromide (KBr) producing potassium chloride and liberating bromine. Cl2 + 2KBr → 2KCl + Br2
- Halogens can react with certain metals to form metal halides. For example- sodium chloride or table salt. Sodium chloride (NaCl) is extracted from the sea or form salt mines.
- Halogens can react with hydrogen gas to produce the corresponding hydrogen halide. Most of these reactions are highly exothermic. As an example, chlorine gas and hydrogen gas can react to form hydrogen chloride (HCl). H2 + Cl2 → 2HCl
- Halogens forms binary compounds with oxygen. For example- OF2, Br2O etc.
- Halogens react with each other to form a number of compounds called interhalogen compounds.
- Poly halogens are compounds that are synthetically synthesized and replaced by Poly halogens. Many of them are highly toxic and Bio accumulative to humans and have a wide range of uses. These include polychlorinated biphenyls (C12H10-XClX-), polybrominated diphenyl ethers (PBDEs), and per fluorinated compounds (PFCs), as well as many other compounds.
Reactions of Halogens
(1) 2F2(g) + 2 H2O(l) → O2(g) + 4 HF (aq)
(2) Cl2(g) + H2O(l) → HCl(aq) + HClO (aq)
(3) Br2(g) + H2O(l) → HBr(aq) + HBrO (aq)
Uses of Halogens
Uses of Fluorine
- Fluorine is used in toothpastes, hydrofluoric acid (HF), mineral water.
- Freon is useful for cooling in freezers, refrigerators and air conditioners. It is harmful because it causes depletion of ozone layer (ozone hole).
- Fluoride anions are found in dentin, bones, teeth, blood, eggs, urine and hair of living organisms. Fluoride anions can be necessary for humans in very small quantities.
Uses of Chlorine
- Chlorine gas are useful in getting clean water. Chlorine is a disinfectant and is added to water purification systems to eliminate bacteria and other microorganisms.
- Table salt NaCl.
- Bleaching powder of clothes.
- Dry battery NH4
- Chloroform CHCl3.
- Plastic PVC.
- Hydrochloric acid HCl.
Uses of Bromine
- In photographic films as Silver Bromide (AgBr).
- In Lipstick.
- In all living things, some bromine occurs in the form of bromide anions. The biological role of bromine in humans is not clear, but some organisms contain Organobromine compounds.
- In hydro bromic acid HBr.
Uses of Iodine
- Iodine is used to make a purple-colored solution called tincture of iodine which is applied on cuts and wounds as an antiseptic.
- It is added to table salt, to treat thyroid gland disease, Such as goiter.
- It is used In Hydroiodic acid (HI).
Halogens Interesting Facts
- Fluoride is one of the most reactive elements.
- Simple halogen-containing compounds are called halides.
- Fluorine gas is deadly, Inhaling air with a concentration of less than 0.1% fluorine can be cause of death.
- A small amount of fluoride in water and toothpaste is used to prevent tooth decay.
- The first halogen was isolated and identified as the chlorine element.
- Astatine have found uses in medicine, even if they are radioactive and break down quickly.
- The bromine liquid evaporates easily at room temperature and gives off orange vapor. Bromine has a very strong and bad odor. Its name is derived from the Greek word “bromos”, which means “smell”.
- Despite the toxicity of fluoride and chlorine, small amounts are essential to human health and life. Iodine is also essential for human health.
We have discussed above about halogens and their physical and chemical properties. We have also discussed about their daily life uses and some interesting facts related to it. Now I hope you get all the information about this topic.