الاجسام الصلبة - الطاقة الكيميائية .. الفيزياء

Solids - Chemical Energy .. Physics

Solids

Most solids, such as ice, are characterized by having a cohesive crystalline structure, that is, in other words, they have a specific melting point, which is the temperature required for the ions or atoms of the crystals to break the bonds between them. However, there is a class of solids that do not have a crystalline structure, and they are called amorphous bodies. These do not have a specific melting point - that is, they melt little by little as their temperature rises. Glass is the clearest example of this type of body.

A non-crystalline solid can be considered a superfluid fluid. Crystals in solids are of three types: electrical valence crystals, covalent valence crystals, and metallic crystals.

The first consists of ions that are held together by electrical valence bonds in an intertwined arrangement that does not limit their vibrations around fixed sites in it: Covalent valence crystals are characterized by being very easily dissolved in water due to the disintegration of the bonds between them and the release of ions inside the solution. It is known that most organic compounds belong to the first type of crystals, as each crystal consists of several molecules held together by weak forces called intermolecular forces. As for solid bodies, such as diamonds, they belong to the second type of crystals, and their atoms are linked to each other by strong covalent forces. As for metallic crystals, their atoms are scattered (ionized), and since they are composed of positive ions as a whole, there are no electrical valence forces in them like those found in the first type. As for the electrons that have vacated the metal layers, they become free in the crystal structures - that is, the metal ions are floating in a (gas) of electrons. Solids expand when heated due to the widening range of ion vibrations in the atoms of the crystal when its temperature rises. Each solid has a coefficient of thermal expansion that distinguishes it from others (which is the amount of expansion of a unit length when its temperature rises by one degree). This phenomenon must be taken into account in the construction of bridges and the extension of railways.

(Above) A tube of etched lead in which crystal grains can be seen. (Below) A cubic crystal network similar to the network of natural salt (S cl).