Why melting point increases in group 7

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.

Boundless vets and curates high-quality, openly licensed content from around the Internet. This particular resource used the following sources:. All the halogens exist as diatomic molecules—F 2 , Cl 2 , and so on. Larger molecules farther down the group have more electrons which can move around and form the temporary dipoles that create these forces.

The stronger intermolecular attractions down the group require more heat energy for melting or vaporizing, increasing their melting or boiling points. Fluorine reacts violently with water to produce aqueous or gaseous hydrogen fluoride and a mixture of oxygen and ozone; its solubility is meaningless.

Chlorine, bromine and iodine all dissolve in water to some extent, but there is again no discernible pattern. Chlorine dissolved in water produces a pale green solution. Bromine solution adopts a range of colors from yellow to dark orange-red depending on the concentration. Iodine solution in water is very pale brown. Chlorine reacts with water to some extent, producing a mixture of hydrochloric acid and chloric I acid also known as hypochlorous acid.

The reaction is reversible, and at any time only about a third of the chlorine molecules have reacted.

Chloric I acid is sometimes symbolized as HOCl, indicating the actual pattern bonding pattern. Bromine and iodine form similar compounds, but to a lesser extent. In both cases, about Although iodine is only slightly soluble in water, it dissolves freely in potassium iodide solution, forming a dark red-brown solution. A reversible reaction between iodine molecules and iodide ions gives I 3 - ions. These are responsible for the color. In the laboratory, iodine is often produced through oxidation of iodide ions.

As long as there are any excess iodide ions present, the iodine reacts to form I 3 -. Once the iodide ions have all reacted, the iodine is precipitated as a dark gray solid.

The halogens are much more soluble in organic solvents such as hexane than they are in water. Both hexane and the halogens are non-polar molecules, so the only intermolecular forces between them are van der Waals dispersion forces.

Because of this, the attractions broken between hexane molecules and between halogen molecules are similar to the new attractions made when the two substances mix.

Organic solutions of iodine are pink-purple in color. Bond enthalpy is the heat required to break one mole of covalent bonds to produce individual atoms, starting from the original substance in the gas state, and ending with gaseous atoms. For chlorine, Cl 2 g , it is the heat energy required for the following reaction, per mole:. Although bromine is a liquid, the bond enthalpy is defined in terms of gaseous bromine molecules and atoms, as shown below:.

Covalent bonding is effective because the bonding pair is attracted to both the nuclei at either side of it. It is that attraction which holds the molecule together. The extent of the attraction depends in part on the distances between the bonding pair and the two nuclei. The figure below illustrates such a covalent bond:.

As the atoms get larger down the group, the bonding pair is further from the nuclei and the strength of the bond should, in theory, decrease, as indicated in the figure below. The question is whether experimental data matches this prediction.

Because fluorine atoms are so small, a strong bond is expected—in fact, it is remarkably weak. 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.

Below is a list of some of fluorine's important inorganic compounds. Chlorine : Chlorine has many industrial uses. It is used to disinfect drinking water and swimming pools. Sodium hypochlorite NaClO is the main component of bleach. Hydrochloric acid, sometimes called muriatic acid, is a commonly used acid in industry and laboratories. Chlorine is also present in polyvinyl chloride PVC , and several other polymers. PVC is used in wire insulation, pipes, and electronics. In addition, chlorine is very useful in the pharmaceutical industry.

Medicinal products containing chlorine are used to treat infections, allergies, and diabetes.