Chapter 7 Ionic and Metallic Bonding Ch. 7.1 Ions

Valence Electrons Elements within each group of the periodic table have the same number of valence electrons, so they behave similarly. Valence electrons—the electrons in the highest occupied energy level of an element’s atoms. For a representative element, the group number is also the number of valence electrons. Exception: helium—2 valence electrons.

Valence electrons are usually the only electrons used in chemical bonds. Only valence electrons are shown in electron dot structures, in which valence electrons are shown as dots.

The Octet Rule An octet (8 electrons) in the outermost energy level is stable. In forming compounds, atoms tend to achieve the electron configuration of a noble gas. Atoms of metallic compounds tend to lose their valence electrons, leaving a stable octet in the next-lowest energy level. Atoms of some nonmetallic elements tend to gain electrons or to share electrons with another nonmetallic element in order to achieve a complete octet.

Formation of Cations An atom’s loss of valence electrons produces a cation, or a positively charged ion. Some cations formed by the transition metals are exceptions to the octet rule. Name of the cation is the same as the name of the atom from which it formed.

Formation of Anions Anion—atom or group of atoms with a negative charge. The gain of negatively charged electrons by a neutral atom produces an anion (a negative ion). The name of an anion typically ends in –ide. (Chlorine…chloride; Oxygen…oxide). Halides—formed when chlorine and other halogens gain electrons.