Princeton's WordNet(0.00 / 0 votes)Rate this definition: geological time, geologic time(noun) the time of the physical formation and development of the earth (especially prior to human history)
Ionic radius, r ion, is the radius of an atom's ion.Although neither atoms nor ions have sharp boundaries, they are sometimes treated as if they were hard spheres with radii such that the sum of ionic radii of the cation and anion gives the distance between the ions in a crystal lattice.herefore, the distance between the Na + and Cl â ions is half of 564.02 pm, which is 282.01 pm. However, although X-ray crystallography gives the distance between ions, it doesn't indicate where the boundary is between those ions, so it doesn't directly give ionic radii.
In an ionic solid, the ions are packed together into a repeating array called a crystal lattice. The concept of crystal packing assumes that the ions are hard spheres. The easiest way to picture such an array is to arrange one layer of spheres and then place successive layers over it.he packing arrangement adopted by an ionic compound is determined by the comparative sizes of the ions. Consider a lattice in which the anions assume a cubic array. The diagram below shows four spheres represent some anions of a part of a cubic layer. The dashed circle represents the anions below and above the plane.