Chemists notation

The conventional cement chemists notation uses abbreviations for the most common constituents calcium oxide [1305-78-8], CaO, = C siUcon dioxide... 

Calculated by the American Society for Testing and Materials C150-76 (24). In cement chemists notation. 

In cement chemists notation, where subscripts x andj indicate variable unknown quantities. 

In hydrations at ordinary temperatures (27) pure C S and P-C2S, corresponding to the aHte and beHte phases ia Pordand cements, respectively, react with water to form calcium hydroxide and a single calcium siHcate hydrate (C—S—H). Using cement chemists notation... 

Conversely, lower pressures favor formation of styrene. So the logic is that steam mixed with the EB permits cracking the hydrogen off at lower pressure and favors the styrene staying cracked. (You may have noticed the chemical equation in Figure 8—6 has arrows going both directions. Thats the chemists notation for this reversibility.)... 

Fig. A.I. Real spherical harmonics. The first one, Y , is a constant. The coordinate system attached to the unit sphere is shown. The two zonal harmonics, IT and II, section the unit sphere into vertical zones. The unshaded area indicates a positive value for the harmonics, and the shaded area indicates a negative value. The four sectoral harmonics are sectioned horizontally. The two tesserai harmonics have both vertical and horizontal nodal lines on the unit sphere. The corresponding "chemists notations," such as (3z — r ), are also marked.

There is one more complication to the electron shells. Inside the shells themselves, electrons can be found in regions called orbitals. There are four types of orbitals—s, p, d, and/—and each has a specific shape. Blocks of the periodic table correspond to the different orbitals. The electrons in atoms of the first row of the table are found in the Is orbital. Helium, at the far right of the first row, consists of 2 electrons in the Is orbital. Neon, at the far right of the second row, has two electrons in the Is orbital, 2 electrons in the 2s orbital, and 6 electrons in the 2p orbital. These arrangements of electrons within orbitals are known as electron configurations. Chemists notate the electron configuration of helium as Is2 and neon as ls22s22p6. 

It is an unfortunate fact of life that there is another notation for two-electron integrals over spin orbitals in common use, particularly in the literature of Hartree-Fock theory. This notation, often referred to as the chemists notation, is... 

In this section, we will use the physicists notation for two-electron integrals rather than the chemists notation, which we used extensively in Chapter 3. We do this not out of perversity or even laziness but because almost all the literature in this area uses this notation, and we believe that one should develop equal facility with both notations. Recall that in the physicists notation... 

Calcium sulphoaluminate cements These are made from clinkers that include ye elimite (Ca4(A102)gS04 or C4A3 in Cement chemist notation) as a primary... 

Wiswesser line notation The Wiswesser line-formula notation (WLN) is a method for expressing the more usual graphical structure of a chemical compound as a linear string of symbols. The resulting alternative notation is unambiguous, short and particularly suitable for computer processing and retrieval but can also be understood easily by chemists after minimal training in its use. 

The first line notations were conceived before the advent of computers. Soon it was realized that the compactness of such a notation was well suited to be handled by computers, because file storage space was expensive at that time. The heyday of line notations were between I960 and 1970, A chemist, trained in this line notation. could enter the code of large molecules faster than with a structure-editing program,... 

The ROSDAL syntax is characterized by a simple coding of a chemical structure using alphanumeric symbols which can easily be learned by a chemist [14]. In the linear structure representation, each atom of the structure is arbitrarily assigned a unique number, except for the hydrogen atoms. Carbon atoms are shown in the notation only by digits. The other types of atoms carry, in addition, their atomic symbol. In order to describe the bonds between atoms, bond symbols are inserted between the atom numbers. Branches are marked and separated from the other parts of the code by commas [15, 16] (Figure 2-9). The ROSDAL linear notation is rmambiguous but not unique. 

Conversion in both directions needs heuristic information about conjugation. It would therefore be more sensible to input molecules directly into the RAMSES notation. Ultimately, we hope that the chemist s perception of bonding will abandon the connection table representation of a single VB structure and switch to one accounting for the problems addressed in this section in a manner such as that laid down in the RAMSES model. 

