THE HALOGENS GROUP 7A

The Group 7A elements fluorine, chlorine, bromine, iodine, and astatine are known collectively as the halogens, meaning salt producers. The name was first applied to chlorine because of its ability to combine with metals to form salts. All but the extremely rare and poorly characterized astatine are now known to have this same ability. Although there is the usual variation in group properties, the striking similarities among these elements are reminiscent of those of the alkali and alkaline-earth metals. 

After the usual sections on the history of the discoveries of and the application of the network to the halogens, special sections on (1) the oxoacids and their salts and (2) the interhalogens follow. The section on reactions and compounds of practical importance comes next and finally the selected topic in depth, which concerns the threat posed by chlorofluorocarbons to the ozone layer. 

Some of the properties of the group 7A elements, the halogens, are given in Table 7.7. Astatine, which is both extremely rare and radioactive, is omitted because many of its properties are not yet known. 

Element Electron Configuration Melting Point (°C) Density Atomic Radius (A) (Hl/mol) 

The halogens do not exist as Xg molecules like sulfur and selenium do. Can you specuiate why  

Why are more molecules of I2 seen in the molecular view relative to the number of CI2 molecules  

As a result, fluorine gas is difficult and dangerous to use in the laboratory, requiring 

Unlike the group 6A elements, all the halogens are typical nonmetals. Their melting and boiling points increase with increasing atomic number. Fluorine and chlorine are gases at room temperature, bromine is a liquid, and iodine is a solid. Each element consists of diatomic molecules E2, CI2, Br2, and I2 ( FIGURE 7.27). 

Our last chance to view very active elements occurs in Group 7A(17). The halogens begin with fl uorine (F), the strongest electron grabber of all. Chlorine (Cl), bromine (Br), and iodine (I) also form compounds with most elements, and even rare astatine (At) is thought to be reactive [Group 7A(17) Family Portrait, p. 448]. 

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Solution (a) I Iodine (53I) is in Group 7A(17), the halogens. Like any member of this group, it gains 1 electron to attain the same numba" as the nearest Group 8A(18) member, in this case, 54Xe. 

Elements in Group 1A (1) are called the alkali metals, Group 2 A (2), the alkaline earth metals Group 7A (17), the halogens and Group 8A (18), the noble gases. 

The activity series of the halogens. Reactivity decreases down Group 7A(17), so we can arrange the halogens into their own activity series ... 

In Group 7A(17), fluorine and chlorine have the condensed electron configuration [noble gas] ns np, as do the other halogens (Br, I, At). Little is known about rare, radioactive astatine (At), but all the others are reactive nonmetals that occur as diatomic molecules, X2 (where X represents the halogen). All form ionic compounds with metals (KX, MgX2), covalent compounds with hydrogen (HX) that yield acidic solutions in water, and covalent compounds with carbon (CX4). 

When a halogen atom [Group 7A(17)] adds a single electron to the five in its np sublevel, it becomes isoelectronic with the next noble gas. Bromide ion, for example, is isoelectronic with krypton (Kr) ... 

The Group 7A(17) elements form many ionic and covalent compounds metal and nonmetal halides, halogen oxides, and oxoacids. Like the alkali metals, the halogens have an electron configuration one electron away from that of a noble gas whereas a 1A metal atom must lose one electron, a 7A nonmetal atom must gain one. It fills its outer level in either of two ways ... 

Halogen Oxides, Oxoacids, and Oxoanions The Group 7A(17) elements form many oxides that are powerful oxidizing agents. Dichlorine monoxide (CI2O), chlorine dioxide (CIO2, with an unpaired electron and Cl in the unusual -t-4 oxidation state), and dichlorine heptaoxide (CLOy) are important examples. 

Figure 14,19 Standing in Group 8A(18), looking backward at the halogens, Group 7A(17), and ahead to the alkali metals, Group 1A(1).

Discuss key features of Group 7A(17), understand how inter-molecular forces and the ns np configuration account for physical and chemical properties, and describe the halogen oxides and oxoacids ( 14.8) (EPs 14.68-14.75)... 

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