Halogens are a class of chemicals. They all have one electron missing from the complete s-p octet. Because halogens are nonmetals, they accept electrons from other elements. Halogens will usually take an electron from another metal, or a weaker nonmetal. This process creates a negatively charged ion, or halogen atom. The element fluorine has the highest electronegativity, making it the most reactive of all the halogens. These elements can easily dissociate into individual atomic particles and combine with surrounding elements to form compounds. The halogens are known to be harmful to human health and are highly toxic. Each halogen has a different toxicity level (Kirk, 2012).
1.What are halogens?
Halogens are an extremely reactive group of elements found in nature. They occur in various forms as compounds with cations. These elements are found in table salt and oceans in small amounts. In elemental form, they form diatomic molecules that are linked together by a single bond. In atomic form, halogens contain one unpaired electron, which makes them easily pair up to form larger molecules (Mello, et al., 2013).
1.1. State
Halogens are chemical elements that exist in the liquid, gas, solid and ionized state. Chlorine and fluorine are both considered to be gases, but bromine is considered to be a liquids and iodine is considered to be a solids. Halogens are found in several compounds and as ions. They rarely exist in their elemental state. Most are present as halide ions. Some are minerals, such as cryolite, which is made of Na3AlF6. Other halogens are used in chemical processes.
1.2. Sources
Halogens are rarely found in pure form in nature. However, many of them have natural sources, although the sources of these have not been studied thoroughly. They are found in ocean water and in some types of marine algae, corals, sponges, and other organisms. In addition to these, halogenated compounds are found in terrestrial plants, and soil microbes.
Figure 1: Halogens
2. Elements Belonging to the Group of Halogens
Halogens are elements belonging to the 17th group of the periodic table. They each contain 7 electrons in the valence shells of their atoms. The ns2np5 arrangement describes their electronics in general. .Elements belonging to this group are Fluorine, Chlorine, Bromine, Iodine, Astatine and Tennessine (newest member of the halogen family) (Hossaini, Montzka & Feng, 2015).
2.1. Fluorine
As a result of its oxidizing and reducing properties, fluorine is one of the most reactive elements. It has been known to burn wood, asbestos, and water. When mixed with other halogens, it burns very hot and can cause fires. However, it is not a carcinogen. It is a potent irritant of the mucous membranes and eyes, and is especially damaging to the respiratory tract. Acute inhalation causes pulmonary edema and, in some cases, death. The data available at the time of this writing are relatively limited, but still provide important information. It is important to exercise extra care while working with fluorine since it is an irritation to the skin as well as the eyes. It may be treated in an area with adequate ventilation and a fume mask. It should also be monitored with a fluorine monitoring system.
2.2. Chlorine
Chlorine is the most well-known halogen element. It is a gas at room temperature, but in high concentrations, it can be toxic to humans. It can be converted to liquid form, which can be shipped or stored. Chlorine gas has a pungent odor and is yellow-green in color. It is extremely reactive and can form explosive compounds with other chemicals. Chlorine reacts readily with hydrogen. If a hydrogen atom is introduced into chlorine, it will burn with a silvery flame. Because of its affinity for hydrogen, chlorine is an excellent substitute for hydrogen in many compounds. Hydrocarbons are especially reactive with chlorine, since chlorine atoms readily add to the double and triple bonds. Chlorine molecules and chlorides contain two atoms (Cl2). Each atom has a different oxidation state, and chlorine reacts with many other elements to form chlorides.
2.3. Bromine
Bromine is a chemical element that belongs to the halogen group. The element is most commonly used in flame retardants. Most materials are flammable, and chemists have found ways to make them more resistant to fire by chemically incorporating bromine compounds into them. These compounds are known as organobromo compounds, and they can be used in a variety of organic synthesis reactions. Bromine forms mineral salts and is soluble in water and organic solvents. Compounds containing bromine may be found in the seas, where they account for about one third of the water. Bromine is highly soluble in aliphatic alcohols and carbon disulfide, and has a high bleaching capacity.
2.4. Iodine
Iodine was first discovered accidentally in 1811 by a French chemist named Bernard Courtois. He was working with his father to produce saltpetre, a component of gunpowder. The ash was collected from seaweed, which Courtois burned. Courtois then added a concentrated sulphuric acid to the mixture. The mixture produced a violet vapor, which settled on metal objects in the room. This cloud then crystallized into solid iodine. This element is now obtained from sodium iodate deposits in Bolivia. The human body uses iodine in small quantities in order to produce thyroxin, a hormone that regulates mental and physical development.
