Covalent Network Solid
A covalent network solid is a type of solid in which the atoms are bonded together by a network of covalent bonds, forming a continuous three-dimensional structure. This results in a strong and rigid solid with high melting and boiling points. Examples of covalent network solids include diamond, graphite, and silicon dioxide (quartz).
5 Key excerpts on "Covalent Network Solid"
eBook - ePub- Jeffrey Gaffney, Nancy Marley(Authors)
- 2017(Publication Date)
- Elsevier(Publisher)
...While brittle solids fracture immediately when enough stress is applied, ductile solids undergo a period of deformation followed by fracture. The intermolecular forces in many molecular solids are directional, leading to mechanical properties that vary with the direction of the applied stress. Molecular solids are usually insulators because the localization of electrons in the covalent bonds of the molecules prevents their movement in the crystal lattice. However, if an alkali metal is intercolated into the crystal lattice voids, the valence electrons on the alkali metal can be easily ionized allowing them to move freely in the crystal lattice. This gives the molecular solid electrical conductivity it would not otherwise have without significantly changing the other properties. 11.4 Atomic Solids Atomic solids, also called network solids, are composed of atoms connected by covalent bonds in a continuous network. There are two types of atomic solids: those that are totally composed of an extended three-dimensional covalent network and those that are composed of two-dimensional covalent networks, which are held together by weaker van der Waals forces (mixed bonding). In the three-dimensional networks, the covalent bonding extends throughout the solid and the result is a macroscopic interlocking covalent lattice structure. Any distortion of the crystal geometry can only occur through breaking the strong covalent bonds. In the two-dimensional networks, distortion of the three-dimensional geometry is more easily accomplished by disturbing the weaker intermolecular forces holding the two-dimensional planes together. The most common examples of atomic solids are the allotropes of carbon. These allotropes, different solid forms of carbon, are shown in Fig. 11.9. The two most common allotropes of carbon are diamond and graphite...
eBook - ePubChemistry
Concepts and Problems, A Self-Teaching Guide
- Richard Post, Chad Snyder, Clifford C. Houk(Authors)
- 2020(Publication Date)
- Jossey-Bass(Publisher)
...In the liquid state, the crystal lattice is broken and the ions are free to move about and carry the electric current. Most ionic solids dissolve easily in water. The aqueous solutions of ionic solids also conduct electricity well. A very hard solid with a high melting point dissolves in water, but the aqueous solution does not conduct electricity. Would you expect the solid to be ionic?_________________ Answer: no (Ionic solids dissolve readily in water and conduct electricity.) Covalent solids (also known as network solids) consist of atoms held together completely by covalent bonds extending from atom to atom throughout the crystal lattice. The entire crystal lattice is interlocked in a series of such covalent bonds. Covalent bonds are very strong, and such solids are very hard with very high melting points. A relatively large amount of energy is required to break the bonds. A solid substance with a high melting point could be (an ionic solid, a covalent solid, either an ionic solid or a covalent solid) _______________ Answer: either an ionic solid or a covalent solid (Covalent solids often have higher melting points than ionic solids, but both have relatively high melting points.) Covalent solids are nonconductors of electricity in either the solid or the molten (liquid) state. Most covalent solids are not soluble in water. Typical examples of covalent solids are diamond (made of carbon), silicon carbide (SiC, better known as carborundum), and aluminum nitride (AlN). All of these examples are useful as industrial abrasives for grinding and polishing because of their hardness. A solid is heated until it melts at a high melting point. The molten substance conducts electricity. This solid is likely to be (an ionic solid, a covalent solid, either an ionic or covalent solid) _____________________ Answer: an ionic solid (Ionic solids conduct electricity when molten, while covalent solids do not.) Molecular solids are made up of either polar or nonpolar molecules...
