Structure 2. Models of bonding and structure - The ionic model

Ionic bonding is defined as the electrostatic attraction between oppositely charged ions ($M^{n+}$ and $X^{m-}$).

Ions are formed by the transfer of electrons from a metal atom (which forms a cation: $M \rightarrow M^{n+} + ne^-$) to a non-metal atom (which forms an anion: $X + ne^- \rightarrow X^{n-}$).

The stability of ions is often explained by the octet rule, where atoms gain or lose electrons to achieve a noble gas electron configuration (usually $ns^2 np^6$).

Ionic compounds do not exist as discrete molecules; instead, they form a giant ionic lattice, which is a regular 3D arrangement of alternating positive and negative ions.

The strength of the ionic bond (lattice enthalpy) depends on the charge of the ions and their ionic radii. According to Coulomb's Law, the force of attraction is proportional to the product of charges ($q_1 q_2$) and inversely proportional to the square of the distance between them ($r^2$).

Physical properties of ionic compounds include high melting and boiling points (due to strong electrostatic forces), brittleness (due to repulsion between like-charged ions when layers shift), and solubility in polar solvents like $H_2O$.

Ionic compounds conduct electricity only when molten or in aqueous solution because the ions are free to move (mobile charge carriers); they are insulators in the solid state as ions are fixed in the lattice.