Quantum chemists have devised efficient short-hand notation schemes to denote the basis set aseti in an ab initio calculation, although this does mean that a proliferation of abbrevia-liijii.s and acronyms are introduced. However, the codes are usually quite simple to under-sland. We shall concentrate on the notation used by Pople and co-workers in their Gaussian aerie-, of programs (see also the appendix to this chapter). 

The electron configuration is the orbital description of the locations of the electrons in an unexcited atom. Using principles of physics, chemists can predict how atoms will react based upon the electron configuration. They can predict properties such as stability, boiling point, and conductivity. Typically, only the outermost electron shells matter in chemistry, so we truncate the inner electron shell notation by replacing the long-hand orbital description with the symbol for a noble gas in brackets. This method of notation vastly simplifies the description for large molecules. 

This chapter is in no way meant to impart a thorough understanding of the theoretical principles on which computational techniques are based. There are many texts available on these subjects, a selection of which are listed in the bibliography. This book assumes that the reader is a chemist and has already taken introductory courses outlining these fundamental principles. This chapter presents the notation and terminology that will be used in the rest of the book. It will also serve as a reminder of a few key points of the theory upon which computation chemistry is based. 

Chemists frequently work with measurements that are very large or very small. A mole, for example, contains 602,213,670,000,000,000,000,000 particles, and some analytical techniques can detect as little as 0.000000000000001 g of a compound. For simplicity, we express these measurements using scientific notation thus, a mole contains 6.0221367 X 10 particles, and the stated mass is 1 X 10 g. Sometimes it is preferable to express measurements without the exponential term, replacing it with a prefix. A mass of 1 X 10 g is the same as 1 femtogram. Table 2.3 lists other common prefixes. 

This is known as the physicist s notation, where the ordering of the functions is given by the electron indices. They may also be written in an alternative order with both functions depending on electron 1 on the left, and the functions depending on electron 2 on the right this is known as the Mulliken or chemist s notation. 

These alternative notations, and =, are used by chemists interchangeably in equations for chemical reactions. Both notations will be seen. 

The transition state for the first example1 contains the three constituents and bears a 3- charge. A correct but not particularly helpful notation is to denote its composition as [FeCsN7H403 nH20]. The chemical sense demands that the Fe(CN)5 core remain intact. It is the provenance of inorganic chemists to explore the situation further,... 

Since carbon has four bonds to fill, and because hydrogen is the most likely atom to be attached to carbon in an organic molecule, chemists invented a shorthand notation that is easier to read and draw. 

Chemists use a special notation to specify the structure of electrode compartments in a galvanic cell. The two electrodes in the Daniell cell, for instance, are denoted Zn(s) Zn2+(aq) and Cu2+(aq) Cu(s). Each vertical line represents an interface between phases—in this case, between solid metal and ions in solution in the order reactant product. 

Concentrations are used so frequently in chemistry that a shorthand notation for concentration is almost essential. Chemists represent the molar concentration of a species by enclosing its formula in brackets ... 

As the number of electrons In an atom Increases, a listing of all quantum numbers quickly becomes tedious. For example. Iron, with 26 electrons, would require the specification of 26 sets of 4 quantum numbers. To save time and space, chemists have devised a shorthand notation to write electron configurations. The orbital symbols (1 5, 2 p,... 

Chemists use logarithmic notation to express this huge range of concentrations. As one example. 

As usual, Feynman was right. His little particles captures an essential fact about atoms. They are tiny—so tiny that a teaspoon of water contains about 500,000,000,000,000,000,000,000 of them. Handling numbers this big is awkward. Try dividing it by 63, for example. To accommodate the very large numbers encountered in counting atoms and the very small ones needed to measure them, chemists use the scientific notation system. 

An analogous equation holds for the spin-down Fock matrix. The two-electron integrals in round brackets are defined by chemist s (11122) rather than the usual physicist s (12112) notation as ... 

The acid version of the cell was patented in 1866 by the French chemist George Leclanche, and is shown schematically in Figure 6.14 (A). The cell, in shorthand notation, corresponds to ... 

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