Electrically neutral formula

The ions Na, Mg, and CP are monatomic, meaning that each consists of a single ionized atom. By contrast, a polyatomic ion is made up of fwo or more atoms. In the nitrate ion, NOs , the subscripts signify fhaf three O atoms and one N atom are joined by covalent bonds into the single ion NOs . Magnesium nitrate is an ionic compound made up of magnesium and nitrate ions. An electrically neutral formula unit of this compound must consist of one Mg " ion and two NOs ions. The formula based on this formula unit is denoted by enclosing NO3 in parentheses, followed by the subscript 2 thus, Mg(N03)2- Polyatomic ions are discussed further in Section 3-6. 

In each case, identify the cations and their charges, based on periodic table group numbers or on oxidation states appearing as Roman numerals in names Ba, Ca, and Fe. Then identify the anions and their charges 0 , F, and Combine the cations and anions in the relative numbers required to produce electrically neutral formula units. 

To predict the formula of an ionic compound, you need to know the charges of the two ions involved. Then you can apply the principle of electrical neutrality, which requires that the total positive charge of the cations in the formula must equal the total negative charge of the anions. Consider, for example, the ionic compound calcium chloride. The ions present are Ca2+ and Cl-. For the compound to be electrically neutral, there must be two Cl- ions for every Ca2+ ion. The formula of calcium chloride must be CaCl indicating that the simplest ratio of Cl- to Ca2+ ions is 2 1. 

You know die charge of die complex and those of the ligands. To find the formulas of the coordination compounds, apply the principle of electrical neutrality. 

The formulas of ionic compounds have a different meaning from those of molecular compounds. Each crystal of sodium chloride has a different total number of cations and anions. We cannot simply specify the numbers of ions present as the formula of this ionic compound, because each crystal would have a different formula and the subscripts would be enormous numbers. However, the ratio of the number of cations to the number of anions is the same in all the crystals, and the chemical formula shows this ratio. In sodium chloride, there is one Na+ ion for each Cl ion so its formula is NaCl. Sodium chloride is an example of a binary ionic compound, a compound formed from the ions of two elements. Another binary compound, CaCl2, is formed from Ca2+ and Cl- ions in the ratio 1 2, which is required for electrical neutrality. 

Work from name to formula, using information about polyatomic ions and being careful to build a formula that is electrically neutral. 

Just as each element has a characteristic molar mass, so does every chemical compound. Chemical compounds are composed of atoms bound together into molecules or ions clustered together in electrically neutral aggregates. In either case a chemical formula describes the atomic composition of a compound. 

Begin by finding the chemical formula from the name, nickel(II) chloride hexahydrate. Chloride ion carries -1 charge, and the (II) indicates that nickel is a +2 cation. Electrical neutrality requires two chlorides for every nickel. The name also tells us that the salt contains six water molecules for each unit of nickel(II) chloride. Thus, each formula unit of the salt contains one cation, two Cl anions,... 

Thus, in weak electrolytes, molecules can exist in a similar way as in non-electrolytes—a molecule is considered to be an electrically neutral species consisting of atoms bonded together so strongly that this species can be studied as an independent entity. In contrast to the molecules of non-electrolytes, the molecules of weak electrolytes contain at least one bond with a partly ionic character. Strong electrolytes do not form molecules in this sense. Here the bond between the cation and the anion is primarily ionic in character and the corresponding chemical formula represents only a formal molecule nonetheless, this formula correctly describes the composition of the ionic crystal of the given strong electrolyte. 

Each additional samaria formula unit creates one oxygen vacancy. The concentration of the vacancies is given by the electrical neutrality condition, 2[Sm Ce] = [V0 inferring that the vacancy concentration is linearly dependent on the dopant level. The ionic conductivity, a, can be calculated by... 

The formula as deduced from chemical and X-ray structural analysis is Na lgSi C S There is an open framework of Si04 tetrahedra with shared corners. Some silicon ions are replaced by aluminium ions, however, and to preserve electrical neutrality sodium cations are needed. These are in excess and the overall balance is maintained by the S2, S22 and S32- ions present. Consequently, chemical formulae containing fractional proportions of elements are possible. 

Metal cations team up with nonmetal anions to form ionic compounds. What s more, the ratio of cations to anions within each formula unit depends on the charge assumed by the fickle transition metal. The formula unit as a whole must be electrically neutral. The rules you follow to name an ionic compound must accommodate the whims of transition metals. The system of Roman numerals or suffixes applies in such situations ... 

Compounds containing polyatomic ions follow similar rules. In sodium carbonate, there are two Na+ ions per carbonate ion, so its formula is Na2C03. When a subscript has to be added to a polyatomic ion, the ion is written within parentheses, as in (NH4)2S04, where (NH4)2 means that there are two NH4+ (ammonium) ions for each S042- (sulfate) ion in ammonium sulfate. In each case, the ions combine in such a way that the positive and negative charges cancel all compounds are electrically neutral overall. 

Now we can work out the formula of an ionic compound formed between the monatomic ions of two main-group elements, one a metal and the other a nonmetal. Unless a lower oxidation number is specified (as for the p-block metals), the metal atom loses all its valence electrons, and the nonmetal atom gains enough electrons to complete its valence shell. Then we adjust the numbers of cations and anions so that the resulting compound is electrically neutral. A simple example is calcium chloride. The calcium atoms ([Ar]4s2) each lose two electrons, to form... 

