Chemical formulas described

A chemical formula describes the composition of a substance by giving the relative numbers of atoms of each element. When a substance contains discrete molecules, a chemical formula is also a molecular formula. A chemical formula contains elemental symbols to represent atoms and subscripted numbers to indicate the number of atoms of each type. The simplest chemical formulas describe pure elements. The chemical formulas of most elements are their elemental symbols helium is He, silicon is Si, copper is Cu. However, seven elements occur naturally as diatomic molecules (Figure 3-lT so their chemical formulas take the form X2 A few other elements occur as atomic clusters, notably P4 and Sg. ... 

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. 

Chemical formula Describes atoms or molecules using the letter symbols of each element. H20 The chemical formula for water... 

Chemical formulas describe the simplest atom ratio (empirical formula), actual atom number (molecular formula), and atom arrangement (structural formula) of one unit of a compound. An ionic compound is named with cation first and anion second. For metals that can form more than one ion, the charge is shown with a Roman numeral. Oxoanions have suffixes, and sometimes prefixes, attached to the element root name to indicate the number of oxygen atoms. Names of hydrates give the number of associated water molecules with a numerical prefix. Acid names are based on anion names. Covalent compounds have the first word of the name for the element that is leftmost or lower down in the periodic table, and prefixes show the number of each atom. The molecular (or formula) mass of a compound is the sum of the atomic masses in the formula. Molecules are depicted by various types of formulas and models. 

Atomic sulfur formed in this reaction obviously continues reacting with vibrationally excited CO2 molecules (6-136), which leads to the additional production of CO, SO, and SO2. The total chemical formula describing non-equilibrium mechanism (6-134)-(6-137) can be summarized as... 

This is a very broad group containing monomeric and polymeric compoimds which may be classified as plasticizers or, in some cases, as slow evaporating solvents. The following chemical formulas describe stmctures of these materials ... 

The following chemical formulas describe general stmcture of polyester plasticizers Acid terminated-polyester... 

A chemical formula describes a compound in terms of its constituent elements. We will actually encounter two distinct types of chemical formulas molecular formulas and empirical formulas. The molecular formula of a compound is a kind of parts list, that describes the atomic composition of a molecule efficiently. 

Wheel symbols and markings. All responsible grinding-wheel manufacturers use a marking system established by the American Standards Association. This marking system describes the makeup of an abrasive wheel in a manner somewhat similar to the way a chemical formula describes the nature of a chemical compound. It indicates by a standard system of letters and numbers the important elements used in the manufacture of the wheel and, to a degree, the amounts and manner of their combination. 

Two-Dimensional Representation of Chemical Structures. The lUPAC standardization of organic nomenclature allows automatic translation of a chemical s name into its chemical stmcture, or, conversely, the naming of a compound based on its stmcture. The chemical formula for a compound can be translated into its stmcture once a set of semantic rules for representation are estabUshed (26). The semantic rules and their appHcation have been described (27,28). The inverse problem, generating correct names from chemical stmctures, has been addressed (28) and explored for the specific case of naming condensed benzenoid hydrocarbons (29,30). 

It is an unfortunate fact that many students and indeed design engineers are reluctant to get involved with plastics because they have an image of complicated materials with structures described by complex chemical formulae. In fact it is not necessary to have a detailed knowledge of the structure of plastics in order to make good use of them. Perfectly acceptable designs are achieved provided one is familiar with their perfonnance characteristics in relation to the proposed service conditions. An awareness of the structure of plastics can assist in understanding why they exhibit a time-dependent response to an applied force, why acrylic is transparent and stiff whereas polyethylene is opaque and flexible, etc., but it is not necessary for one to be an expert... 

Because several cyclizations have already been described in previous chapters, these are usually not repeated in this chapter but only referred to by the number of their chemical formulas, schemes, or sections. 

A molecule is a three-dimensional array of atoms. In fact, many of a molecule s properties, such as its odor and chemical reactivity, depend on its three-dimensional shape. Although molecular and structural formulas describe the composition of a molecule, they do not represent the molecule s shape. To provide information about shapes, chemists frequently use ball-and-stick models or space-filling models. 

The fact that the ratios of the three elements all came out very close to integers gives us confidence that our analysis is correct. As we describe in Chapter 4, organic acids contain the -CO2 H group. Thus, a chemical formula containing two O atoms is consistent with an organic acid. 

We can use the ideal gas equation to calculate the molar mass. Then we can use the molar mass to identify the correct molecular formula among a group of possible candidates, knowing that the products must contain the same elements as the reactants. The problem involves a chemical reaction, so we must make a connection between the gas measurements and the chemistry that takes place. Because the reactants and one product are known, we can write a partial equation that describes the chemical reaction CaC2(. ) +H2 0(/) Gas -I- OH" ((2 q) In any chemical reaction, atoms must be conserved, so the gas molecules can contain only H, O, C, and/or Ca atoms. To determine the chemical formula of the gas, we must find the combination of these elements that gives the observed molar mass. 

