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=== Molecular Compound ===

=== Molecular Compound ===

In contrast, the basic unit of a ''molecular compound'' is the ''molecule''--an object containing two or more [[atoms]] joined together by [[covalent bond|covalent bonds]]. ''A molecule is the smallest particle of a compound that retains the unique defining properties of that compound.'' A molecule never dissociates when it dissolves--or if it does, it might be transformed into a [[polyatomic ion]] by giving up an atom of [[hydrogen]]. (The weak organic [[acid|acids]] commonly behave this way.)

A ''molecular compound'' is a compound which is composed of atoms joined by [[covalent bond]]s. In contrast to the formula unit of ionic crystals, the basic unit of a molecular compound is the ''molecule''. A molecule is the smallest particle of a compound that retains the unique defining properties of that compound.

Molecules may be either ''polar'' or ''nonpolar''. Polar molecules have an unequal distribution of electric charge among their atoms, giving them distinct positive and negative "sides." (The charge on either "side" of a polar molecule is almost never equal to the full charge on, say, a single [[proton]] or [[electron]]. If it were, then the particle would be an ion.) Nonpolar molecules distribute their electrons evenly and thus have ''no'' partial positive or partial negative charge on any aspect of them.

Molecules may be either ''polar'' or ''nonpolar''. Polar molecules have an unequal distribution of electric charge among their atoms, giving them distinct positive and negative regions. The charge in any region of a polar molecule is almost never equal to the full charge on, say, a single [[proton]] or [[electron]]. If it were, then the particle would be an ion. Nonpolar molecules distribute their electrons evenly and thus have no partial positive or partial negative charge on any aspect of them.

In general, polar solutes dissolve in polar solvents, and nonpolar solutes dissolve in nonpolar solvents. Ionic compounds (see above) typically dissolve only in polar solvents.

In general, polar solutes dissolve in polar solvents, and nonpolar solutes dissolve in nonpolar solvents. Ionic compounds (see above) typically dissolve only in polar solvents.

Molecular compounds are also either ''organic'' or ''inorganic''. [[Organic compound|Organic compounds]] contain carbon; inorganic compounds do not. Polyatomic ions may also be organic or inorganic--though an organic polyatomic ion is usually a dissociated weak organic acid of the form R-COOH, where R is the rest, or ''residue'', of the molecule.

Molecular compounds are also either ''organic'' or ''inorganic''. [[Organic compound|Organic compounds]] contain carbon; inorganic compounds do not. Polyatomic ions may also be organic or inorganic -- though an organic polyatomic ion is usually a dissociated weak organic acid of the form R-COOH, where R is the rest, or ''residue'', of the molecule.

== Descriptors of Compounds ==

== Descriptors of Compounds ==