The important bond chemicals linkage which hold together the components of crystalline solids and their general characteristics may be summarized as follows:
1. Ionic Linkages or ionic bond
In which the crystals are made up of regular geometrical arrangements of positive and negative ions. Such solids tend to possess high melting and boiling points, are hard and difficult to deform, and tend to be soluble in polar solvents. When dissolved in such solvents as fused, they are excellent conductors. Crystals characterized by such linkages are called ionic crystals. The salts are examples.
2. Covalent Linkages
In which the crystals are made up of molecules produced by the sharing of electrons, usually to pairs, between atoms of the elements involved. Such solids posses properties essentially opposite from those outlined for ionic crystals, although the partial ionic characters of many covalent bonds effect corresponding modifications. The following types of covalent crystalline solids may be distinguished.
In which mobile electrons provide the necessary forces for crystal stability. Such solids are characterized by toughness, malleability, ductility, high conductivity, luster, and insolubility in liquids other than molten metals. Any metal would be an example.
1. Ionic Linkages or ionic bond
In which the crystals are made up of regular geometrical arrangements of positive and negative ions. Such solids tend to possess high melting and boiling points, are hard and difficult to deform, and tend to be soluble in polar solvents. When dissolved in such solvents as fused, they are excellent conductors. Crystals characterized by such linkages are called ionic crystals. The salts are examples.
2. Covalent Linkages
In which the crystals are made up of molecules produced by the sharing of electrons, usually to pairs, between atoms of the elements involved. Such solids posses properties essentially opposite from those outlined for ionic crystals, although the partial ionic characters of many covalent bonds effect corresponding modifications. The following types of covalent crystalline solids may be distinguished.
- Non Polar molecular crystals, where weak attractive forces resulting from electronic motions are responsible for crystal stability. Such crystals are soft and easily melted or vaporized. Solid hydrogen, solid helium, and solid carbon tetrachloride are examples.
- Polar molecular crystals, where orientation of dipoles result in somewhat greater attractive forces and consequent increases in crystal stability. Although such materials are non-conductors, they do have enhanced melting points, boiling points, and solubilities in polar solvents over strictly non-polar crystals. Solid water, hydrogen chloride, etc. are examples.
- Atomic crystals, where three dimensional covalent bonding results in giant molecules. Such crystals are resistant to deformation and are often harder and higher melting than ionic crystals. Diamond, silicon carbide, etc. are examples.
In which mobile electrons provide the necessary forces for crystal stability. Such solids are characterized by toughness, malleability, ductility, high conductivity, luster, and insolubility in liquids other than molten metals. Any metal would be an example.
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