Individual atomic ions

The first-formed individual atoms (ions or molecules) of B cannot be regarded as a distinct and separate phase but initially, at least, are expected to tend to conform to the structure of, and retain their former positions with reference to, the reactant phase A. During the continued accumulation of atoms (ions or molecules) of B, the consequent increase in total deformation strain energy will lead to a transformation to the structure characteristic of the stable product, solid B. This is quantitatively expressed [28] as a change in free energy by... 

Point defects are changes at atomistic levels, while line and volume defects are changes in stacking of planes or groups of atoms (molecules) m the structure. Note that the curangement (structure) of the individual atoms (ions) are not affected, only the method in which the structure units are assembled. Let us now examine each of these three types of defects in more detail, starting with the one-dimensional lattice defect amd then with the multi-dimensional defects. We will find that specific types have been found to be associated with each t3rpe of dimensional defect which have specific effects upon the stability of the solid structure. 

Not only masses bnt qnantities of substances in any units can be used for stoichiometry purposes. The quantities given must be changed to moles. Just as a mass is a measure of the number of moles of a reactant or product, the number of individual atoms, ions, or molecules involved in a chemical reaction may be converted to moles of reactant or product and used to solve problems. The number of moles of individual atoms or ions of a given element within a compound may also be used to determine the number of moles of reactant or product. The density of a substance may be used to determine the mass of a given volume of it and the mass may be used to determine the number of moles present. Some of these additional relationships are illustrated in Figure 10.3. 

Unlike compounds, mixtures can be separated by physical means into their components. A heterogeneous mixture has a non-uniform composition with visible boundaries between the components. A homogeneous mixture (solution) has a uniform composition because the components (elements and/or compounds) are mixed as individual atoms, ions, or molecules. 

Recall from Chapter 2 that a mixture has two defining characteristics its composition is variable, and it retains some properties of its components. In this chapter, we focus on solutions, the most common type of mixture. A solution is a homogeneous mixture, one with no boundaries separating its components thus, a solution exists as one phase. A heterogeneous mixture has two or more phases. The pebbles in concrete or the bubbles in champagne are visible indications that these are heterogeneous mixtures. In some cases, the particles of one or more components may be very small, so distinct phases are not easy to see. Smoke and milk are heterogeneous mixtures with very small component particles and thus no visible distinct phases. The essential distinction is that in a solution all the particles are individual atoms, ions, or small molecules. 

Heteroatomic molecules or individual atoms (ions) of two or more kinds... 

A homogeneous mixture (or solution) has no visible boundaries because the components are individual atoms, ions, or molecules. Thus, its composition is uniform. A mixture of sugar dissolved in water is homogeneous, for example, because the sugar molecules and water molecules are uniformly intermingled on the molecular level. We have no way to tell visually whether a sample of matter is a substance (element or compound) or a homogeneous mixture. 

A solution is a homogeneous mixture in which a solute dissolves in a solvent, and the separate particles occur as individual atoms, ions, or molecules. Solubility refers to the amount of solute that dissolves in a fixed amount of solvent at a given temperature. Intermolecular forces occur between solute and solvent particles, and the like-dissolves-like rule refers to the fact that solutions form when solute and solvent have similar types and strengths of intermolecular forces. Solutions occur with substances in any combination of physical states. (Section 13,1)... 

If electron-phonon interactions proceed along the substrate s surface or approach the surface from beneath, these interactions can induce further emissions from the periphery of the vaporized region. Owing to the lower energies involved, these emissions can be in the form of complete intact molecular species. This spike-based mechanism differentiates itself from cooperative motion by the fact that the former describes a superposition of events by individual atoms/ions making up the lattice, i.e. overlapping collisions within a single collision cascade, as opposed to a cooperative motion of many adjacent atoms. 

Since the exact masses of individual atomic ions are known with high accuracy, the exact mass of an ion of a given empirical formula (a known combination of atoms) is also known with high accuracy by simple summation. In mass spectrometry, measurement of the exact mass of an ion is used to deduce information about the empirical formula (not the molecular formula) of the ion. If the total number of possible combinations is small, and the measurement of the exact mass sufficiently accurate, the measurement can be used to derive an ion empirical formula. The traditional exact mass measurement is usually limited to the more abundant ions observed in the mass spectrum, since higher mass resolution in sector instruments was achieved at the cost of lower ion signal. 

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