Halogens diatomic molecules formed

Lewis and many other chemists had recognized the shortcomings of the ionic bond. When diatomic molecules, such as or Cl, were considered, there was no reason why one atom should lose an electron and an identical atom should gain an electron. There had to be another explanation for how diatomic molecules formed. We have seen how the octet rule applies to the formation of ionic compounds by the transfer of electrons. This rule also helps explain the formation of covalent bonds when molecules (covalent compounds) form. Covalent bonds result when atoms share electrons. Using fluorine, F, as a representative halogen, we can see how the octet rule applies to the formation of the molecule. Each fluorine atom has seven valence electrons and needs one more electron to achieve the stable octet valence configuration. If two fluorines share a pair of electrons, then the stable octet configuration is achieved ... 

Table 8.1. Atomic charges in the 21 heteronuclear diatomic molecules formed hy comhination of H, the alkali metal Li, Na or K, and the halogen F, Cl or Br atoms experimental and calculated ionic characters, q Q atomic charges calculated by natural atomic orbital (NAO) analysis, and by topological analysis of the electron densities (AIM) [2]. All charges in atomic units. Note that the chemical formulae have been written in such a way that the atom carrying net positive charge is listed first.

Table 6-VI lists some properties of the halogens. In the elemental state, the halogens form stable diatomic molecules. This stability is indicated by the fact that it takes extremely high temperatures to disrupt halogen molecules to form the monatomic species. For example, it is known that the chlorine near the surface of the sun, at a temperature near 6000°C, is present as a gas consisting of single chlorine atoms. At more normal temperatures, chlorine atoms react with each other to form molecules ...

The first column of the periodic table, Group 1, contains elements that are soft, shiny solids. These alkali metals include lithium, sodium, potassium, mbidium, and cesium. At the other end of the table, fluorine, chlorine, bromine, iodine, and astatine appear in the next-to-last column. These are the halogens, or Group 17 elements. These four elements exist as diatomic molecules, so their formulas have the form X2 A sample of chlorine appears in Figure EV. Each alkali metal combines with any of the halogens in a 1 1 ratio to form a white crystalline solid. The general formula of these compounds s, AX, where A represents the alkali metal and X represents the halogen A X = N a C 1, LiBr, CsBr, KI, etc.). 

A shared pair of electrons creates a single covalent bond in F. Often the double dots forming the bond are replaced with a short dash to represent the bond (F-F). The other halogens form diatomic molecules with single bonds in a similar fashion. 

In vapor state, gold is formed by diatomic molecules (Au2), whose dissociation energy is higher than those of many other diatomic non-metal elements, such as halogens.3... 

The diatomic molecules which show hindered rotation in the solid generally have quite complicated molecular crystals. This is true, for instance, of the halogens. CI2 forms a crystal composed of molecules, each of interatomic distance 1.82 A (compared to 1.98 A in the gas), arranged in a complicated way which we shall not describe. Iodine I2 forms a layer lattice. In Fig. XXIV-3 we show one of the layers, showing... 

The value of the periodic system is clearly illustrated by the halogens. All four of the elementary substances form diatomic molecules X2 their hydrogen compounds all have the formula HX, and their sodium salts the formula NaX. The free elements are all oxidizing agents, and their oxidizing power decreases regularly in the order Fg, CI2, Brg, I2. 

The elements that tend to exist as diatomic molecules are hydrogen, oxygen, nitrogen, and the halogens. Typically, when these elements are discussed, it is assumed that they are in their diatomic form unless otherwise stated. In other words, the statement "Nitrogen is nonreactive." refers to N2 and not N. 

The halogens are univalent. They form the diatomic molecules F2, Cl2, Br2, I2, and At2. The first four of these molecules are represented in the drawing. 

For elements which form diatomic molecules A2 with single bonds, Da-a is equal to the energy of dissociation. This applies to H2, the halogens, the alkali metals, silver and copper. A few other elements form homoatomic molecules A . In the P4—AS4—and Sb4-molecules, for instance, each element is bonded to three other atoms, as in compounds of type AB3. As there are six A—A bonds in the A4-molecules, the bond energy Da-a is one sixth of the energy of dissociation for the reaction... 

In many cases, element B will exist as a diatomic molecule in its standard state (e.g. the halogens). To include it in the cycle the element must be dissociated to form monoatomic atoms, as in stage C ... 

The halogens are electronegative and oxidizing elements, fluorine exceptionally so. They occur in nature as halides, and form highly reactive diatomic molecules. Molecular halides are formed with most nonmetals, ionic halides with metals. Some halides are good Lewis acids, and many halide complexes are known. 

For nonmetals there is no single rule. Carbon, for example, exists as an extensive three-dimensional network of atoms, and so we use its empirical formula (C) to represent elemental carbon in chemical eqnations. Bnt hydrogen, nitrogen, oxygen, and the halogens exist as diatomic molecules, and so we use their molecular formulas (H2, N2, O2, F2, CI2, Br2,12) in equations. The stable form of phosphorus is molecular (P4), and so we use P4. For sulfur chemists often nse the empirical formula (S) in chemical equations, rather than Sg which is the stable form. Thus, instead of writing the equation for the combnstion of sulfur as... 

The halogens form a very large number of compounds. In the elemental state they form diatomic molecules, X2. In nature, however, because of their high reactivity, halogens are always found combined with other elements. Chlorine, bromine, and iodine occur as halides in seawater, and fluorine occurs in the minerals fluorite (CaF2) (see Figure 20.18) and cryolite (Na3AlF6). 

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). 

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