This characteristic makes them more reactive than other non-metal groups. Group Physical Properties of the Halogens It can be seen that there is a regular increase in many of the properties of the halogens proceeding down group 17 from fluorine to iodine. This includes their melting points, boiling points, intensity of their color, the radius of the corresponding halide ion, and the density of the element.
On the other hand, there is a regular decrease in the first ionization energy as we go down this group. As a result, there is a regular increase in the ability to form high oxidation states. Includes trends in atomic and physical properties, the redox properties of the halogens and their ions, the acidity of the hydrogen halides, and the tests for the halide ions.
Its atomic number is 9 and its atomic weight is 19, and it's a gas at room temperature. Depending on who you ask, there are either 5 or 6 halogens. Fluorine, chlorine, bromine, iodine, and astatine definitely are halogens. Element , tennessine, might have some properties in common with the other elements.
Even though it is in the same column or group of the periodic table with the other halogens, most scientists believe element behaves more like a metalloid. So little of it has been produced, it's a matter of prediction, not empirical data. These elements share some common properties that distinguish them from other elements on the periodic table.
The lighter halogens occur in living organisms. These are fluorine, chlorine, bromine, and iodine. Of these, chlorine and iodine are essential for human nutrition, although the other elements might also be required in trace amounts.
The halogens are important disinfectants. Chlorine and bromine are used to disinfect water an surfaces. Their high reactivity also makes these elements important components of some types of bleach. Halogens are used in incandescent lamps to make them glow at a higher temperature and with a white color. The halogen elements are important drug components, as they aid drug penetration into tissues. Physical States of Halogens : Halogens represents all of the three familiar states of matter: left to right chlorine is a gas, bromine is a liquid, and iodine is a solid.
Highly reactive fluorine is not included in the picture. Electronegativity is the ability of an atom to attract electrons or electron density towards itself within a covalent bond. Electronegativity depends upon the attraction between the nucleus and bonding electrons in the outer shell. This, in turn, depends on the balance between the number of protons in the nucleus, the distance between the nucleus and bonding electrons, and the shielding effect of inner electrons. In hydrogen halides HX, where X is the halogen , the H-X bond gets longer as the halogen atoms get larger.
This means the shared electrons are further from the halogen nucleus, which increases the shielding of inner electrons. This means electronegativity decreases down the group. Halogens are highly reactive, and they can be harmful or lethal to biological organisms in sufficient quantities.
This reactivity is due to high electronegativity and high effective nuclear charge. Halogens can gain an electron by reacting with atoms of other elements. Fluorine is one of the most reactive elements. It reacts with otherwise inert materials such as glass, and it forms compounds with the heavier noble gases. It is a corrosive and highly toxic gas. Fluorine can react with glass in the presence of small amounts of water to form silicon tetrafluoride SiF4.
Thus fluorine must be handled with substances like the inert organofluorine compound Teflon. Chlorine has maximum solubility of 7. Dissolved chlorine reacts to form hydrochloric acid HCl and hypochlorous acid HClO , a solution that can be used as a disinfectant or bleach:.
Bromine has a solubility of 3. Iodine is minimally soluble in water, with a solubility of 0. However, iodine will form an aqueous solution in the presence of iodide ion. This occurs with the addition of potassium iodide KI , forming a triiodide ion. Halogens are highly reactive and can form hydrogen halides, metal halides, organic halides, interhalogens, and polyhalogenated compounds. The halogens all form binary compounds with hydrogen, and these compounds are known as the hydrogen halides: hydrogen fluoride HF , hydrogen chloride HCl , hydrogen bromide HBr , hydrogen iodide HI , and hydrogen astatide HAt.
All of these except HF are strong chemical acids when dissolved in water. However, hydrofluoric acid does have quite destructive properties towards animal tissue, including that of humans. When in aqueous solution, the hydrogen halides are known as hydrohalic acids. The names of these acids are as follows:.
All of these acids are dangerous and must be handled with great care. Some of these acids are also widely used in chemical manufacturing plants. Hydrogen astatide should also be a strong acid hydroastatic acid , but it is seldom included in presentations about hydrohalic acids because of the extreme radioactivity of astatine via alpha decay and the fact that it readily decomposes into its constituent elements hydrogen and astatine.
The halogens form many compounds with metals. Bromine consists of bromide salts, which have been found in the sea. The world production of bromide has increased significantly over the years, due to its access and longer existence. Like all of the other halogens, bromine is an oxidizing agent, and is very toxic.
Iodine - Iodine has the atomic number 53 and symbol I. Iodine exists as a diatomic molecule, I 2 , in its elemental state. At room temperature, it appears as a violet solid. Iodine has one stable isotope: I. It was first discovered in through the use of seaweed and sulfuric acid. Currently, iodide ions can be isolated in seawater. Although iodine is not very soluble in water, the solubility may increase if particular iodides are mixed in the solution. Iodine has many important roles in life, including thyroid hormone production.
This will be discussed in Part VI of the text. 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:.
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