Why three solids need three different explanations — Physical Science: Chemistry

A salt crystal, copper wire and a molecular solid can all look continuous at human scale while having different microscopic arrangements. An ionic formula gives a neutral ratio in an extended lattice. Metallic bonding can support delocalized electronic carriers. A molecular substance has internal covalent bonds and between-molecule interactions; an extended covalent network requires yet another structural account.

Conductivity is a useful test only when phase and carriers are specified. Ions fixed in an ordinary salt lattice cannot move like dissolved ions, while copper can carry electronic current in the solid. One property does not uniquely identify a substance: defects, composition, temperature and structure affect comparisons. Avoid treating ionic, covalent or metallic as complete property lists.

Lewis structures track valence electrons, VSEPR helps organize common geometry, and polarity requires the spatial combination of charge-distribution contributions. Linear CO₂ can have polar bonds whose dipoles cancel; bent water does not have that same symmetry. A flat line drawing, a formal charge and a partial charge are different models, each useful for its own question.