Chemical Bonding, Electronegativity, Valency, and Oxidation State
Chemical bonds are models of electrostatic attraction that explain stable structures and predictable properties.
Learning goals
- Explain ionic, covalent, metallic, and hydrogen bonding.
- Distinguish exchange and donor-acceptor formation of a covalent bond.
- Use electronegativity to predict bond polarity.
- Separate the ideas of valency, formal ionic charge, and oxidation state.
- Connect bonding and structure to physical properties.
1. Bonding as an energy balance
Atoms form a stable arrangement when attractions between nuclei and electrons outweigh repulsions at a particular distance, lowering the total potential energy. A bond is not a physical stick; it is a model of electron distribution and electrostatic interaction. Bond type is a useful classification, while real bonds form a continuum.
2. Covalent bonding and polarity
A covalent bond contains a shared electron pair. In the exchange mechanism, each atom contributes one electron. In the donor-acceptor mechanism, one atom donates both electrons of the pair into an empty orbital of another particle; after formation, the bond behaves as a covalent bond. Ammonium formation from $NH_3$ and $H^+$ is a standard example.