Sodium chloride molecules

Fig. 3-5.—Energy curves for the sodium chloride molecule. At very large internuclear distances the curve for the ionic structure lies above that for the covalent structure. The curves cross at 10.5 A, and at smaller inter-nuclear distances the ionic structure is the more stable one ...

In 1956 Owe Berg (115) advocated the existence in water of hydrates involving as many as 60 molecules per sodium chloride. He correctly noted that 60 water molecules could not be bound directly to one NaCl molecule (quite apart from the fact that there are no sodium chloride molecules in the solution) and that the hydrates, therefore, are to be regarded as compositions of structural transformations. Horne and Birkett (81) have also suggested the existence of large numbers of hydration. Thus, estimates of 45-50 water molecules were obtained by different independent methods for lithium ion hydration. 

NaCI represents the compound containing one atom of sodium and one atom of chlorine. The masses on these elements are too small to determine individually or as individual ionic units. However, using the mole we can determine the mass of the compound represented by the formula NaCI. One mole of sodium atoms has a mass of 23.0 grams and one mole of chlorine atoms has a mass of 35.5 grams. Therefore, one mole of sodium chloride molecules has a mass of 58.5 grams. 

These two parts of the molecule of sodium chloride were absolutely free In solution the ions swam around m all directions. There were no longer any sodium chloride molecules present. Only sodium ions and chlorine ions peopled the water. Here was the crash of a holy idol. Clausius had said that only some of the molecules were in this peculiar condition of dismemberment. Young Svante, the beginner, had dared declare that all the molecules m dilute solutions were disrupted. 

The error involved in making this approximation amounts to only a few kcals for the sodium chloride molecule. This is negligible for our present purpose. The total energy of interaction of the ions is then given by,... 

The Kirkwood-Buff integrals Gn and G13 in the binary mixture water (1) -1- sodium chloride (3) were taken from reference [71]. The values obtained for G12 and G23 from Eqs. (27) and (28) were used to calculate the excesses (or deficits) number of water and sodium chloride molecules in the vicinity of a gas molecule. 

You are rescued by noticing that, if the sodium chloride molecule were formed in this way, the two ions would still be separated by a great distance. For the purpose of quantitative argument the formation of the ionic bond... 

Thermal agitation causes an alkali halide molecule to vibrate about its equilibrium length r0. Since it is then an oscillating dipole, it can interact with electromagnetic radiation. Use (3.1) and the results of Discussion 3.2 to calculate the vibration frequency of the sodium chloride molecule. In what range of the electromagnetic spectrum does this frequency lie ... 

Why is the term "sodium chloride molecule" incorrect but the term "carbon dioxide molecule" is correct ... 

Why is it not proper to speak of sodium chloride molecules What is a covalent bond How does it differ from an ionic bond Briefly comment on the stmcture Na 0 Na for the compound Na20. 

The metadynamics method was introduced in 2002 by Laio and Parrinello as an elegant extension of adaptive bias potential methods [65]. The authors used a coarse-grained non-Markovian dynamics in the space defined by a few collective coordinates s,. With the aid of a history-dependent potential term the minima of the FES were filled in time, allowing the efficient exploration and accurate determination of the FES as a function of the collective coordinates. Laio and Parrinello demonstrated the appUcabUity of this approach in the case of the dissociation of a sodium chloride molecule in water and in the study of the conformational changes of a dialanine in solution [65]. 

Distinguishing the Entities in Covalent and Ionic Substances There is a key distinction between the chemical entities in covalent substances and in ionic substances. Most covalent substances consist of molecules. A cup of water, for example, consists of individual water molecules lying near each other. In contrast, under ordinary conditions, there are no molecules in an ionic compound. A piece of sodium chloride, for example, is a continuous array in three dimensions of oppositely charged sodium and chloride ions, not a collection of individual sodium chloride molecules. ... 

Figures 12.2 and 12.3 should help you form a mental model of an ionic compound. A key characteristic of your mental model needs to be an image of the ion itself as an individual particle. There are no such things as sodium chloride molecules. The ionic compound sodium chloride consists of equal numbers of sodium ions and chloride ions, but there are no discrete sodium chloride units. Each positively charged sodium ion is surrounded by negatively charged chloride ions, and each chloride ion is surrounded by sodium ions.

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