2.5. Astatine
Astatine is an element in the group of halogens and has an atomic number of 85. Its characteristics are comparable to those of other halogens, and it does not react with other substances. Astatine is a chemical element that is found in the earth’s crust. It is created by decaying radioactive elements. Its properties make it useful as a short-range radiation source. It also preferentially accumulates in the thyroid gland, allowing it to decay more rapidly than other elements in the same family. In addition, astatine emits only alpha particles, which are less likely to migrate to surrounding tissue. Astatine is an extremely rare element. In fact, there are fewer than fifty grams of astatine on earth at any given time. This makes astatine the rarest naturally-occurring element in the planet’s crust .The existence of astatine was predicted over 70 years ago, but the element was only discovered in the early twentieth century.
2.6. Ununseptium
Ununseptium is a radioactive, strong metal with the atomic number 117. Although it is not a naturally occurring element, it belongs to the group of halogens and is therefore likely to have halogen-like physical properties. However, because it is radioactive, it may pose a health risk if it comes into contact with people.
3. Main features and characteristics
Halogens are characterized by having electron configurations that are extraordinarily stable. Their valence electrons tend to donate one, allowing them to combine with other elements. They also are very reactive. Their colors vary from green to red. Iodine and astatine are almost black (Kirk, 2012).
3.1. Melting and boiling points
The melting and boiling points of halogens are related to their volatility, the strength of which decreases as the halogen group moves apart. These changes are caused by strong van der Waals forces between larger and smaller atoms. The larger halogens have more electrons than smaller ones, resulting in stronger van der Waals forces.
3.2. Bond enthalpy
The bond enthalpy between two halogens decreases with the increasing atomic radius of the halogen atom. The decrease in bond enthalpy is due to the fact that lone pairs of electrons repel each other. However, the hydrogen-fluorine bond is the strongest of all hydrogen-halogen bonds.
3.3. Compounds of halogens
Most halogens are oxidizing agents. Most halogens are found in the form of compounds or ions. As a result, they are only rarely found in elemental form. Instead, they are usually found in combinations with other elements.
4. Properties of halogens
Halogens have a melting and boiling point that increases with their atomic size. The higher the atomic size, the less volatile the element is. The significant van der Waals interactions that exist around halogen atoms are to blame for this phenomenon. These forces are also stronger in larger halogen atoms (Mello, et al., 2013).
4.1. Electronegativity
Electronegativity is a characteristic that characterizes an element’s propensity to capture an electron. It is also known as “electrostatic attraction.” It is usually measured on a scale called the Pauling scale. The higher an atom’s electronegativity is, the greater its attraction to electrons. Fluorine has the highest electronegativity among the halogens.
4.2. Solubility
Halogens are soluble in organic solvents such as hexane. This is because solvents, like halogens, have a nonpolar molecular structure. Since these two molecules are nonpolar, they are both attracted to each other by van der Waals dispersion forces. This gives halogens predictable colours in organic solutions. As far as the physical properties go, the halogens can be classified as highly reactive, toxic, and corrosive. These qualities make them excellent disinfectants but also make them dangerous chemical weapons. They need to be kept in inert receptacles for this reasons.
4.3. Chemical properties
The chemical properties of halogens show that they have different reactivity. Fluorine is the most reactive element of the group, and attacks a wide range of otherwise inert materials to form compounds. As a result, fluorine is highly toxic and dangerous. Among the halogens, iodine has the lowest reactivity, whereas bromine is chemically quite close to chlorine. Iodine reacts with metals but does not oxidize other halide ions. Iodine also reacts with starch, so it is possible to detect iodine in water by observing the colors it produces in starch.
4.3.1. Reactivity
Halogens react with many different types of metals and compounds, with the main outcome being an increase in oxidation state. These reactions may be redox or displacement reactions. In a displacement reaction, one species replaces another, and an element gains one electron. The more reactive halogen atom oxidises a less reactive halide ion, thus reducing it. As halogens move down the periodic table, they become less reactive, and bromine is much less reactive than chlorine.
4.3.2. Chemical reactions
5. Uses and applications
Halogens are naturally occurring elements with a variety of uses. They are abundant in the natural world, including in volcanoes, fumaroles, and the human body. They are also used to clean water and in the manufacturing of table salt and other chemicals. Their presence in our bodies means they are essential to our health and well-being. Today, halogens are used in a wide variety of electronics and electrical devices. They are present everywhere from the plastic that encases TVs to the printable circuit’s panels and electronic items and even battery cells (Hossaini, Montzka & Feng, 2015).
