Ionic and covalent bonding
Atoms bond through valence electrons. A large attraction difference favors electron transfer and ions; a smaller difference favors shared electron pairs.
Learning goals
- use valence electrons and Lewis dots;
- distinguish transfer from sharing;
- explain cations, anions, lattices and molecules;
- use electronegativity qualitatively to predict bond type and polarity.
1. Valence electrons and stability
Valence electrons occupy the outer shell and participate most directly in bonding. Many main-group atoms form bonds that give them a stable outer arrangement: two electrons for the first shell or often eight for later main shells. This duet/octet guide is useful for simple grade-8 compounds, but it is a model rather than a universal law.
2. Ionic bonding: transfer and attraction
- A metal atom loses one or more valence electrons and becomes a positive cation.
- A nonmetal atom gains those electrons and becomes a negative anion.
- Opposite charges attract in every direction, building an extended ionic lattice.
For sodium chloride, Na loses one electron: $Na\rightarrow Na^+ + e^-$. Chlorine gains it: $Cl+e^-\rightarrow Cl^-$. The compound is electrically neutral because total positive and negative charge balance.
Structure matters: solid sodium chloride is an ionic lattice, not a collection of separate NaCl molecules.