Compounds Are Represented by Chemical Formulas

The molecular formula shows the number of atoms of each element in a molecule but does not indicate how the atoms are connected to each other in space. A structural formula shows how atoms in a molecule are bonded to one another. For example, each of the two H atoms is bonded to an O atom in the water molecule, so the structural formula of water is H—O—H. The lines connecting H and O (or any atomic symbols) represent chemical bonds. Some examples of molecular and 

Sodium metal reacting with chlorine gas to form sodium chloride. 

Ionic compounds are compounds that are formed from cations and anions. Such compounds are held together by the electrostatic attraction between opposite charges. An example of an ionic compound is sodium chloride (NaCl), common table salt. The formulas of ionic compounds are usually the same as their empirical formulas because ionic compounds do not consist of discrete molecular units. For example, a solid sampk dium cl iid j((NagJ ccn s numbers of Na and Q ions 

V Potassiiim bromide. The potassium cation and the bromine anion Br  

The number of known compounds is currently weU over 20 million. Fortunately, it is unnecessary to memorize their names. Over the years, chemists have devised a system for naming chemical substances. The rules are accepted worldwide, facilitating communication among chemists and providing a useful way of labeling an overwhelming variety of substances. Mastering these rules now will prove beneficial almost immediately as we proceed with our study of chemistry. 

---

The common feature of all compounds is that they are composed of two or more elements. The full range of compounds can be divided into a few broad categories by applying ideas from the periodic table of the elements. Compounds are represented by chemical formulas, which in turn are derived from the symbols of their constituent elements. In this chapter, you will learn how to deduce and write chemical formulas and how to use the information... 

A molecular compound is made up of discrete units called molecules, which typically consist of a small number of nonmetal atoms held together by covalent bonds. Molecular compounds are represented by chemical formulas, symbolic representations that, at minimum, indicate... 

Formula unit equation A chemical equation in which all compounds are represented by complete formulas. 

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. 

We have learned how compounds are represented with chemical formulas and how they are named. We now turn to their characteristic mass. Just as an element has a characteristic mass called its atomic mass, so a compound has a characteristic mass called its foimula mass. The formula mass of a compound is computed by... 

In terms of the visual clarity of its presentation, biochemistry has still to catch up with anatomy and physiology. In this book, we sometimes use simplified ball-and-stick models instead of the classical chemical formulae. In addition, a number of compounds are represented by space-filling models. In these cases, we have tried to be as realistic as possible. The models of small molecules are based on conformations calculated by computer-based molecular modeling. In illustrating macromolecules, we used structural infor-... 

INTERSTITIAL. < 11 Descripiive of a nnnstoichiuiiiclric compound ol a metal and a nometal whose structure conforms to. 1 simple chemical formula, bill exists over a limited range of chemical composition. Imersiinal compounds are represented by borides, nitrides, and carbides ol the transition metals. 21 Descriptive n an atom of an impurity lhai causes a del cel... 

You know that many atoms covalently bond to form molecules that behave as a single unit. These units can be represented by chemical formulas and names that are used to identify them. When naming molecules, the system of rules is similar to the one you used to name ionic compounds. 

Representative examples for the preparation of selected organobismuth compounds are illustrated in the text by experimental procedures. All compounds are listed in alphabetical order, except a few which have complicated names and therefore are shown by chemical formulae at the end of this list. 

Just as an atom is the smallest part of an element, a single element is the smallest portion of a chemical compound that can be encountered. Chemical compounds are made up of two or more elements that have bonded covalently or ionically. Chemical compounds are represented by formulae, much like elements are represented by symbols. According to the Condensed Chemical Dictionary, a formula is a written representation, using symbols, of a chemical entity or relationship. There are three types of chemical formulae empirical, molecular, and structural. 

Look at the table of valencies and symbols of ions (page 464). This shows that copper(II) ions are symbolized Cu " and that sulfate ions are symbolized SO . In solution, copper(II) sulfate consists of separate copper(II) and sulfate ions. In all ionic equations, solids (whether metals or insoluble compounds) are represented by their chemical formulae. Here, we represent the zinc metal as Zn(s). The left-hand side of the chemical equation may now be written as... 

Phosphoric acid ester compound and phosphoamidate compound The phosphoric acid ester compound and phosphoamidate compound are represented by the following chemical formula (I) ... 

In this chapter, we saw that most of the substances in nature are compounds, combinations of elements in fixed ratios (4.1). Compounds are represented by their chemical formulas, which identify the type and relative amounts of each element present (4.2). For molecular compounds, a molecular formula indicates the number and type of atoms in each molecule. 

