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. The neutralized form of hydrochloride is a component of many medications.
Chlorine is also used to sterilize hospital machinery and limit infection growth. This is one electron away from having a full octet of eight electrons, so these elements tend to form anions having -1 charges, known as halides : fluoride, F - ; chloride, Cl - , bromide, Br - , and iodide, I -. In combination with other nonmetals, the halogens form compounds through covalent bonding.
In their elemental form, the halogens form diatomic molecules, X 2 , connected by single bonds. Since all of the halogens have one unpaired electron in their atomic forms, it is easy for them to "pair up" to form diatomic molecules. The halogens are extremely reactive especially fluorine , and are not found naturally in their elemental forms. They are usually found in combination with various metals in minerals, or in combination with other nonmetals in molecular compounds.
The halogens also form compounds with carbon easily; organic molecules containing carbon are often known as alkyl halides , or organohalides , and have many different household and industrial uses. In combination with hydrogen which also has one unpaired electron , the halogens form the hydrohalic acids : hydrofluoric acid HF , hydrochloric acid HCl , hydrobromic acid HBr , and hydroiodic acid HI.
In its elemental form, fluorine F 2 is a pale yellow gas; it is extremely reactive and toxic. In fact, a large number of chemists who tried to isolate elemental fluorine — which turned out to be an extremely difficult task — died at relatively early ages.
The name of the element is derived from Latin word fluere , which means "to flow. In its ionic form, fluoride F - , it essential in the diet, but only in small doses. Fluoride is used in toothpaste, and is often added to municipal drinking water, at concentrations at or below 1 ppm, to protect against tooth decay. At least in small doses, it has no effect on anyone's " precious bodily fluids. Fluorine atoms form very strong bonds to carbon atoms, so fluorine is incorporated into many organic molecules, including the chlorofluorocarbons, which contain carbon, chlorine, and fluorine, which were widely used as propellants and refrigerants until their ozone-destroying properties were discovered see entry on Freon in the Alkanes section of the Molecule Gallery , and also in Teflon see entry on Teflon in the Polymers section of the Molecule Gallery.
Fluorine is also found in hydrogen fluoride, or hydrofluoric acid, HF, a weak acid. It is used in etching glass, cleaning stainless steel, and in processing uranium ore.
In the processing of uranium, uranium in the ore is transformed into uranium hexafluoride, UF 6 , which can be sublimed into the gas phase; in this form, fissionable uranium isotopes can be separated from non-fissionable uranium isotopes by gas diffusion. Hydrofluoric acid is toxic and corrosive, and eats through glass it must be stored in plastic bottles ; it penetrates the skin quickly, and causes intense pain. Concentrated solution can also start reactions with calcium ions in the body, causing hypocalcemia an electrolyte disturbance resulting from loss of calcium , cardiac arrest, or death.
The halogens are the only periodic table group containing elements in all three familiar states of matter solid, liquid, and gas at standard temperature and pressure. 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. These include highly ionic compounds such as sodium chloride, monomeric covalent compounds such as uranium hexafluoride, and polymeric covalent compounds such as palladium chloride.
Metal halides are generally obtained through direct combination or, more commonly, through neutralization of a basic metal salt with a hydrohalic acid. Silver Chloride : Silver chloride is the precipitate formed when silver nitrate solution is added to chloride solution.
The halogens react with each other to form interhalogen compounds. The properties and behavior of a diatomic interhalogen compound tend to be intermediates of those of its parent halogens. Some properties, however, are found in neither parent halogen. Many synthetic organic compounds, such as plastic polymers, as well as a few natural organic compounds, contain halogen atoms; these are known as halogenated compounds, or organic halides.
Chlorine is by far the most abundant of the halogens and is the only one needed as chloride ions in relatively large amounts by humans. For example, chloride ions play a key role in brain function by mediating the action of the inhibitory transmitter GABA. They are also used by the body to produce stomach acid.
0コメント