Why halogens are highly reactive

It follows that there is a tendency for some halogenated drugs to accumulate in adipose tissue. Polyhalogenated compounds PHCs are of particular interest and importance because halogens are generally highly reactive and bioaccumulate in humans. DDT dichlorodiphenyltrichloroethane is a polyhalogenated pesticide that was banned in the United States in because of the potential harmful effects on human health. In the second half of World War II, it was used to control malaria and typhus among civilians and troops.

The US ban on DDT is cited by scientists as a major factor in the comeback of the bald eagle, the national bird of the United States, from near extinction. It is now banned in the United States because of its potential harmful effects on human health. Key: chlorine atoms: green, carbon atoms: black, hydrogen atoms: white. PHCs are generally immiscible in organic solvents or water but miscible in some hydrocarbons, from which they are often derived. PHCs are used in a vast array of products and industries, such as:.

Privacy Policy. Skip to main content. Nonmetallic Elements. Search for:. Halogens Properties of the Halogens Halogens fluorine, chlorine, bromine, iodine, astatine are nonmetal elements that are highly electronegative and reactive. Learning Objectives Describe the physical and chemical properties of halogens. Down the group, atom size increases. As a diatomic molecule, fluorine has the weakest bond due to repulsion between electrons of the small atoms.

Due to increased strength of Van der Waals forces down the group, the boiling points of halogens increase. Therefore, the physical state of the elements down the group changes from gaseous fluorine to solid iodine.

Due to their high effective nuclear charge, halogens are highly electronegative. Therefore, they are highly reactive and can gain an electron through reaction with other elements. Halogens can be harmful or lethal to biological organisms in sufficient quantities. Key Terms electronegativity : The tendency of an atom to attract electrons to itself.

They share similar chemical properties. Halogen Compounds Halogens are highly reactive and can form hydrogen halides, metal halides, organic halides, interhalogens, and polyhalogenated compounds. Learning Objectives Discuss halogen compounds and their properties. Key Takeaways Key Points Hydrogen halides are binary compounds of halogens with hydrogen. They are strong hydrohalic acids when dissolved in water, with the exception of HF.

All of these acids are dangerous; some are widely used in chemical manufacturing plants. Metal halides are compounds of halogens and metals. They include highly ionic compounds, monomeric covalent compounds, and polymeric covalent compounds. Metal halides can be obtained through direct combination or through neutralization of a basic metal salt with a hydrohalic acid.

Interhalogen compounds are formed when halogens react with each other. Some resemble the pure halogens in some respects, but mostly their properties and behaviors are intermediates of those of the two parent halogens.

Halogenated compounds, or organic halides, are organic compounds that contain halogen atoms. In the human body, some halogens perform multiple regulatory functions, while others are not essential. Organohalogens are synthesized through the nucleophilic abstraction reaction.

Compounds substituted with multiple halogens are known as polyhalogenated compounds. Many of them are very toxic and bioaccumulate in humans, but they have many potential applications. Key Terms interhalogen : A binary compound of two different halogens.

Learning Objectives Discuss the uses of various halogens. Key Takeaways Key Points Fluoride can be found in many everyday products, including toothpaste, vitamin supplements, baby formulas, and even public water. However, overconsumption of fluoride can be fatal. Astatine - Astatine is a radioactive element with an atomic number of 85 and symbol At.

It is the only halogen that is not a diatomic molecule and it appears as a black, metallic solid at room temperature. Astatine is a very rare element, so there is not that much known about this element. In addition, astatine has a very short radioactive half-life , no longer than a couple of hours. It was discovered in by synthesis.

Also, it is thought that astatine is similar to iodine. However, these two elements are assumed to differ by their metallic character.

The periodic trends observed in the halogen group:. The melting and boiling points increase down the group because of the van der Waals forces. The size of the molecules increases down the group. This increase in size means an increase in the strength of the van der Waals forces.

In addition, more energy levels are added with each period. This results in a larger orbital, and therefore a longer atomic radius. If the outer valence electrons are not near the nucleus, it does not take as much energy to remove them. Therefore, the energy required to pull off the outermost electron is not as high for the elements at the bottom of the group since there are more energy levels.

Also, the high ionization energy makes the element appear non-metallic. The number of valence electrons in an atom increases down the group due to the increase in energy levels at progressively lower levels. The electrons are progressively further from the nucleus; therefore, the nucleus and the electrons are not as attracted to each other.

An increase in shielding is observed. An electron will not be as 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. This is due to the fact that atomic radius increases in size with an increase of electronic energy levels. This lessens the attraction for valence electrons of other atoms, decreasing reactivity. This decrease also occurs because electronegativity decreases down a group; therefore, there is less electron "pulling.

A halide is formed when a halogen reacts with another, less electronegative element to form a binary compound. Hydrogen, for example, reacts with halogens to form halides of the form HX:. Hydrogen halides readily dissolve in water to form hydrohalic hydrofluoric , hydrochloric , hydrobromic , hydroiodic acids. The properties of these acids are given below:. It may seem counterintuitive to say that HF is the weakest hydrohalic acid because fluorine has the highest electronegativity.

A strong bond is determined by a short bond length and a large bond dissociation energy. Of all the hydrogen halides, HF has the shortest bond length and largest bond dissociation energy.

A halogen oxoacid is an acid with hydrogen, oxygen, and halogen atoms. The acidity of an oxoacid can be determined through analysis of the compound's structure. The halogen oxoacids are given below:. In each of these acids, the proton is bonded to an oxygen atom; therefore, comparing proton bond lengths is not useful in this case.

Instead, electronegativity is the dominant factor in the oxoacid's acidity. Acidic strength increases with more oxygen atoms bound to the central atom. The halogens' colors are results of the absorption of visible light by the molecules, which causes electronic excitation.

Fluorine absorbs violet light, and therefore appears light yellow. Iodine, on the other hand, absorbs yellow light and appears violet yellow and violet are complementary colors, which can be determined using a color wheel. The colors of the halogens grow darker down the group:. In closed containers, liquid bromine and solid iodine are in equilibrium with their vapors, which can often be seen as colored gases.

Although the color for astatine is unknown, it is assumed that astatine must be darker than iodine's violet i. As a general rule, halogens usually have an oxidation state of However, if the halogen is bonded to oxygen or to another halogen, it can adopt 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 adopts the -1 oxidation state.

Chlorine is more electronegative than iodine, therefore giving it the -1 oxidation state. Adding both of these values together, the total oxidation state of the compound so far is One third exception to the rule is this: if a halogen exists in its elemental form X 2 , its oxidation state is zero. Electronegativity increases across a period, and decreases down a group. Therefore, fluorine has the highest electronegativity of all of the elements, indicated by its position on the periodic table.

If fluorine gains one more electron, the outermost p orbitals are completely filled resulting in a full octet. Because fluorine has a high electronegativity, it can easily remove the desired electron from a nearby atom. Fluorine is then isoelectronic with a noble gas with eight valence electrons ; all its outermost orbitals are filled. Fluorine is much more stable in this state. Fluorine : Although fluorine is very reactive, it serves many industrial purposes. For example, it is a key component of the plastic polytetrafluoroethylene called Teflon-TFE by the DuPont company 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 possible environmental impact led to their discontinued use. Hydrochlorofluorocarbons HFCs are now used instead. Fluoride is also added to toothpaste and drinking water to help reduce tooth decay. Fluorine also exists in the clay used in some ceramics.

Fluorine is associated with generating nuclear power as well. In addition, it is used to produce fluoroquinolones, which are antibiotics. Solution : Halogens are very reactive due to low bond dissociation energies of the molecule and high electron affinities of their atoms.

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