A compound is a substance that consists of two or more elements chemically combined. The elements in a compound are not simply mingled together as they are in a mixture. Instead, they are combined in a way such that the compound has properties that are different from those of the elements of which it is composed. Each compound is represented by a formula, a combination of the symbols of the elements that make up the compounds. You may already know some chemical formulas such as HjO for water, NaCl for table salt, and NH3 for ammonia. 

There seems, however, to-day, to be overwhelming evidence that the French chemists were correct and that citronellol and rhodinol are two very similar, but chemically different, compounds, citronellol being represented by the formula (1) and rhodinol by formula (2). Considerable evidence of this is to be found in the work of Barbier and Locquin. Starting from the acetic esters of ordinary d-citronellol and rhodinol from oil of geranium or rose, they attached hydrogen chloride to the double bond, and obtained the same additive product according to the equations — ... 

Another closely related family of superconductors is represented by the formula TlBa2Can 1Cun02n+3 (n = 1, 2, 3, 4, 5). They contain single layers of T1 and O atoms that separate the perovskite-like Ba-Cu-Ca-O slabs (24)(25)(26)(27) (Figure 6). Distortions in the Tl-O sheets are also found in these compounds (26)(27). Note that if these phases were stoichiometric, copper would always have a formal oxidation state of greater than two. Therefore, the chemical composition of this homologous series allows the existence of holes in the copper-oxygen sheet. 

Tins symbols employed in chemical formula to-day are, with a few alterations and additions, those used by Berzelius. The formula of simple compounds were represented by writing the symbols of the elements contained in the compound side by side, and this simple representation served for some time. The formulae used, however, did not denote the proportion of the atoms of one kind to that of another kind, and numerals were therefore introduced to denote the number of each kind of atoms in the molecule. This arose naturally when it was found that more than one compound might contain the same elements, and that the different properties of the compounds were due to the proportion of the elements present in the molecule as, for example, the two compounds of carbon and oxygen, carbon monoxide and carbon dioxide. 

A compound is represented by its chemical formula, in which the symbols for the elements are written together. The chemical formula for sodium chloride is NaCl and that for ammonia is NH3. Numerical subscripts indicate the ratio in which the atoms combine. By convention, the subscript 1 is understood and omitted. So the chemical formula NaCl tells us that in the compound sodium chloride there is one sodium for every one chlorine, and the chemical formula NH3 tells us that in the compound ammonia there is one nitrogen atom for every three hydrogen atoms, as Figure 2.12 shows. 

The compounds sodium chloride and ammonia are represented by their chemical formulas, NaCl and NH3. A chemical formula shows the ratio of atoms used to make the compound. 

Typically, reactants and products are represented by their atomic or molecular formulas, but molecular structures or simple names may be used instead. Phases are also often shown (s) for solid, ( ) for liquid, and (g) for gas. Compounds dissolved in water are designated (aq) for aqueous. Lastly, numbers are placed in front of the reactants or products to show the ratio in which they either combine or form. These numbers are called coefficients, and they represent numbers of individual atoms and molecules. For instance, to represent the chemical reaction in which coal (solid carbon) burns in the presence of oxygen to form gaseous carbon dioxide, we write the chemical equation... 

Thus, e.g. as in the typical investigation in Ref. [110], long-range intramolecular electron transfer has been detected for rigid bifunctional steroid molecules dissolved in THF. The structural formulae of these compounds are represented in Fig. 16. The donor acceptor pairs I-V presented in this figure are separated by various numbers, n, of similar chemical bonds, the so-called n-bond system. The anion-radicals of molecules I-V were obtained via reactions of these molecules... 

Asymmetrical nitrido Tc(V) complexes (simply defined as heterocomplexes) are defined as coordination compounds in which two different bidentate ligands are bound to the same Tc=N group, and are represented by the general formula [Tc(N)(L)(L )]"+/0/". The attempt to develop a high-yield synthesis of these types of complexes may first appear to be prevented by basic chemical considerations. Actually, it is reasonable to expect that the reaction of two different bidentate ligands, A and B, with the same Tc=N group would always yield a statistical mixture of symmetrical and asymmetrical complexes, namely [Tc(N)(A)2], [Tc(N)(B)2] and [Tc(N)(A)(B)]. However, the peculiar properties of mixed 7r-acceptor-7r-donor ligands offered the route to the solution of this synthetic problem. The key approach can be outlined as follows. 

---