The lattice energy is the sum of all Ion interactions, each of which is described by Equation. Looking at this equation, we can predict that lattice energy will increase as ionic charge increases and that it will decrease as ionic size Increases. A third trend occurs in the summing of all the ion contributions Lattice energy increases with the number of ions in the chemical formula of the salt. 

C09-0083. Fluorine forms compounds whose chemical formula is XF4 with elements from groups 14, 16, and 18. Determine the Lewis structure, describe the shape, and draw a ball-and-stick model of Gep4, SeF4, and Xep4. 

C09-0105. Describe the bonding and determine the empirical chemical formula of the silicon-oxygen network of zircon. 

Determine the chemical formulas and Lewis structures of these two substances. Describe then-bonding completely, including the geometry and hybridization for each carbon atom. 

Learning to recognize the properties of a substance by examining a chemical formula is an important part of mastering chemistry. Fortunately, common acids and bases fall into a small number of structural categories. In this section we describe how to recognize acids and bases, hi Section 17-1 we explain how chemical structure influences acidity. 

The stoichiometiy of a metal complex is described by its chemical formula. For example, each cation of the silver-ammonia complex contains one Ag cation bound to two neutral NH3 ligands and carries a net charge of -i-l, as shown in Figure 18-11. The formula of a complex ion is enclosed in square brackets, as in [ Ag (NH3)2. The... 

The key to balancing complicated redox equations is to balance electrons as well as atoms. Because electrons do not appear in chemical formulas or balanced net reactions, however, the number of electrons transferred in a redox reaction often is not obvious. To balance complicated redox reactions, therefore, we need a procedure that shows the electrons involved in the oxidation and the reduction. One such procedure separates redox reactions into two parts, an oxidation and a reduction. Each part is a half-reaction that describes half of the overall redox process. 

The very basis of the kinetic model is the reaction network, i.e. the stoichiometry of the system. Identification of the reaction network for complex systems may require extensive laboratory investigation. Although complex stoichiometric models, describing elementary steps in detail, are the most appropriate for kinetic modelling, the development of such models is time-consuming and may prove uneconomical. Moreover, in fine chemicals manufacture, very often some components cannot be analysed or not with sufficient accuracy. In most cases, only data for key reactants, major products and some by-products are available. Some components of the reaction mixture must be lumped into pseudocomponents, sometimes with an ill-defined chemical formula. Obviously, methods are needed that allow the development of simple... 

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. 

A chemical equation describes a chemical reaction in many ways as an empirical formula describes a chemical compound. The equation describes not only which substances react, but the relative number of moles of each undergoing reaction and the relative number of moles of each product formed. Note especially that it is the mole ratios in which the substances react, not how much is present, that the equation describes. In order to show the quantitative relationships, the equation must be balanced. That is, it must have the same number of atoms of each element used up and produced (except for special equations that describe nuclear reactions). The law of conservation of mass is thus obeyed, and also the "law of conservation of atoms. Coefficients are used before the formulas for elements and compounds to tell how many formula units of that substance are involved in the reaction. A coefficient does not imply any chemical bonding between units of the substance it is placed before. The number of atoms involved in each formula unit is multiplied by the coefficient to get the total number of atoms of each element involved. Later, when equations with individual ions are written (Chap. 9), the net charge on each side of the equation, as well as the numbers of atoms of each element, must be the same to have a balanced equation. The absence of a coefficient in a balanced equation implies a coefficient of 1. 

Every once in a while you may run into an organic chemistry problem in Section II, on writing equations. An example is Write an equation that describes burning methanol in air. You would need to know the chemical formula and structural formula of methanol in order to do this problem. Writing organic reactions is covered in more detail in the chapter entitled Writing and Predicting Chemical Reactions. ... 

The Na+- and Ca2+-saturated montmorilIonite, saponite and beidel-lite were obtained from Dr. J. L. McAtee, Chemistry Department, Baylor University. These minerals had been purified and prepared by methods described by Callaway and McAtee (15). Included in this paper for purposes of comparison are relevant data from previous studies in which hectorite and vermiculite had been doped with paramagnetic probes ( 7, 10). The chemical formulae of the low-Fe smectites and mermiculite are reported in Table I. 

In the silicate crystal chemistry, compounds such as Mg3Al2Si30i2 are classified within the orthosilicates owing to the isolated Si044+ tetrahedra existing in their structure, and better described by a chemical formula such as Mg3Al2(Si04)3. 

The chemical formula of nitroglycerin is C3O9N3H5. Write the balanced chemical equation for the decomposition of nitroglycerin, as described in this feature. 

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