Chemical bonds.  Chemical bonds are the attractive forces that hold atoms together in more complex units. Chemical bonds result from the transfer of valence electrons between atoms (ionic bond) or from the sharing of electrons between atoms (covalent bond).

Valence electrons.   Valence electrons, for representative elements, are the electrons in the outermost electron shell, which is the shell with the highest shell number. These electrons are particularly important in determining the bonding characteristics of a given atom.

Octet rule.   In compound formation, atoms of representative elements lose, gain, or share electrons in such a way that their electron configurations become identical to those of the noble gas nearest them in the periodic table.

Ionic compounds.   Ionic compounds usually involve a metal atom and a nonmetal atom. Metal atoms lose one or more electrons, producing positive ions. Nonmetal atoms acquire the electrons lost by the metal atoms, producing negative ions. The oppositely charged ions attract one another, creating ionic bonds.

Charge magnitude for ions.   Metal atoms containing one, two, or three valence electrons tend to lose such electrons, producing ions of _1, _2, and _3 charge, respectively. Nonmetal atoms containing five, six, or seven valence electrons tend to gain electrons, producing ions of _3, _2, and _1 charge, respectively.

Formulas for ionic compounds.   The ratio in which positive and negative ions combine is the ratio that causes the total amount of positive and negative charges to add up to zero.

Structure of ionic compounds.  Ionic solids consist of positive and negative ions arranged in such a way that each ion is surrounded by ions of the opposite charge.

Binary ionic compound nomenclature.   Binary ionic compounds are named by giving the full name of the metallic element first, followed by a separate word containing the stem of the nonmetallic element name and the suffix -ide. A Roman numeral specifying ionic charge is appended to the name of the metallic element if it is a metal that exhibits variable ionic charge.

Molecular compounds.   Molecular compounds usually involve two or more nonmetals. The covalent bonds within molecular compounds involve electron sharing between atoms. The covalent bond results from the common attraction of the two nuclei for the shared electrons.

Bonding and nonbonding electron pairs.   Bonding electrons are pairs of valence electrons that are shared between atoms in a covalent bond. Nonbonding electrons are pairs of valence electrons about an atom that are not involved in electron sharing.

Types of covalent bonds.  One shared pair of electrons constitutes a single covalent bond. Two or three pairs of electrons may be shared between atoms to give double and triple covalent bonds.

Molecular geometry.   Molecular geometry describes the way atoms in a molecule are arranged in space relative to one another. VSEPR theory is a set of procedures used to predict molecular geometry from a compound's Lewis structure. VSEPR theory is based on the concept that valence shell electron pairs about an atom (bonding and nonbonding) orient themselves as far away from one another as possible (to minimize repulsions).

Electronegativity.   Electronegativity is a measure of the relative attraction that an atom has for the shared electrons in a bond. Electronegativity values are useful in predicting the type of bond that forms (ionic or covalent).

Bond polarity.   When atoms of like electronegativity participate in a bond, the bonding electrons are equally shared and the bond is nonpolar. When atoms of differing electronegativity participate in a bond, the bonding electrons are unequally shared and the bond is polar. In a polar bond, the more electronegative atom dominates the sharing process. The greater the electronegativity difference between two bonded atoms, the greater the polarity of the bond.

Molecular polarity.   Molecules as a whole can have polarity. If individual bond polarities do not cancel because of the symmetrical nature of a molecule, then the molecule as a whole is polar.

Binary molecular compound nomenclature.   Along with the names of the elements present, names for binary molecular compounds usually contain Greek numerical prefixes that give the number of each type of atom present per molecule.

Polyatomic ions.   A polyatomic ion is a group of covalently bonded atoms that has acquired a charge through the loss or gain of electrons. Polyatomic ions are very stable entities that generally maintain their identity during chemical reactions.