Chlorine, atom/ions

This indicates that, in crystalline sodium chloride (for structure, click here http //bit.lv/gXzbqk or see Appendix 2), each sodium atom (ion) is surroimded by six chlorine atoms (ions), each of which is shared between six sodium atoms (ions), giving an empirical formula NaCl. Crystallographers call the munber of nearest neighbours the coordination number . 

Chemical formulas, which we defined in Section 1.3.2 as symbolic designations for compounds, are used for both molecular compounds and ionic compounds. Thus we can tell what elements are chemically combined to make up a compound by looking at its formula. Examples we presented in Section 1.3.2 included H2O (water), a combination of hydrogen (H) and oxygen (O), and NaCl (sodium chloride, or salt), a combination of sodium (Na) and chlorine (Cl). Water is an exanple of a molecular compound, while sodium chloride is an example of an ionic compound. Since compounds are composed of elements in chemical combination, it follows that molecules and formula units are composed of the atoms of the elements in chemical combination. Thus, molecules of water are composed of atoms of hydrogen in chemical combination with atoms of oxygen, and formula units of salt are composed of sodium atoms (actually ions) and chlorine atoms (ions) in chemical combination. It is the nature of this chemical combination that defines whether a compound is molecular or ionic. This will be detailed further as our study proceeds. 

An example of the Diabatic potential energy curves for the NaCl molecule is shown in Figure 3.39(a). This suggests that as the Sodium atom/ion separates from the Chlorine atom/ion, the potential curves representing the neutral and charged... 

The strongly electronegative (p. 49) chlorine atom becomes a chloride ion, the proton accepting the electron pair donated by the nitrogen atom. A similar reaction occurs when ammonia is passed into water, but to a much lesser extent as oxygen in water is a poorer donor of the electron pair ... 

Golddll) chloride dissolves in hydrochloric acid to form tetra-chlorauric acid. HAUCI4. Here again, the gold(III) is 4-co-ordinate in the ion [AuCl4] . If alkali is added to this acid, successive replacement of chlorine atoms by hydroxyl groups occurs, forming finally the unstable tetrahydroxoaurate IlI) ion, [Au(OH)4] ... 

Compounds that contain chlorine, bromine, sulfur, or silicon are usually apparent from prominent peaks at masses 2, 4, 6, and so on, units larger than the nominal mass of the parent or fragment ion. Eor example, when one chlorine atom is present, the P + 2 mass peak will be about one-third the intensity of the parent peak. When one bromine atom is present, the P + 2 mass peak will be about the same intensity as the parent peak. The abundance of heavy isotopes is treated in terms of the binomial expansion (a -I- h) , where a is the relative abundance of the light isotope, b is the relative abundance of the heavy isotope, and m is the number of atoms of the particular element present in the molecule. If two bromine atoms are present, the binomial expansion is... 

In a process similar to that described in the previous item, the stored data can be used to identify not just a series of compounds but specific ones. For example, any compound containing a chlorine atom is obvious from its mass spectrum, since natural chlorine occurs as two isotopes, Cl and Cl, in a ratio of. 3 1. Thus its mass spectrum will have two molecular ions separated by two mass units (35 -i- 2 = 37) in an abundance ratio of 3 1. It becomes a trivial exercise for the computer to print out only those scans in which two ions are found separated by two mass units in the abundance ratio of 3 1 (Figure 36.10). This selection of only certain ion masses is called selected ion recording (SIR) or, sometimes, selected ion monitoring (SIM, an unfortunate... 

Naturally occurring isotopes of any element are present in unequal amounts. For example, chlorine exists in two isotopic forms, one with 17 protons and 18 neutrons ( Cl) and the other with 17 protons and 20 neutrons ( Cl). The isotopes are not radioactive, and they occur, respectively, in a ratio of nearly 3 1. In a mass spectrum, any compound containing one chlorine atom will have two different molecular masses (m/z values). For example, methyl chloride (CH3CI) has masses of 15 (for the CH3) plus 35 (total = 50) for one isotope of chlorine and 15 plus 37 (total = 52) for the other isotope. Since the isotopes occur in the ratio of 3 1, molecular ions of methyl chloride will show two molecular-mass peaks at m/z values of 50 and 52, with the heights of the peaks in the ratio of 3 1 (Figure 46.4). 

Partial mass spectra showing the isotope patterns in the molecular ion regions for ions containing carbon and (a) only one chlorine atom, (b) only one bromine atom, and (c) one chlorine and one bromine atom. The isotope patterns are quite different from each other. Note how the halogen isotope ratios appear very clearly as 3 1 for chlorine in (a), 1 1 for bromine in (b), and 3 4 1 for chlorine and bromine in (c). If the numbers of halogens were not known, the pattern could be used in a reverse sense to decide their number. 

