Chemical formulas of compounds

To this point, our study of chemistry has been largely qualitative, involving very few calculations. However, chemistry is a quantitative science. Atoms of elements differ from one another not only in composition (number of protons, electrons, neutrons), but also in mass. Chemical formulas of compounds tell us not only the atom ratios in which elements are present but also the mass ratios. 

Identify the materials used and give information on the degree of and criteria for purity, but do not reference standard laboratory reagents. Give the chemical names of all compounds and the chemical formulas of compounds that are new or uncommon. Use meaningful nomenclature that is, use standard systematic nomenclature where specificity and complexity require, or use trivial nomenclature where it will adequately and unambiguously define a well-established compound. 

Molecular - OD-descriptors with high degeneracy, derived from the chemical formula of compounds and defined as - information indices of the elemental composition of the molecule, can be considered -> molecular complexity indices that take account of molecular diversity in terms of different atom types. 

Compounds can be divided into two classes molecular compounds and ionic compounds. They are described in the following table, along with examples of each. The chemical formulas of compounds show the elements that compose them. Formulas are discussed in the next section. 

The names and chemical formulas of compounds are essential vocabulary in chemistry. The system used in naming substances is called chemical nomenclature, from the Latin words nomen (name) and calare (to call). 

CHEMICAL FORMULAS OF COMPOUNDS What a Chemical Formula States... 

In cement chemistry, it is common to write the chemical formula of compounds involved in the calcination and hydration reactions by capital letters corresponding to the abbreviation of oxides. These standard symbols are Hsted in Table 15.2. For instance, the dicalcium silicate or behte can be written C S. Therefore, it is possible to represent cement composition in a ternary phase diagramm C-S-A (i.e., CaO-SiO -Al Oj). But most commercial cement compositions are restricted to the subsystem C-CjA -C S. 

Chemical formula of compounds are presented in footnote of Table 5. SA, S. aureus EC, E. coli PA, P. aeruginosa AN, A. Niger SC, S. cerevisiae Methyl Paraben, Methylp-hydroxybenzoate. Source Ref. 63. 

To write the formula for ammonium carbonate, (NH4)2C03, parentheses are used to show that two ions of ammonium are needed to balance one carbonate ion. Note two NH4 ions balance one C03 ion.) Parentheses are used when writing the chemical formula of compounds of polyatomic ions. Parentheses are not needed unless a subscript is used. For the compound lead sulfate, PbS04, only one ion of lead is used, so no parentheses are needed. 

The chemical formulas of compounds cited in this book are listed in Appendix A. Appendices B and C are glossaries of physical and chemical terms and scientific names of fish, respectively. Appendix D consists of equations for the evaluation of physico-chemical fate processes, referred to in Chapter 2. 

Chemical Formulae of Compounds Cited in this Book... 

The phase diagram for the copper-antimony system is shown on the next page. The phase diagram contains the intermetallic compound marked "X" on the diagram. Determine the chemical formula of this compound. The atomic weights of copper and antimony are 63.54 and 121.75 respectively. 

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 chemical formula of a compound represents its composition in terms of chemical symbols. Subscripts show the numbers of atoms of each element present in the smallest unit that is representative of the compound. For molecular compounds, it is common to give the molecular formula, a chemical formula that shows how many atoms of each type of element are present in a single molecule of the compound. For instance, the molecular formula for water is H20 each molecule contains one O atom and two H atoms. The molecular formula for estrone, a female sex hormone, is Clgl-I2202, showing that a single molecule of estrone consists of 18 C atoms, 22 FI atoms, and 2 O atoms. A molecule of a male sex hormone, testosterone, differs by only a few atoms its molecular formula is (lyH2802. Think of the consequences of that tiny difference ... 

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

C.3 The compound xanthophyll is a yellow compound found in bird feathers and flowers. Xanthophyll contains atoms of carbon, hydrogen, and oxygen in the ratio 20 28 1. Its molecules each have six oxygen atoms. Write the chemical formula of xanthophyll. 

If the chemical formula of a compound is already known, its mass percentage composition can be obtained from the formula. 

P, with the remainder oxygen. The mass spectrum of compound B yields a molar mass of 97.99 g-mol. Write the molecular formula of compound B. (c) Compound B reacts with an aqueous solution of calcium hydroxide to form compound C, a white precipitate. Write balanced chemical equations for the reactions in parts (a), (b), and (c). 

On the basis of the expected charges on the monatomic ions, give the chemical formula of each of the following compounds (a) magnesium arsenide (b) indium(III) sulfide ... 

Write the chemical formula of the compound represented by each of the following line structures ... 

The chemical formula for water shows how formulas are constructed. The formula lists the symbols of all elements found in the compound, in this case H (hydrogen) and O (oxygen). A subscript number after an element s symbol denotes how many atoms of that element are present in the molecule. The subscript 2 in the formula for water indicates that each molecule contains two hydrogen atoms. No subscript is used when only one atom is present, as is the case for the oxygen atom in a water molecule. Atoms are indivisible, so molecules always contain whole numbers of atoms. Consequently, the subscripts in chemical formulas of molecular substances are always integers. We explore chemical formulas in greater detail in Chapter 3. 

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 ... 

These are the correct structural formulas. Now it is a simple matter to count the number of atoms of each element and write the chemical formulas of the compounds C2 H4 CI2, C4 Hg Og, and C3 H4 O. ... 

There are many different polyatomic anions, including several that are abundant in nature. Each is a stable chemical species that maintains its stmcture in the solid state and in aqueous solution. Polyatomic anions are treated as distinct units when writing chemical formulas, naming compounds, or drawing molecular pictures. The names, formulas, and charges of the more common polyatomic anions are listed in Table 3-4. You should memorize the common polyatomic ions because they appear regularly throughout this textbook. 

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

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. 

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