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Don't think of it so much as putting the center mass of an atom on a vertex but as matching the unit cell symmetry to the crystal symmetry. Take the definition from google below, I've bolded key parts: The smallest group of atoms of a substance that has the overall symmetry of a crystal of that substance, and from which the entire lattice can be built up ...


2

They actually form: ions can be dissolved up till a certain concentration, and beyond that, they form ionic lattices just as you predict. The easiest way to describe the scenario as an equilibrium between ions-in-water vs ions-in-lattice: If the ion-water interaction is very strong, the ions can be very stable in water, even more than in an ionic lattice, ...


1

The actual, "real" state of the atoms (and then ions) that combine to form an ionic compound is not particularly significant to the question at hand. When we want to calculate the lattice energy of an ionic compound, one method used is a Born-Haber Cycle. In essence, we use Hess' Law to combine a series of elementary steps that results in the overall ...


1

Between 273 K and 500 K the intrinsic carrier concentration in Si increases by about 5 orders of magnitude. Compare with the decrease in conductivity of a metal over that range. Increase in carriers far outweighs the increased scattering of carriers.


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Your statement 'For example, Na+ bonds with OH− and Cl− bonds with H+ when NaOH is dissolved in H2O' is not correct if the ions are in solution. In an ionic solid each ion is surrounded by other ions of the same charge and those of opposite charge, in NaCl each Na$^+$ ion is surrounded by 6 Cl$^-$ and vice versa. The interaction between the ions is ...


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Yes of course, if you do the math right, that limes gives the exact same number. Don't forget to look out for atoms that are completely within the unit cell.


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In answer to you first question, no if hkl differ, yes if they do not. I try to explain below. In a crystal the unit cell defines the repeating unit. Inside the unit cell the atoms are arranged as they are in the molecular structure with the molecule being at the same angle and position within each of the unit cells. Each atom scatters the x-ray radiation ...


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