Electronegativity nonmetals

The most reactive nonmetals (electronegative) are those in group 17 (VIIA) on the right side of the table. (See exception noted in rule 19c.) They tend to accept valence electrons from the metals to complete their outer valence shells from seven electrons to form full outer shells of eight electrons. 

Nonmetals Electronegative elements that are neither ductile, malleable, or good conductors of electricity. 

These trends are general ones, observed with other oxoadds of the nonmetals. Recall, for example, that nitric acid, HNO3 (oxid. no. N = +5), is a strong acid, completely ionized in water. In contrast, nitrous add, HN02 (oxid. no. N = +3), is a weak acid (Ka = 6.0 X 10-4). The electronegativity effect shows up with the strengths of the oxoadds of sulfur and selenium ... 

Strategy The structure can be obtained by removing an oxygen atom from H O, (Figure 21.8). Relative acid strengths can be predicted on the basis of the electronegativity and oxidation number of the central nonmetal atom, following the rules cited above. 

Hydrogen is unusual because it can form both a cation (1I+) and ail anion (11 ). Moreover, its intermediate electronegativity (2.2 on the Pauling scale) means that it can also form covalent bonds with all the nonmetals and metalloids. Because hydrogen forms compounds with so many elements (Table 14.2 also see Section 14.2), we shall meet more of its compounds when we study the other elements. 

Now we move into the p block of the periodic table and encounter the complex bur fascinating world of the nonmetals. Here, close to the center of the periodic table, we meet strange properties, because the elements are neither so electropositive that they easily lose electrons nor so electronegative that they easily gain them. 

What Do We Need to Know Already It would be a good idea to review the information on periodic trends in Sections 1.15-1.22 and 14.1-14.2. Because the nonmetals form molecular compounds, it would also be helpful to review Lewis structures, electronegativity, and covalent bonding in Chapters 2 and 3. The bulk properties of nonmetallic materials are affected by intermolecular forces (Sections 5.1-5.5). 

B Aluminum forms an amphoteric oxide in which it has the oxidation state +3 therefore, aluminum is the element. 14.3B Hydrogen is a nonmetal and a diatomic gas at room temperature. It has an intermediate electronegativity (x — 2.2), so it forms covalent bonds with nonmetals and forms anions in combination with metals. In contrast, Group 1 elements are solid metals that have low electronegativities and form cations in combination with nonmetals. 

The first compounds to be discussed will be compounds of two nonmetals. These binary compounds are named with the element to the left or below in the periodic table named first. The other element is then named, with its ending changed to -ide and a prefix added to denote the number of atoms of that element present. If one of the elements is to the left and the other below, the one to the left is named first unless that element is oxygen or fluorine, in which case it is named last. The same order of elements is used in writing formulas for these compounds. (The element with the lower electronegativity is usually named first refer to Table 5-1.) The prefixes are presented in Table 6-2. The first six prefixes are the most important to memorize. 

The "nitrides" of most nonmetals exist. By calling the compounds nitrides, it is indicated that the other element has an electronegativity that is lower than that of nitrogen. Therefore, N02, NF3, N2F2, and the like would not be considered "nitrides" because the other element is the more electronegative. This leaves quite a number of compounds such as HN3, S4N4, (CN)2, that are covalent nitrides. Chemically, these compounds are quite different, and as will be shown later, methods for synthesizing them vary enormously. 

The group of the chalcogens sulfur, selenium and tellurium is a typical triad of the more electronegative nonmetals with relatively high-ionization energies, relatively strong element-element bonds and a clear tendency to form mono-and polyatomic anions (Table 1). 

In this chapter, we demonstrated that the restriction of building a compound with only one type of an element is not a restriction at all and a multitude of neutral, cationic as well as anionic polychalcogen structures is currently known. As expected for the more electronegative nonmetal (S) and meta metals (Se, Te), the bonding within these moieties is covalent and a small number of interactions, namely, p2-rap2 lone pair repulsion, n- and n -n bonding as well as p2- cr interactions, are sufficient to rationalize the structures and account for the bond lengths alternations or weak transannular interactions that are often found. 

The following elements have an electronegativity of 3.0 or greater N, O, F, S and Cl. These nonmetals are located in the upper right hand corner of the periodic table, but do not include H or He. 

A chemical bond exhibiting 100% covalent character and 0% ionic character occurs between identical nonmetals atoms in which the difference in electronegativity (AEN) is zero. An example is the H-H bond. There are atoms with essentially the same electronegativity, e.g. N and Cl both have an electronegativity equal to 3.0 to 2 significant figures, so the N-Cl bond would exhibit close to 100% covalent character and 0% ionic character . 

Metals are located at the left side of the periodic table and therefore, in comparison with nonmetals, have (a) fewer outer shell electrons, (b) lower electronegativities, (c) more negative standard reduction potentials and (d) less endothermic ionization energies. 

Generally, expect an ionic bond whenever you have a metal (Cs) bonded to a nonmetal (I). If you have a table of electronegativities to refer to, the electronegativity difference is greater than 1.7 for ionic compounds. 

Let s consider the bond formation between sodium and chlorine, a metal and a nonmetal. The electronegativity values of sodium and chlorine are 0.9 and 3.0 respectively. This tells us that sodium has a low ionization energy and a tendency to give electrons while chlorine has a tendency to take electrons. 

We know that the electronegativity difference between atoms must be greater than 1.9 to form an ionic bond. But if the electronegativity values of the atoms are similar, the tendency of the atoms to take or give electrons will also be similar. The transfer of electrons is not possible between such atoms, so the atoms must share electrons to gain a stable octet. The bond that is formed as a result of electron sharing is called a covalent bond. Covalent bonds are generally formed between two nonmetals. 

Ionic bonding involves the transfer of electrons from one atom to another. The more electronegative element gains electrons. The less electronegative element loses electrons. This results in the formation of cations and anions. Usually, an ionic bond forms between a metal and a nonmetal. The metal loses electrons to form a cation. The nonmetal gains electrons to become an anion. The attraction of the opposite charges forms an ionic solid. 

Which type of bond will form between two nonmetals that differ slightly in electronegativity ... 

Nonmetals follow the general trends of atomic radii, ionization energy, and electron affinity. Radii increase to the left in any row and down any column on the periodic table. Ionization energies and electron affinities increase up any column and towards the right in any row on the periodic table. The noble gases do not have electron affinity values. Ionization energies are not very important for the nonmetals because they normally form anions. Variations appear whenever the nonmetal has a half-filled or filled subshell of electrons. The electronegativity... 

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