eBook - ePub- Tony Cox(Author)
- 2004(Publication Date)
- Taylor & Francis(Publisher)
...An imbalance of defects involving different elements can introduce nonstoichiometry. This is common in compounds of transition metals, where variable oxidation states are possible (see Topics D5 and H4). For example, the sodium tungsten bronzes are formulated as Na x WO 3, where x can have any value in the range 0–0.9. Another form of nonstoichiometry arises from the partial replacement of one element by another in a crystal. It is common in natural minerals, such as the aluminosilicate feldspars (Na,Ca)(Al,Si) 4 O 8. The notation (Na,Ca) means that Na and Ca can be present in the same crystal sites in varying proportions. Simultaneous (Si,Al) replacement ensures that all elements remain in their normal oxidation states. Even this formulation is approximate, as several other elements may be present in smaller proportions. Chemical Classification Solids are often classified according to their chemical bonding, structures and classification properties (see Topic B1): Molecular solids contain discrete molecular units held by relatively weak inter-molecular forces (see Topic C10). Metallic solids have atoms with high coordination numbers, bound by delocalized electrons that give metallic conduction. Covalent or polymeric solids have atoms bound by directional covalent bonds, giving relatively low coordination numbers in a continuous one-, two- or three-dimensional network. Ionic solids are bound by electrostatic attraction between anions and cations, with structures where every anion is surrounded by cations and vice versa. Although these broad distinctions are useful, many solids show a degree of intermediate character, or even several types of bonding simultaneously. Metallic and covalent interactions both arise from overlapping atomic orbitals (see Topics C4 – C7) and the distinction in physical properties arises from the energy distribution of electronic levels (see Topic D7)...
eBook - ePub- Milton Ohring(Author)
- 2001(Publication Date)
- Academic Press(Publisher)
...Other largely ionic film materials of note include MgF 2 and ZnS for use in optical coatings, YBa 2 Cu 3 O 7 high-temperature superconductors, Al 2 O 3 for hard coatings, and assorted thin-film oxides such as Y 3 Fe 5 O 12 and LiNbO 3, used respectively in magnetic and integrated optics applications. Transparent electrical conductors such as In 2 O 3 –SnO 2 glasses, which serve as heating elements in window defrosters on cars as well as electrical contacts over the light-exposed surfaces of solar cells, have partial ionic character. 1.4.3.3 Covalent Elemental as well as compound solids exhibit covalent bonding. The outstanding examples are the elemental semiconductors Si, Ge, and diamond, as well as III–V compound semiconductors such as GaAs and InP. Whereas elements at the extreme ends of the periodic table are involved in ionic bonding, covalent bonds are frequently formed between elements in neighboring columns. The strong directional bonds characteristic of the group IV elements is due to the hybridization or mixing of the 2s and 2p electron wave functions into a set of orbitals that have high electron densities emanating from the atom in tetrahedral fashion. A pair of electrons contributed by neighboring atoms comprises a covalent bond, and four such shared electron pairs complete the bonding requirements. Covalent solids are strongly bonded hard materials with relatively high melting points. Despite the great structural stability of semiconductors, relatively modest thermal stimulation is sufficient to release electrons from filled valence bonding states into unfilled conduction-electron states. We speak of electrons being promoted from the valence to conduction band, a process that increases the conductivity of the solid. Small dopant additions of group III elements such as B and In as well as group V elements such as P and As take up regular lattice positions within Si and Ge...
- Kevin Reel, Derrick C. Wood, Scott A. Best(Authors)
- 2014(Publication Date)
- Research & Education Association(Publisher)
...The partial charges are represented by the lower-case Greek symbol delta (δ). The element that has the greater electronegativity will be slightly negative (δ −) and the other element will be slightly positive (δ +). • Dipoles are molecules that contain polar covalent bonds that are not completely canceled out by other polar bonds. The polar bonds add together like vectors to create a total dipole moment on the molecule, which results in the molecule having separate centers of positive and negative charge. Network Covalent Bonding • Network covalent crystals are groups of nonmetal atoms held together by covalent bonds. • The bonding in a network covalent solid is extensive, and repeats throughout the crystalline structure. • Network covalent crystals tend to have very high melting and boiling points, and a large amount of energy is needed to break apart the crystal. • The most common example of a network covalent solid is a diamond, which is a network covalent crystal of sp 3 hybridized carbon atoms bonding to one another over and over again. (See Figure 6.1.) Figure 6.1. Structure of a Diamond TEST TIP Network covalent solids are usually the same type of atom bonded over and over again. Look for chemical formulas such as S 8 or C 60 or common names such as diamond or graphite. Metallic Bonds DID YOU KNOW? Graphite conducts electricity because the sp 2 hybridized orbitals allow for one double bond per carbon atom. This double bond is delocalized and moves freely through-out the structure, thus conducting electricity. In addition, the planar sheets of graphite move easily past one another which makes it a good lubricant. • Metals compose the majority of elements on the periodic table, and all elements to the left of the metalloids on the periodic table (except hydrogen) are metals. • Metallic bonding can be thought of as cations surrounded by a sea of electrons...
