Metal Oxides, Bonding Types and Crystal Structure Theories
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Basic and Acidic Oxides
METAL + O2 → a basic oxide. A basic oxide + H2O → a hydroxide. An oxide can react to form a salt and H2O.
METAL + H2O → typically forms a hydroxide (in some cases, hydrides may form).
NONMETAL + O2 → an acidic oxide (acid anhydride). An acidic oxide + H2O → an acid; acids can form salts + H2O in neutralization reactions.
Basic oxides: definition and examples
Basic oxides: These are binary compounds formed by the union of a metal with oxygen.
Basic oxide formation examples: METAL + O2 → a basic oxide. Examples:
- Na + O2 → Na2O
- Ca + O2 → CaO
- Al + O2 → Al2O3
Formation of hydroxides from oxides
The oxides combine with H2O to form hydroxides:
- Na2O + H2O → 2 NaOH
- CaO + H2O → Ca(OH)2
- Al2O3 + H2O → 2 Al(OH)3 (depending on conditions)
Electronegativity and Bond Classification
Electronegativity: a measure of the ability of an atom or group of atoms to attract electrons. Electronegativity values are used when naming compounds and predicting bond character.
Covalent bonds and multiple bonding
Multiple bonds: Atoms can form different covalent bonds: single, double, or triple bonds. A single bond joins two atoms by a pair of shared electrons.
Covalent bond: This bond takes place between atoms that share electron pairs. Each shared pair is coordinated by both atoms involved.
Hydrogen bonding
Hydrogen bond: A hydrogen bond arises when a hydrogen atom covalently bonded to an electronegative atom is attracted to another electronegative atom. Hydrogen bonds are weaker than covalent bonds but important in molecular structure and properties.
Ionic, polar and nonpolar bonds
Ionic bond: Typically occurs when the difference in electronegativity is about 1.7 or higher. If the difference is lower than ~1.7, the bond is polar covalent; if the difference is 0 or nearly 0, the bond is nonpolar covalent.
Electron Theories and Solid-State Models
Theory of the electron cloud: According to this model, metal atoms delocalize their valence electrons into a shared electron cloud that encompasses the metal atoms.
Band theory
Band Theory: Based on the idea that atomic orbitals in a solid overlap to produce bands of molecular orbitals. These bands determine the electrical and optical properties of materials.
Centered cubic and crystallization
Centered cubic theory: During crystallization, molecules (or ions) of a compound become oriented so they can be stacked in specific directions. This orientation produces a fixed number of planar surfaces and defined corners, characteristics of solid crystals. In organic compounds, crystallization is particularly selective because these crystals grow by addition of molecules of the same type (Krubsack, 1973).