Saturday, May 14, 2011

Characteristics of Covalent Compounds

The general characteristics of covalent compounds are as follows;
(i).     Gases, Liquids or Solids at Room Temperature
        The covalent compounds are often gases, liquids or relatively soft solids under ordinary conditions. This is because of weak intermolecular forces between the molecules.
(ii).    Low Melting Points
        Covalent compounds have generally low melting points (or boiling points). The molecules are held together in the solid crystal lattice by weak forces. On application of heat, the weak forces are easily broken down and hence these compounds have low melting and boiling points.
(iii).    Neither Hard nor Brittle
        While the ionic compounds are hard and brittle, covalent compounds are neither hard nor brittle. There are weak forces holding the molecules in the solid crystal lattice. A molecular layer in the crystal easily slips over the adjacent layers. Thus the crystals are easily broken and there is no sharp cleavage between the layers on application of external force.
(iv).     Soluble in Organic Solvents
        In general, covalent compounds dissolve readily in non polar organic solvents (benzene, ether). The kinetic energy of the solvent molecules easily overcomes the weak intermolecular forces. Covalent compounds are insoluble in water. Some of them (alcohols, amines) dissolve in water due to hydrogen bonding.
(v).    Non-Conductors of Electricity
        Since there are no cations or anions in covalent molecules, the covalent compounds in the molten or solution form are incapable of conducting electricity.
(vi).    Exhibit Isomerism
        Covalent bonds are rigid and directional, the atoms being held together by shared electron pair and not by electrical lines of force. This gives opportunity for various spatial arrangements and covalent compounds exhibit stereo-isomerism.
(vii).    Molecular Reactions
        The covalent compounds don't have ions and hence these reactions are slow.

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