Covalent bonds solids held together

I2 is a molecular solid, held together by covalent bonds. 

Comparing polarity between components is often a good way to predict solubility, regardless of whether those components are liquid, solid, or gas. Why is polarity such a good predictor Because polarity is central to the tournament of forces that underlies solubility. So solids held together by ionic bonds (the most polar type of bond) or polar covalent bonds tend to dissolve well in polar solvents, like water. 

In every example seen so far the covalent bonds have held atoms together in order to make molecules. However, there exist substances such as diamond and graphite where the carbon atoms are covalently bonded but do not bond to form molecules. Such cases are called network solids the atoms bond to each other in a continuous network. The large network gives these solids a very high melting point. Also note that because both diamond and graphite are made up of the same element and are different substances, they are labeled allotropes of each other. 

In addition to symmetry, the nature of the bonding forces between atoms provides a useful way to classify solids. This classification does indeed lead to an understanding of the remarkable differences in the chemical and physical properties of different materials. We now consider crystals held together through ionic, metallic, or covalent bonding interactions, and the one class of solids held together by intermolecular forces. 

Platonic solids (see KeplePs Harmonices Mundi, Fig. 4) Platonic solids held together by strong covalent bonds have been known for some time. In white phosphorus (P ), the atoms occupy the corners of a tetrahedron." How did the ancients know that the tetrahedron was appropriate for fire and also for fiery white phosphorus Starting almost 40 years ago, clever organic chemists laboriously Tricked nature, seemingly thwarted" entropy, and assembled cubes, dodecahe-dra, and tetrahedra of covalently attached carbons. Nature, however, had its... 

The of solids mainly depends on the strength of interaction between its constituent atoms. For solids in which atoms are held together by weak van der Waals forces, a thermal expansivity of the order of 10 is found. On the other hand for covalently bonded solids like diamond, thermal expansivity of the order of 10 is reported. In case of polymers, constituent atoms are covalently bonded along the chain direction and perpendicular to the chain, the weak van der Waals interaction exists in between the chains. Hence, a large anisotropy in thermal expansivity is expected in crystalline and drawn polymers [32]. 

The lattice particles in solid silicon dioxide are individual atoms of silicon and oxygen. They are held together in the lattice by covalent bonds. Solids of this type are called network solids, and when such solids are melted or vaporized, strong covalent bonds must be broken. 

All polymers, if really solid, should have moduli above the lowest level we have calculated - about 2 GN m - since they are held together partly by Van der Waals and partly by covalent bonds. If you take ordinary rubber tubing (a polymer) and cool it down in liquid nitrogen, it becomes stiff - its modulus rises rather suddenly from around lO GNm" to a proper value of 4GNm . But if you warm it up again, its modulus drops back to 10 GNm . ... 

Several oxides and sulfides display the characteristics of network solids. The bond network of silica appears in Section 9-. Other examples are titania (Ti02) and alumina (AI2 O3). These two substances have extremely high melting points because their atoms are held together by networks of strong a covalent bonds. Like graphite, M0S2 is a two-dimensional network solid that serves as a solid lubricant. 

This relationship is illustrated in Figure 1. The science of solids is the science of supramolecular systems in which the three-dimensional solid structure is held together by covalent bonds... 

Chlorine gas is very reactive, and causes horrific bums to the eyes and throat see p. 243. The two atoms are held together by means of a single, non-polar covalent bond. CI2 has a yellow-green colour and, for a gas, is relatively dense at s.t.p. Conversely, table salt (sodium chloride) is an ionic solid comprising Na+ and Cl- ions, held together in a three-dimensional array. What is the reason for their differences in behaviour ... 

Finally, macromolecular covalent solids are unusual in comprising atoms held together in a gigantic three-dimensional array of bonds. Diamond and silica are the simplest examples see Figure 2.13. Giant macroscopic structures are always solid. 

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