Anion monatomic anions

Monatomic anions are named by adding the suffix -ide to the stem of the name of the nonmetal from which they are derived. 

FIGURE C.7 The typical monatomic anions formed by a selection of elements in the periodic table. Notice how the charge on each ion depends on its group number. Only the nonmetals form monatomic anions under common conditions. 

Monatomic anions, such as the Cl- ions in sodium chloride and the O2- ions in quicklime (CaO), are named by adding the suffix -ide and the word ion to the first part of the name of the element (the stem" of its name), as shown in Table D.l thus, S2 is a sulfide ion and O2 is an oxide ion. There is usually no need to specify the charge, because most elements that form monatomic anions form only one kind of ion. The ions formed by the halogens are collectively called halide ions and include fluoride (F ), chloride (Cl-), bromide (Br-), and iodide (I ) ions. 

Names of monatomic anions end in -ide. Oxoanions are anions that contain oxygen. The suffix -ate indicates a greater number of oxygen atoms titan the suffixe -ite within the same series of oxoanions. 

To predict the electron configuration of a monatomic cation, remove outermost electrons in the order np, ns, and (n — l)d fora monatomic anion, add electrons until the next noble-gas configuration has been reached. The transfer of electrons results in the formation of an octet (or duplet) of electrons in the valence shell on each of the atoms metals achieve an octet (or duplet) by electron loss and nonmetals achieve it by electron gain. 

All ionic bonds have some covalent character. To see how covalent character can arise, consider a monatomic anion (such as Cl-) next to a cation (such as Na+). As the cation s positive charge pulls on the anion s electrons, the spherical electron... 

Monatomic cations with constant charges Monatomic cations with variable charges Polyatomic cations Monatomic anions Oxyanions... 

Common anions may be grouped as follows monatomic anions, oxyanions, and special anions. There are special endings for the first two groups the third group is small enough to be memorized. 

The charge on every monatomic anion is equal to the group number minus 8 (or 18, if the most modern periodic table group numbering system is used). 

What is the difference in the rules for remembering charges on monatomic anions and oyxanions ... 

C—All the other elements are nonmetals. Nonmetals usually form monatomic anions. 

The hydration of anions is regarded as being electrostatic with additional hydrogen bonding. The number of water molecules in the primary hydration sphere of an anion depends upon the size, charge and nature of the species. Monatomic anions such as the halide ions are expected to have primary hydration spheres similar to those of monatomic cations. Many aqueous anions consist of a central ion in a... 

The enthalpies of formation of aqueous ions may be estimated in the manner described, but they are all dependent on the assumption of the reference zero that the enthalpy of formation of the hydrated proton is zero. In order to study the effects of the interactions between water and ions, it is helpful to estimate values for the enthalpies of hydration of individual ions, and to compare the results with ionic radii and ionic charges. The standard molar enthalpy of hydration of an ion is defined as the enthalpy change occurring when one mole of the gaseous ion at 100 kPa (1 bar) pressure is hydrated and forms a standard 1 mol dm-3 aqueous solution, i.e. the enthalpy changes for the reactions Mr + (g) — M + (aq) for cations, X (g) — Xr-(aq) for monatomic anions, and XOj (g) —< XO (aq) for oxoanions. M represents an atom of an electropositive element, e.g. Cs or Ca, and X represents an atom of an electronegative element, e.g. Cl or S. 

A general equation for the calculation of the standard entropy of a monatomic anion is ... 

To form monatomic anions, we add enough electrons to complete the valence shell. For example, nitrogen has five valence electrons (4), so three more electrons are needed to reach a noble-gas configuration, that of neon. Therefore, the ion will be N3" (5). 

If the atom has more electrons in the molecule than when it is a free, neutral atom, then the atom has a negative formal charge, like a monatomic anion. If the assignment of electrons leaves the atom with fewer electrons than when it is free, then the atom has a positive formal charge, as if it were a monatomic cation. Mathematically, we write... 

All ionic bonds have some covalent character. To see how covalent character can arise, consider a monatomic anion (such as Cl ) next to a cation (such as Na ). As the cation s positive charge pulls on the anion s electrons, the spherical electron cloud of the anion becomes distorted in the direction of the cation. We can think of this distortion as the tendency of an electron pair to move into the region between the two nuclei and to form a covalent bond (Fig. 2.11). Ionic bonds acquire more covalent character as the distortion of the electron cloud on the anion increases. 

One special difficulty of applying parameterized models to chemical reactions deserves a special mention, namely that transition states often have charge distributions quite different from those against which solvation models are parameterized. For example, the partial atomic charge on Cl in the (Cl... CH3... Cl)-1 SN2 transition state is about -0.7, midway between the values (-1.0 and about -0.4, respectively) found in Cl-monatomic anion and typical alky chlorides. Thus the atomic radii and atomic surface tensions optimized against equilibrium free energies needs to be re-validated for transition structures. 

The anion (negative ion) is named and written last. Monatomic anions are formed from nonmetallic elements and are named by replacing the end of the element s name with the suffix -ide. 

Binary acids, acids that are formed from a hydrogen ion bonding to a monatomic anion, are named by placing the term hydro- in front of the root of the anion ending in -ic. For instance, HC1 is called hydrochloric acid. 

Ternary ionic compounds are ionic compounds containing one or more polyatomic ions. The possible combinations are a monatomic cation bonded to a polyatomic anion, a polyatomic cation bonded to a monatomic anion, or a polyatomic cation bonded to a polyatomic anion. There are additional rules that must be added to the rules in the previous section ... 

The detailed electronic structures of monatomic ions may be deduced starting from the structures of the corresponding neutral atoms (presented in Chapter 4). Monatomic anions have simply added sufficient electrons to the outermost p subshell to complete that subshell. The + rule can be used to deduce the structure of the ion as well as that of the neutral atom. For example, the electronic configuration of the nitride ion (the anion of nitrogen) is deduced, starting with the configuration of nitrogen ... 

The charge on every monatomic anion (except H ) is equal to the classical group number of the element minus 8. The number of added electrons is the absolute value of that difference. 

Most main group cations and all monatomic anions have characteristic charges that are easy to learn, so in their compounds with other ions, the charges on the other ions are easy to deduce. 

Nonmetal atoms accept electrons from metal atoms if the metal atoms are available, or else they share electrons they never donate electrons to form monatomic cations. The largest charge on any monatomic cation is 4 -I-, and on any monatomic anion, it is 3 —. 

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