5.1. Halogen light bulbs
Halogens are used in a variety of applications, such as light bulbs. Halogen light bulbs send a current through a tungsten filament, which is surrounded by bromine or iodine gas. These light bulbs are found in most homes and offices. There are several applications for them, including under-cabinet illumination, table lamps, and floor lights. Some are even used as space heaters, which provide instant heat to a small area.
5.2. Everyday items
Halogens are also important in our everyday lives. They are found in laundry detergent. They are also in vitamins. Iodine, for example, is an essential mineral for our bodies. And bromine is used to disinfect water and clean swimming pools. However, some of the halogens should not be used without proper safety procedures .Halogens are also useful in antiseptic drugs, dyes, specialized soaps. They are important in various fields, including medicine, energy etc . They can be used for a variety of different purposes, and are extremely toxic. They can also be used to produce salts.
5.3. Energy industry and rocket fuels
Although it is a strong oxidizing and caustic gas, fluorine has several practical uses. It is used as an oxidizer of liquid rocket fuels, in the nuclear energy industry, and in manufacturing fluorides. Fluorine is also used in manufacturing toothpaste and drinking water. Fluorine compounds help prevent dental cavities. In addition to these uses, fluorine is also used in the energy industry, to produce uranium hexafluoride, a form of nuclear fuel. Fluorine is also used in high-voltage transformers as an insulating gas.
5.4. First aid kits and bleach
Halogens are essential elements that have many uses. To provide just one example, they are the basis of several common home cleaning solutions like bleach. They’re not always in their pure forms, but the elements are often used as ingredients in other products. One example is iodine, which is found in first aid kits.
5.5. Pharmaceutical industry
Iodine is also used in the pharmaceutical industry. The drug industry depends heavily on iodine, and halogens can be added to lead drugs to improve their transport properties. The metal iodide is very useful in seeding clouds in order to induce rain, and silver iodide is important for the production of photographic film. Halogens can also be added to nonpolar drugs to improve their solubility.
5.6. Production of mustard gas
Despite their versatility, halogen compounds’ toxic emissions outweigh their benefits. For example, they were used in the production of mustard gas during World War I, a deadly gas that caused suffocation and blindness in many people. Halogen compounds are also found in electronic equipment. In fact, one of the most devastating disasters in the history of telecommunications involved halogens. In the resulting fire, thousands of customers lost phone service. To fix the device system, the switch’s core component have to be updated.
5.7. Plastics and other materials
In industrial applications, halogens are used in plastics, electrical cables, and the oil and gas industries. They are used as flame retardants in plastics and other materials, as well as in the manufacturing of electronic displays. They are also used in hair-waving preparations, as well as in fire-extinguishing fluids.
Conclusion
Halogens are all non-metals and do not form double or triple bonds. For example, fluorine has no d orbitals in its valence shell, which simplifies its chemistry. Halogens, on the other hand, can expand their valence shell and hold up to 14 valence electrons. Their chemistry revolves around oxidation-reduction reactions.
Halogens are non-metals with unique chemical and physical properties. They are highly reactive and have a unique odour. Because they are non-metals, they are unstable and damaging to the environment. Some examples of halogens are bromine, fluorine, chlorine, and astatine. Halogens can also be radioactive. The ozone layer and the ecosystem can suffer greatly from their effects, so these chemicals should be avoided wherever possible.
Halogens react with water and form acidic solutions. These reactions can be explored through simple experiments. These experiments can be performed in class or used in demonstrations. These experiments can help students understand how halogens react to water. The results can be analyzed and discussed to provide a better understanding of halogen reactions.
Halogens are a class of chemical elements that have a low melting point. They also tend to have darker colors than their noble counterparts. For example, fluorine is pale yellow, green chlorine is brown/purple, and purple iodine is purple. Halogens are very strong oxidizers.
References
1. Kirk, K. L. (2012). Biochemistry of the elemental halogens and inorganic halides. Springer Science & Business Media.
2. Mello, P. A., Barin, J. S., Duarte, F. A., Bizzi, C. A., Diehl, L. O., Muller, E. I., & Flores, E. M. (2013). Analytical methods for the determination of halogens in bioanalytical sciences: a review. Analytical and Bioanalytical Chemistry, 405(24), 7615-7642.
3. Hossaini, R., Chipperfield, M. P., Montzka, S. A., Rap, A., Dhomse, S., & Feng, W. (2015). Efficiency of short-lived halogens at influencing climate through depletion of stratospheric ozone. Nature Geoscience, 8(3), 186-190.