Ca2+ ions ([Ar]). One electron can be accommodated in the single vacancy of a Cl atom ([Ne]3s23p5) to form a Cl ion ([Ne]3s23p6). To achieve an electrically neutral substance, two Cl- ions are needed for each Ca2+ ion so the chemical formula of calcium chloride is CaCl2. 

Each tetrahedron represents an Si04 structural unit, with an Si atom at the center of the tetrahedron and an O atom at each corner. Each terminal (unshared) O atom needs one electron to complete its octet and therefore has a charge of —1. Each bridging (shared) O atom completes its octet by forming bonds to two Si atoms and is therefore electrically neutral. To find the number of Si atoms in the formula, count the number of tetrahedra. To find the number of O atoms, count the number of corners (shared and unshared). To find the charge on the anion, count the number of unshared corners. 

Not all coordination compounds are neutral molecules like Pt(NH3)2Cl2. Many are salts, such as [Ni(NH3)6]Cl2 and K3[Fe(CN)6], which contain a complex cation or anion along with enough ions of opposite charge to give a compound that is electrically neutral overall. To emphasize that the complex ion is a discrete structural unit, it is always enclosed in brackets in the formula of the salt. Thus, [Ni(NH3)6]Cl2 contains [Ni(NH3)6]2+ cations and Cl- anions. The term metal complex (or simply complex) refers both to neutral molecules, such as Pt(NH3)2Cl2, and to complex ions, such as [Ni(NH3)6]2+ and [Fe(CN)6]3-. 

To find the formula and charge of the complex cation or anion, note the number of ligands of each type, their charge, and the oxidation state of the metal in the name of the compound or ion. If the name refers to an electrically neutral compound, balance the charge of the complex cation or anion with the appropriate number of ions of opposite charge. 

Formulas of Ionic Compounds As we mentioned earlier, compounds (like atoms) must be electrically neutral. The net charge on an ionic compound must be zero. When a metal gives its electrons away to form a cation, there has to be some other species, often a nonmetal, present to accept the electrons. Thus, whenever a cation is forming, there is also a concurrent formation of an anion. Chemical systems have to remain electrically neutral. 

As you recall, molecules are comprised of atoms chemically bonded into a discrete and identifiable unit. There are no ionic molecules, because every cation is attracted to every anion, so there are no identifiable ion pairs that belong exclusively to each other. Therefore, the formula of an ionic compound is an empirical formula. That is, the formula of an ionic compound lists the simplest ratio of cations to anions necessary to achieve electrical neutrality. For example, calcium oxide contains Ca2+ ions and O2- ions. While the formulas CaO and Ca202 both represent electrically neutral combination of ions, the subscripts in the latter formula have a common factor of 2. Therefore, Ca202 is not the simplest ratio of calcium cations to oxide anions. Therefore, the formulation of calcium oxide as Ca202 is incorrect. The correct empirical formula of calcium oxide is CaO. 

The structure of crystalline FeO belongs to the NaCl type. When iron(II) oxide is prepared under normal conditions, the composition of the product (wustite) is always Fei 50. In order to retain overall electric neutrality, part of the Fe2+ is oxidized to Fe3+, and the chemical formula becomes Fc Fe. O. Since the radius of Fe3+ is small, the Fe3+ cations tend to occupy the tetrahedral holes to form a short-range ordered Fe40io cluster, which is called the Koch cluster of Fei 0, as shown in Fig. 10.1.3. The Koch clusters are distributed randomly in the crystal structure. To satisfy charge neutrality, the formation of a Koch cluster must be accompanied by the presence of six Fe2+ vacancies, one of which is located at the center of the cluster, and the remaining five are distributed randomly at the centers of the edges of the cubic unit cell. 

The structure of WO3 is of the Re03 type, as shown in Fig. 10.4.4(a). The tungsten bronzes of the formula MxW03 (0 < x < 1) are derived from the three-dimensional network of WO3, in which the W atoms adopt variable valence states, and the large unoccupied interstices conveniently accommodate other cationic species. When a portion of the WfH cations is converted to W5+, the requisite cations M (normally Na or K but also Ca, Sr, Ba, Al, In, Tl, Sn, Pb, Cu, Ag, Cd, lanthanides, H+, and NHj) are incorporated into the structure to maintain electrical neutrality. The additional cations M are partially located at the centers of the unit cells to give the perovskite stmcture type, as shown in Fig. 10.4.4(b). 

The cohesion in crystals of electrically neutral atoms, typified in Figure 5.10 by Ar, is ascribed to van der Waals interaction, generated by zero-point fluctuation of the electron density and its polarization effect on neighbouring atoms. The energy of interaction is given by the London formula, as a function of zero-point vibration frequency, between atoms at a distance d apart, as ... 

If one counts the positive and negative chafes of these formulas it is noted that CH4 and CC14 are electrically neutral, but that the sulphate ion has a net of 2 negative charges, S04, and the perchlorate ion has a net of one negative charge, C104 . 

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