Symbols of the Elements

We all recognize Mr., N.Y., and Ave. as abbreviations for mister. New York, and avenue, respectively. In a like manner, each element also has an abbreviation these are symbols called symbols of the elements. Fourteen elements have a single letter as their symbol, and the rest have two letters. A symbol stands for the element Itself, for one atom of the element, and (as we shall see later) for a particular quantity of the element. 

The symbols and names of all the elements are given in the table on the inside front cover of this book. Table 3.3 lists the more commonly used elements and their symbols. Examine Table 3.3 carefully and you will note that most of the symbols start with the same letter as the name of the element that is represented. A number of symbols, however, appear to have no connection with the names of the elements they represent (see Table 3.4). These symbols have been carried over from earlier names (usually in Latin) of the elements and are so firmly implanted in the literature that their use is continued today. 

Element Symbol Element Symbol Element Symbol 

TABLE 3.4 Symbols of the Elements Derived from Early Names  

Chunks of sulfur are transported in baskets from a mine in East Java. 

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The composition of a nucleus is shown by its nuclear symbol. Here, the atomic number appears as a subscript at the lower left of the symbol of the element The mass number is written as a superscript at the upper left... 

Quite often, isotopes of an element are distinguished from one another by writing the mass number after the symbol of the element The isotopes of uranium are often referred to as U-235 and U-238. 

In the periodic table, atomic masses are listed directly below the symbol of the element. In the table on the inside front cover of this text, atomic masses are cited to four significant figures. That ordinarily will be sufficient for our purposes, although more precise values are available (see the alphabetical list of elements on the inside back cover). 

Give the symbol of the element of lowest atomic number whose ground state has... 

This idea is readily extended to simple molecules of compounds formed by nonmetal atoms. An example is the HF molecule. You will recall that a fluorine atom has the electron configuration ls22s22p5. ft has seven electrons in its outermost principal energy level (n = 2). These are referred to as valence electrons, in contrast to the core electrons filling the principal level, n = 1. If the valence electrons are shown as dots around the symbol of the element, the fluorine atom can be represented as... 

The outstanding characteristic of the actinide elements is that their nuclei decay at a measurable rate into simpler fragments. Let us examine the general problem of nuclear stability. In Chapter 6 we mentioned that nuclei are made up of protons and neutrons, and that each type of nucleus can be described by two numbers its atomic number (the number of protons), and its mass number (the sum of the number of neutrons and protons). A certain type of nucleus is represented by the chemical symbol of the element, with the atomic number written at its lower left and the mass number written at its upper left. Thus the symbol... 

Appendix 2D lists the names and chemical symbols of the elements and gives the origins of their names. 

First check to see whether the compounds are ionic or molecular. Many compounds that contain a metal are ionic. Write the symbol of the metal first, followed by the symbol of the nonmetal. The charges on the ions are determined as shown in Examples C.l and C.2. Subscripts are chosen to balance charges. Compounds of two nonmetals are normally molecular. Write their formulas by listing the symbols of the elements in the same order as in the name, with subscripts corresponding to the Greek prefixes used. 

As will become apparent as this chapter progresses, many of our basic ideas on the chemical bond were proposed by Ci. N. Lewis, one of the greatest of all chemists, in the early years of the twentieth century. Lewis devised a simple way to keep track of valence electrons when atoms form ionic bonds. He represented each valence electron as a dot and arranged the dots around the symbol of the element. A single dot represents an electron alone in an orbital a pair of dots represents two paired electrons sharing an orbital. Examples of the Lewis symbols of atoms are... 

Observing and Inferring Identify which element was more active and which element was less active in each of the six tests conducted. Summarize the information in Data Table 3 by writing the symbol of the element in the appropriate space. 

The number of protons in the nucleus determines the chemical properties of the element. That number is called the atomic number of the element. Each element has a different atomic number. An element may be identified by giving its name or its atomic number. Atomic numbers may be specified by use of a subscript before the symbol of the element. For example, carbon may be designated 6C. The subscript is really unnecessary, since all carbon atoms have atomic number 6, but it is sometimes useful to include it. Atomic numbers are listed in the periodic table and in Table 3-1. 

