Valence electrons and ionic compounds

Valence electrons govern all aspects of ionic compound formation. The number of valence electrons an atom possesses — determined by its group on the periodic table — dictates whether the atom will lose or gain electrons during bonding.

Metals

• Are located on the left side of the periodic table
• Have few, loosely held valence electrons and relatively low ionization energies
• Form cations by losing their valence electrons

Nonmetals

• Are located on the right side of the periodic table
• Have high electron affinities
• Form anions by gaining electrons

Chemical bonds form because the electrostatic attraction between one atom's valence electrons and another atom's nucleus lowers the system's potential energy. Reactivity trends across the periodic table reflect how easily these valence electrons participate in such interactions.

Because elements in the same group share the same number of valence electrons, they exhibit analogous bonding behavior and form compounds with matching formula patterns.

Predictable Charges

• Group 1 metals all form 1+ cations
• Group 2 metals all form 2+ cations
• Group 16 nonmetals all form 2− anions
• Group 17 nonmetals all form 1− anions

These predictable charges allow students to determine the formulas of ionic compounds by combining cations and anions in ratios that produce a net charge of zero. Understanding the connection between periodic table position, valence electron count, and ionic charge is essential for predicting compound formation and explaining reactivity trends on the AP exam.