Chemical formulas ionic compounds

Naming ionic compounds Chemical nomenclature is a systematic way of naming compounds. Now that you are famihar with writing chemical formulas, you will use the following general rules in naming ionic compounds when their formulas are known. 

What is the chemical formula for this compound You have learned that the formula for an ionic compound represents the simplest possible ratio of the ions present and is called a formula unit. Chemical formulas for most ionic compounds are the same as their empirical formulas. Because the unknown compound is ionic, the chemical formula for a formula unit of the compound is the same as its empirical formula, NaC104. The compound is called sodium perchlorate. 

A formula unit of a substance is the group represented by the substance s chemical formula, that is, a group containing the kinds and numbers of atoms or ions listed in the chemical formula. Formula unit is a general term that can be used in reference to elements, molecular compounds, or ionic compounds. One formula unit of the noble gas neon, Ne, contains one neon atom. In this case, the formula unit is an atom. One formula unit of water, Ff20, contains two hydrogen atoms and one oxygen atom. In this case, the formula unit is a molecule. One formula unit of ammonium chloride,... 

Chemical Formulas Compoimds are represented by chemical formulas, which indicate the elements present in the compound and the relative number of atoms of each. These formulas represent the basic units that make up a compound. Pure substances can be categorized according to the basic units that compose them. Elements can be composed of atoms or molecules. Compounds can be molecular, in which case their basic units are molecules, or ionic, in which case their basic imits are ions. The formulas for many ionic compoimds can be written simply by knowing the elements in the compound. Chemical Formulas To understand compounds, we must understand their composition, which is represented by a chemical formula. The connection between the microscopic world and the macroscopic world hinges on the particles that compose matter. Since most matter is in the form of compounds, the properties of most matter depend on the molecules or ions that compose it. Molecular matter does what its molecules do ionic matter does what its ions do. The world we see and experience is governed by what these particles are doing. 

The chemical formula of an ionic compound shows the ratio of the ions present in a sample of any size. A formula unit is the simplest collection of atoms from which an ionic compound s formula can be written. For example, one formula unit of sodium chloride, NaCI, is one sodium cation plus one chloride anion. (In the naming of a monatomic anion, the ending of the element s name becomes -ide.)... 

A major task of chemical analysis is to determine the formulas of compounds. The formula found by the approach described here is the simplest formula, which gives the simplest whole-number ratio of the atoms present. For an ionic compound, the simplest formula is ordinarily the only one that can be written (e.g., CaCl2, Cr203). For a molecular compound, the molecular formula is a whole-number multiple of the simplest formula, where that number may be 1,2. 

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. 

C02-0069. Write the chemical formulas of all ionic compounds that can form between the elements listed in Problem 2.41. 

C02-0071. Aluminum is one of the few elements that forms cations with +3 charge. What are the chemical formulas of the ionic compounds that form between aluminum and (a) oxygen (b) fluorine ... 

Here are some specific examples illustrating chemical formulas of ionic compounds. 

Ionic compounds are named using the same guidelines used for naming binary molecules, except that the cation name aiways precedes the anion name. Thus, NH4 NO3 is ammonium nitrate, Na2 CO3 is sodium carbonate, and Ca3 (P04)2 is caicium phosphate. The subscripts are not specified in these names because the fixed ionic charges determine the cation-anion ratios unambiguously. Example 3-6 reinforces these guidelines by showing how to construct chemicai formulas from chemical names. 

By convention, the chemical formulas of many ionic compounds do not explicitly state the charges of the ions. It is not necessary to do so when the species involved form ions with only one possible charge. However, many metals form more than one type of stable cation. For example, copper forms two different oxides, black CuO and red C112 O. The oxide anion has a -2 charge, so for the first compound to be neutral the copper cation must bear a +2 charge. In C112 O, each copper ion must have +1 charge. 

Many ionic compounds can have water molecules incorporated into their solid structures. Such compounds are called hydrates. To emphasize the presence of discrete water molecules in the chemical structure, the formula of any hydrate shows the waters of hydration separated from the rest of the chemical formula by a dot. A coefficient before H2 O indicates the number of water molecules in the formula. Copper(II) sulfate pentahydrate is a good example. The formula of this beautiful deep blue solid is C11SO4 5 H2 O, indicating that five water molecules are associated with each CuSOq unit. Upon prolonged heating, CuSOq 5 H2 O loses its waters of hydration along with its color. Other examples of hydrates include aluminum nitrate nonahydrate, A1 (N03)3 9 H2 O,... 

The word bonding applies to any situation in which two or more atoms are held together in such close proximity that they form a characteristic species which has distinct properties and which can be represented by a chemical formula. In compounds consisting of ions, bonding results from the attractions between the oppositely charged ions. In such compounds in the solid state, each ion is surrounded on all sides by ions of the opposite charge. (For example, see Fig. 5-1.) In a solid ionic compound, it is incorrect to speak of a bond between specific pairs of ions. 

An antisite defect is an atom on a site normally occupied by a different chemical species that exists in the compound. Antisite defects are a feature of a number of important materials, especially weakly ionic or covalently bonded ones. In a compound of formula AB the antisite defects that can occur are an A atom on a site normally occupied by a B atom (Fig. 1.16a), or a B atom on a site normally occupied by an A atom (Fig. 1.16b). 

An ionic solid solution, on the other hand, is of variable composition. Its chemical formula can not be written in simple integer ratio numbers. A theoretical example is that of two compounds AX and BX which form a solid solution of the general formula ... 

In addition to these actinide(IV) compounds, the increasing stabihty of the - -3 oxidation state for the trans-uranium elements has recently led to the preparation of compounds of formula K[M(CgH8)2] where M=Np or Pu 31). In their chemical behavior these compounds axe similar to the corresponding lanthanide complexes vide infra) and their X-ray powder patterns suggest they have the same structure. They appear to be much more ionic than their -f4 analogues. 

Cations and anions combine in very predictable ways within ionic compounds, always acting to neutralize overall charge. Therefore, the name of an ionic compound implies more than just the identity of the atoms that make it up. It also helps you determine the correct chemical formula, which tells you the ratio in which the elements combine. Consider these two examples, both of which involve lithium ... 

It is to be expected that all molecules of type AB have dipole moments if they consist of ions, yet it is found that the molecules H2, 025 N2, Cl2, Br2 and I2 are non-polar. It is therefore clear that these molecules are not composed of ions, and that the formulae H+H, Cl+Cl-, etc. must be discarded. The chemical bond in these molecules must be of an entirely different kind from that in purely ionic compounds. It is to be remembered that it was expected that NaCl has a moment of 13-2 X 10-18, whereas the experimental value is 10 X 10"-18. In view of the great experimental difficulties in measuring the dipole moment of NaCl in the vapour state, this agreement can be considered satisfactory. 

What is the chemical formula for the ionic compound magnesium oxide ... 

Magnesium ions carry a 2+ charge, and chloride ions carry a 1— charge. What is the chemical formula for the ionic compound magnesium chloride ... 

The chemical formula of an ionic compound shows the ratio of the numbers of atoms of each element present in the compound in terms of the smallest whole numbers of ions. A formula unit of an ionic compound is a group of ions with the same number of each element as appears in its formula. 

The second group of compounds is formed by the compounds with exclusively ionic bonds. These compounds include metals (left in the formula and with the lowest EN-value) and the chemical formulas are simple, for example ... 

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