Electron dot formulas are useful for deducing the structures of organic molecules, but it is more convenient to use simpler representations—structural or graphic formulas—in which a line is used to denote a shared pair of electrons. Because each pair of electrons shared between two atoms is equivalent to a total bond order of 1, each shared pair can be represented by a line between the symbols of the elements. Unshared electrons on the atoms are usually not shown in this kind of representation. The resulting representations of molecules are called graphic formulas or structural formulas. The structural formulas for the compounds (a) to (e) described in Example 21.1 may be written as follows ... 

Nuclear equations are written with both the total charge and the total of the mass numbers unchanged from reactants to products. That is, the total of the subscripts of the reactants equals the total of the subscripts of the products and the total of the superscripts of the reactants equals the total of the superscripts of the products. The subscripts of isotopes may be omitted because the symbol of the element gives the atomic number. 

There are several forms in which the elements of the periodic chart may be arranged. The version shown here is one of the forms now in widespread use. Groups I, II, III, etc., and the noble gases are called the Main Group Elements. All of their inner shells are fully occupied with electrons. The other elements are called the Transition Elements. They all have at least one inner shell that is only partially filled with electrons. Referring to the entire table, the numbers written above the symbols of the elements (always whole numbers) are the atomic numbers of the elements, and the numbers written below the symbols of the elements (not necessarily whole numbers) are the atomic weights of the elements. Parentheses indicate insufficient information exists or material is not yet official. 

The minimum information needed is the atomic number (or some way to obtain it the name or the symbol of the element involved), the number of electrons (or some way to obtain it, such as the charge on the species), and the mass number (or the number of neutrons). 

This representation is also known as the Lewis symbol representation. In this representation valence electrons are shown as dots around the symbol of the element. 

In some cases, it would be convenient to condense the electron configuration. In this condensed form, the electronic configuration of the previous noble gas forms a core represented by the atomic symbol of the element enclosed in brackets (i.e., [He] or [Ne]). The electrons added since the noble gas, follow the noble gas core. For example, cobalt can be represented as an argon core plus the 4s and 3d electrons. Thus, ls22s22p63s23p64s23d7 becomes [Ar]4s23d7. 

For all the structures included, the environmental data by Daams et al. (1991) are given indicating for every atom the corresponding coordination number (CNE) and the polyhedron code. The symbols of the elements at the vertices of this polyhedron are then listed in the order of increasing distances from the central atom. 

EQUATION (chemical) A representation of a chemical reaction, using the symbols of the elements to represent the actual atoms and molecules taking part in a reaction. For example, a classical, but simplified, overall reaction for the deflagration of gunpowder is as follows ... 

The changes which occur during chemical action are expressed by equations, in which the symbols of the elements or compounds, as they exist before the change, are placed on the left, and those which result from the reaction on the right. Thus, taking an example from each of the five kinds of chemical action above mentioned, we have... 

In symbolic notation, the same idea is couveyed by the use of dashes and Boman numerals placed above and to the right of the symbol of the element thus,... 

To specify the atomic and mass numbers of an element, chemists typically write the symbol of the element in the form where Z is the atomic number, A is the mass number, and X is... 

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. 

We may represent this reaction by a simple diagram. The symbols of the elements involved are placed in a horizontal line, at loci representing their electronegativity values. Above the symbols arcs are drawn to indicate the single bonds in the reactants, and below the symbols arcs are drawn to represent the single bonds in the product ... 

Free sadfeals. IUPAC recommends that the use of the word radical be restricted to species conventionally termed free radicals. A radical is indicated by a dot ns right superscript to the symbol of the element or group. The formulae of polyatomic radicals are placed in parentheses and the dot is placed as a right superscript to the parentheses. In radical ions, the dot precedes the charge. 

Nuclear symbolism disregards valence and electrons and always includes the mass number of the isotope (the whole number nearest the atomic weight of the isotope), the atomic number of the element, and the symbol of the element. The mass number is shown as a superscript preceding the symbol, and the atomic number is shown as a subscript preceding the symbol. This notation is illustrated by the following examples ... 

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