In this reaction, three steps, ie, acylation, cyclization, and replacement of the chlorine atom by the hydroxyl group, take place simultaneously in concentrated sulfuric acid. In the course of cyclization 2,7-dichlorofluoran (31) may be formed as a by-product presumably through the carbonium ion (30) ihustrated as follows. The addition of boric acid suppresses this pathway and promotes the regular cyclization to form the anthraquinone stmcture. The stable boric acid ester formed also enables the complete replacement of chlorine atoms by the hydroxyl group. Hydrolysis of the boric acid ester of quinizarin is carried out by heating in dilute sulfuric acid. The purity of quinizarin thus obtained is around 90%. Highly pure product can be obtained by sublimation. 

The archetype of the ionic ceramic is sodium chloride ("rocksalt"), NaCl, shown in Fig. 16.1(a). Each sodium atom loses an electron to a chlorine atom it is the electrostatic attraction between the Na ions and the CF ions that holds the crystal together. To achieve the maximum electrostatic interaction, each Na has 6 CF neighbours and no Na neighbours (and vice versa) there is no way of arranging single-charged ions that does better than this. So most of the simple ionic ceramics with the formula AB have the rocksalt structure. 

The stable sodium ion has a positive charge because it is short of one electron and the chlorine atom is negatively charged for the converse reason. Ionic bonds are seldom found in polymers of current interest as plastics materials although the ionic bond is important in ion-exchange resins and in the ionomers (see Chapter 11). 

Electropositive fluorinating agents are categorized in distinct classes as (1) fluoroxy reagents, in which the fluorine is bound to an oxygen atom (for reviews, see references 1,2,3, 4, 5, and 6) (2) fluoraza reagents, in which the fluorine atom IS bound to the nitrogen atom of either an amide or ammonium ion structure (for a partial review, see reference 6), (3) xenon difluoride, in which the fluorine atoms are bound to xenon (for reviews, see references 5, 7, 8, and 114) and (4) perchloryl Iluoride, in which the fluorine atom is bound to the chlorine atom of the perchloryl function (for a review, see reference 9). 

In this paper Speziale and Smith 109) described experiments which led them to modify the mechanism proposed earlier 108) for the reaction of trivalent phosphorus compounds with haloamides. The first step is considered to be attack of the trivalent phosphorus compound on a chlorine atom of the halo amide (132) to produce a resonance-stabilized enolate ion (133). This is reasonable since under conditions where the trichloroamide... 

When potassium chlorate solution, KClOi, is added to hydrochloric acid, chlorine gas is evolved. Although we can find the half-reaction, 2C1- = Ck(g) + 2e, in Appendix 3, we find no equation with CIQT ion involved. We can surmise that CIO3" is accepting electrons and changing into chlorine. Let us write a partial half-reaction in which we indicate an unknown number of electrons and in which we have conserved only chlorine atoms ... 

Notice that in an octahedral complex ion such as [Cr(NH3)4Cl2]+ there is a possibility of observing isomers. The two chlorine atoms may occupy octahedral positions which are next to each other on the same side of the metal atom, or positions located on opposite sides of the - metal atom (see Figure 22-4). The isomer in which the two similar groups are located on the same side of the metal atom is called the cis-isomer, and the other is called the trans-isomer. 

From the isotope abundances listed in Table 2.1, it is obvious that the M + 2 ion abundance in this example is due to two chlorine atoms. 

Dichloronitrotoluenes are indicated by the presence of an odd molecular ion with chlorine isotopes showing two chlorine atoms and losses of 30 and 46 Daltons. Again, when the chlorine atoms are on the benzene ring, the loss of chlorine from the molecular ion does not occur. An M - Cl ion indicates that at least one of the chlorines is on the alkyl group. 

The molecular ion must contain the highest number of atoms of each element present. For example, if a lower-mass ion contains four chlorine atoms, but the highest-mass ion observed contains only three, then at least 35 Daltons should be added to the highest-mass ion observed to deduce the molecular ion. 

The mass spectrum of the unknown compound showed a molecular ion at m/z 246 with an isotope pattern indicating that one chlorine atom and possibly a sulfur atom are present. The fragment ion at m/z 218 also showed the presence of chlorine and sulfur. The accurate mass measurement showed the molecular formula to be C]3FI7OSCl R + DB = 10. 

The presence of three chlorine atoms is easily determined by the isotope ratios. The odd molecular weight shows the presence of nitrogen. The loss of m/z 30 and 46 from the molecular ions shows the presence of the nitro group. 

The molecular ion for chlordane can be observed in Figure 25.1. Note the pattern for eight chlorine atoms. The most abundant fragment ion is the loss of a chlorine atom at m/z 373. 

The molecular ion is apparent in the mass spectrum of DDT (Figure 25.2) at m/z 352 with the classic isotope pattern for five chlorine atoms (see Appendix 11). The major fragment ion is the loss of CCI3 at m/z 235. 

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