Sodium diatomic molecule, 288

Meier C and Engel V 1995 Pump-probe ionization spectroscopy of a diatomic molecule sodium molecule as a prototype example Femtosecond Chemistry Proc. Berlin Conf Femtosecond Chemistry (Berlin, March 1993) (Weinheim Verlag Chemie)... 

The first column of the periodic table, Group 1, contains elements that are soft, shiny solids. These alkali metals include lithium, sodium, potassium, mbidium, and cesium. At the other end of the table, fluorine, chlorine, bromine, iodine, and astatine appear in the next-to-last column. These are the halogens, or Group 17 elements. These four elements exist as diatomic molecules, so their formulas have the form X2 A sample of chlorine appears in Figure EV. Each alkali metal combines with any of the halogens in a 1 1 ratio to form a white crystalline solid. The general formula of these compounds s, AX, where A represents the alkali metal and X represents the halogen A X = N a C 1, LiBr, CsBr, KI, etc.). 

The equation states that elementary sodium reacts with elementary chlorine to produce sodium chloride, table salt. (The fact that chlorine is one of the seven elements that occur in diatomic molecules when not combined with other elements is indicated.) The numbers before the Na and NaCI are coefficients, stating how many formula units of these substances are involved. If there is no coefficient in a balanced equation, a coefficient of 1 is implied, and so the absence of a coefficient before the Cl2 implies one Cl2 molecule. The equation thus states that when the two reagents react, they do so in a ratio of two atoms of sodium to one molecule of chlorine, to form two formula units of sodium chloride. In addition, it states that when the two reagents react, they do so in a ratio of 2 mol of sodium to 1 mol of chlorine molecules, to form 2 mol of sodium chloride. The ratios of moles of each reactant and product to every other reactant or product are implied ... 

We have already discussed the importance of rotational excitation. It could well be the reason for the observed difference between polar and nonpolar diatomic molecules. Polar molecules exposing the sodium to a strongly nonisotropic potential may be rotationally excited much more easily, thus leading to a broader energy distribution after the quenching process. We continue this argument in Section VI. 

Except for the inert gases, atoms tend to interact with other atoms to form molecules. Hydrogen, oxygen, and nitrogen each readily form simple diatomic molecules. Invariably, molecules have properties that are quite different from those of the constituent elements. For example, a molecule of sodium chloride contains one atom of sodium (Na) and one atom of chlorine (Cl). Sodium is a highly reactive silvery metal, whereas chlorine is a corrosive yellow gas. When equal numbers of Na and Cl atoms interact, vigorous reaction occurs and white crystalline solid sodium chloride is formed. 

Chlorine (Cl) Chlorine, like bromine, is a diatomic molecule, Cl2. Chlorine is a toxic green gas that has excellent disinfectant properties. Chlorine gas dissolves in sodium hydroxide to give sodium hypoclorite (NaOCl), which you probably know as Clorox . 

Fluorine (F) Fluorine is a yellowish, poisonous gas. In its natural state it is a diatomic molecule, F2. Sodium fluoride is added to drinking water to strengthen teeth. Other fluoridation sources include sodium monofluoro-phosphate and stannous fluoride. The polymer of tetrafluoroethylene is a strong, slippery solid known as Teflon . 

The elementary substance sodium is at ordinary temperatures a soft, white metal. It consists of sodium atoms arranged in a regular structure (Fig. 4-5) similar to that described for copper, but not identical with it. The elementary substance chlorine is a greenish-yellow gas, consisting of diatomic molecules, Gig. Sodium metal will burn in chlorine gas, to give a new substance, which is sodium chloride (com mon salt), with properties greatly different from those of either of the two substances from which it is made. The sodium atoms in the sodium metal which reacted and the chlorine atoms in the chlorine gas which reacted are present in the sodium chloride formed by the reaction, but rearranged and ordered in a new way. 

The value of the periodic system is clearly illustrated by the halogens. All four of the elementary substances form diatomic molecules X2 their hydrogen compounds all have the formula HX, and their sodium salts the formula NaX. The free elements are all oxidizing agents, and their oxidizing power decreases regularly in the order Fg, CI2, Brg, I2. 

Sodium, energy bands as a function of atomic spacing, 179-180 sp hybrid orbital, features, 144 sp hybrid orbital, features, 144 sp hybrid orbital, features, 144-146 Spectroscopic constants asynunetric rotors, 229 diatomic molecules, 227 electronic excitation, see Electronic excitation... 

Figure 2.5 is a contour diagram of the charge density of the sodium chloride diatomic molecule overlaid with trajectories of Vp to illustrate the following general properties. 

Chapter 1 deals with the kinetics of the dissociation of diatomic molecules and the recombination of atoms, and Chapters 2 and 3 with the reactions of atoms and radicals with molecules, abstraction (metathetical) processes and addition to double and triple bonds. Data for the reactions of metal atoms with a variety of inorganic, organic and metal organic compounds, derived from sodium flame and molecular beam techniques, are discussed in Chapter 4 and rapid substitution at labile metal ions in solution in Chapter 5. The theory of, and the experimental results for, ion-molecule reactions, i.e. chemical processes resulting from binary collisions of positive or negative ions with neutral molecules, are discussed in Chapter 6 and the reactions of solvated electrons in Chapter 7. 

E. Bauer, E. R. Fisher, and F. R. Gilmore, De-excitation of Electronically Excited Sodium by Nitrogen and Some Other Diatomic Molecules, IDA p-471, March 1969. 

Several other elements, in addition to hydrogen, nitrogen, and oxygen, exist as diatomic molecules. For example, when sodium chloride is melted and subjected to an electric current, chlorine gas is produced (along with sodium metal). This chemical change is represented in Figure 3.12. Chlorine gas is a pale green gas that contains CI2 molecules. 

The vapours of metals are, as we have seen, quite different from the solids and liquids. In general, metals vaporize into a mixture of atoms and diatomic molecules, the proportion of the latter diminishing with increase of temperature. Thus, sodium metal just above the boiling point contains about 99% of sodium atoms and 1% of Na2 molecules. On vaporization of a metal, therefore, the individual ions or pairs of ions become separated from each other, carrying their electrons with them. The mechanism for the conduction of electricity accordingly breaks down, and metallic properties disappear. 

The electron affinities of homo-nuclear diatomic molecules are listed in Table SI.3. Like isolated atoms, most molecules have positive A. The exceptions are H2 and N2, adding an electron to which requires an expense of energy. The electron affinities of hetero-atomic molecules can reveal the location of the negative charge (the added electron) and sometimes the bond polarity. Thus, for the NaF, NaCl, NaBr and Nal, A = 0.520, 0.727, 0.788 and 0.865 eV, respectively. A comparison with the A of the Na2 and the corresponding X2 molecules indicates that in NaX the electron is added to the sodium atom, and the magnitude of A depends on the polarizability a and the bond distance d [49],... 

The small magnetic hfs in the E state of a homonuclear diatomic molecule is caused by the interaction of the nuclear spins / with the weak magnetic field produced by the rotation of the molecule. For the Nai molecular ground state the hyperfine splittings are smaller than the natural linewidth of the optical transitions. They could nevertheless be measured by the laser version of the Rabi technique [10.21]. A polarized argon laser beam at A, = 476.5 nm crosses the sodium beam and excites the Na2 molecules on the transition X = 0, 7" = 28) n (v = 3,7 = 27). The hfs... 

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