Nonmetal diatomic molecules

The terms AHAm and AHAy are the enthalpies of atomization of the metal and the nonmetal, respectively. For gaseous diatomic nonmetals, AHA is the enthalpy of dissociation (bond energy plus RT) of the diatomic molecule. For metals which vaporize to form monatomic gases, AHA is identical to the enthalpy of sublimation. If sublimation occurs to a diatomic molecule, M2> then the dissociation enthalpy of the reaction must also he included ... 

Some other free (uncombined) elements also occur in different forms. Different forms of the same element are called allotropes of each other. Except for oxygen, the elements that form diatomic molecules when uncombined do not form allotropes, but many other nonmetals do. The allotropes of carbon— diamond and graphite—are perhaps best known to the general public. Sulfur and phosphorus are also notable for forming allotropes. 

Although the gas-phase dissociative X-O bond energies (AHdbe) are known for many diatomic and nonmetal-lic molecules (see Table 5 for illustrative examples)/ the metal-oxygen bond energetics for transition-metal complexes, organometallics, and metalloproteins in the condensed phase are not understood. With the latter systems, the traditional thermochemical methods of evaluation are tedious and imprecise. 

The radius of a nonmetal atom is often determined from a diatomic molecule of an element. 

Explain why the gaseons nonmetals exist as diatomic molecules, but other gaseous elements exist as single atoms. (Chapter 9)... 

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. 

Seven elements, all of them nonmetals, do not exist as individual atoms in their pure form. Rather, for reasons you will learn later (see The Diatomic Elements table below), two (sometimes more) atoms join together to form a molecule, a particle composed of two or more atoms bonded together. These seven elements exist as diatomic molecules (di-meaning two, -atomic meaning atom), and are listed in the following table. 

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... 

A sample of hydrogen gas consists of these diatomic molecules (H2)—pairs of atoms that are chemically bound and behave as an independent unit—not separate H atoms. Other nonmetals that exist as diatomic molecules at room temperature are nitrogen (N2), oxygen (O2), and the halogens [fluorine (F2), chlorine (CI2), bromine (Br2), and iodine (E)]. Phosphorus exists as tetratomic molecules (P4), and sulfur and selenium as octatomic molecules (Sg and Scg) (Figure 2.14). At room temperature, covalent substances may be gases, liquids, or solids. 

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). 

I Diatomic molecules that are formed from two different types of nonmetal atoms generally form ... 

For metals such as sodium, the atomic radius is defined as half the distance between adjacent nuclei in a crystal of the element as shown in Figure 6.10. For elements that commonly occur as molecules, such as many nonmetals, the atomic radius is defined as half the distance between nuclei of identical atoms that are chemically bonded together. The atomic radius of a nonmetal diatomic hydrogen molecule (H2) is shown in Figure 6.10. 

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). 

The halogens (group 7A) are nonmetals that exist as diatomic molecules. The halogens have the most negative electron affinities of the elements. Thus, their chemistry is dominated by a tendency to form 1— ions, especially in reactions with metals. 

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