Covalent atomic solid

Atomic solids are solids whose composite imits are individual atoms. Diamond (C), iron (Fe), and solid xenon (Xe) are good examples of atomic solids. Atomic solids can themselves be divided into three categories—covalent atomic solids, nonbonding atomic solids, and metallic atomic solids—each held together by a different kind of force ( Figure 12.28). 

Network covalent atomic solids, such as diamond, graphite, and silicon dioxide, are held together by covalent bonds. The crystal structures of these solids are more restricted by the geometrical constraints of the covalent bonds (which tend to be more directional than intermolecular forces, ionic bonds, or metallic bonds) so they do not tend to form closest-packed structures. 

Silicates (found in rocks, clays, and soils) are covalent atomic solids that contain silicon, oxygen, and various metal atoms. 

Network covalent Atoms — Covalent bond Hard solids with very high melting points noncon- C... 

Metals conduct electricity because their valence electrons move easily from atom to atom. Most covalently bonded solids do not conduct electricity, because their valence electrons are locked into individual bonds and are not free to... 

In covalent network solids, covalent bonds join atoms together in the crystal lattice, which is quite large. Graphite, diamond, and silicon dioxide (Si02) are examples of network solids. The crystal is one giant molecule. 

B—Diamond is a covalent network solid with a large number of strong covalent bonds between the carbon atoms. 

Fig.l Two layers of squaric acid crystal at room temperature, one is filled the other one is clear. Large circles represent oxygen, medium circles carbon and small circles hydrogen atoms. Solid heavy lines indicate covalent bonds while solid thin lines indicate hydrogen bonds. This representation refers to four unit cells [5]... 

The concepts which we need for understanding the structural trends within covalently bonded solids are most easily introduced by first considering the much simpler system of diatomic molecules. They are well described within the molecular orbital (MO) framework that is based on the overlapping of atomic wave functions. This picture, therefore, makes direct contact with the properties of the individual free atoms which we discussed in the previous chapter, in particular the atomic energy levels and angular character of the valence orbitals. We will see that ubiquitous quantum mechanical concepts such as the covalent bond, overlap repulsion, hybrid orbitals, and the relative degree of covalency versus ionicity all arise naturally from solutions of the one-electron Schrodinger equation for diatomic molecules such as H2, N2, and LiH. 

Carbon exists in more than 40 known structural forms, or allotropes, several of which are crystalline but most of which are amorphous. Graphite, the most common allotrope of carbon and the most stable under normal conditions, is a crystalline covalent network solid that consists of two-dimensional sheets of fused six-membered rings (Figure 10.26a). Each carbon atom is sp2-hybridized and is connected to three other carbons. The diamond form of elemental carbon is a covalent network solid in which each carbon atom is sp3-hybridized and is bonded with tetrahedral geometry to four other carbons (Figure 10.26b). 

Solids can be characterized as amorphous if their particles are randomly arranged or crystalline if their particles are ordered. Crystalline solids can be further characterized as ionic solids if their particles are ions, molecular solids if their particles are molecules, covalent network solids if they consist of a covalently bonded array of atoms without discrete molecules, or metallic solids if their particles are metal atoms. 

Silicon nitride (Si3N4), a high-temperature ceramic useful for making engine components, is a covalent network solid in which each Si atom is bonded to four N atoms and each N atom is bonded to three Si atoms. Explain why silicon nitride is more brittle than a metal like copper. 

The atoms in network atomic solids are held together by forces created when electrons are shared between atoms. These forces create a type of chemical bond known as a covalent bond. 

Sometimes atoms or molecules can form covalent bonds with many other atoms or molecules to make huge structures that can be seen. These are called network atomic solids and can form when a covalent bond occurs between many atoms or molecules at the same time. 

The hardest network atomic solid—in fact, the hardest (currently) known material on the planet—is a type of carbon that forms diamonds. The covalently bonded arrangement of carbon atoms within diamonds forms naturally at intense temperatures and pressures inside the Earth. 

Covalent network solids contain atoms held together by a network of covalent bonds that link every atom in the solid to every other atom. The molecules are gigantic each particle of the crystal is essentially one molecule. This type of solid is hard, nonvolatile, with a very high melting point and insoluble in both water and inorganic solvents. They do not conduct electricity. 

Covalent or Polymeric Solids In such solids covalent bonds extend throughout the solid and so they may be considered as very large molecules, e.g. diamond, graphite, etc. They are also known as atomic solids. 

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