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Thus, some aspect of zinc sulfide makes it more favorable for the zinc to be surrounded by only four anions (it is believed that the relative size of the cation and anion determine the coordination number). Part (b) of this figure focuses in on a smaller part of the lattice so that we can see a sodium ion (the silver sphere in the center) surrounded by chloride ions. Figure 43 shows a photo of the sodium chloride lattice (a lattice is just a regular, systematic arrangement of particles). These ions are packed very efficiently to make the best use of the available space and to maximize the number of ions of opposite charge that surround a particular ion. As we know from our previous discussion of bonding, ionic compounds consist of ions. There four basic types of solids: a) ionic, b) molecular, c) covalent network, and d) metallic. Let's deal first with the nature of the substance. Hence, it appears that there are two factors-the nature of the substance and the temperature-that determine in what state it exists. We also know that any substance can be vaporized if the temperature is high enough. We are familiar with the three states in which water exists-as ice up to its melting point of 0 ☌, as a liquid between 0 and 100 ☌, and as a gas (steam) above 100 ☌. At this point you are probably wondering why some substances exist in the solid state, whereas others exist in the liquid or gaseous states at room temperature.