Nonmetals, Periodic Patterns, and Allotropy
Nonmetal behavior follows electron structure, while allotropy shows how different arrangements of one element produce different properties.
Learning goals
- Locate nonmetals and explain broad periodic patterns.
- Relate valence electrons to bonding and oxidation states.
- Compare oxidizing and reducing behavior.
- Define allotropy and connect structure with properties.
- Compare oxygen, carbon, sulfur, and phosphorus allotropes.
1. Periodic position and properties
Most nonmetals occupy the upper-right region of the periodic table, with hydrogen as a separate nonmetal at the upper left. Across a period, atomic radius generally decreases while electronegativity and first ionization energy generally increase. Down a group, radius increases and electronegativity often decreases.
Many nonmetals form covalent molecules or networks. Their simple substances range from gases to brittle solids; graphite is an important conducting exception. Physical state depends on particle size, molecular shape, intermolecular forces, and network structure.
2. Bonding and reactivity
Nonmetal atoms often gain electrons in ionic reactions or share electrons in covalent bonds. Typical negative oxidation states reflect the electrons needed for a noble-gas-like valence shell: halogens often −1, oxygen usually −2, and nitrogen can be −3. Many nonmetals also show positive oxidation states when bonded to more electronegative elements.