A material's formula is only the beginning. Its melting point, conductivity, solubility, hardness and flexibility depend on whether particles form molecules, a lattice of ions, a metal lattice or a giant covalent network. Learning to infer structure from evidence is one of chemistry's most transferable skills.

Start by asking what particles are present and what holds them together. Simple molecular substances contain individual molecules; ionic substances contain ions; metals contain positive ions and delocalised electrons; giant covalent materials contain atoms joined by a continuous covalent network.

The same element can form different structures, so composition alone is not enough. Carbon as diamond, graphite and graphene illustrates why a structural model, not a formula, is needed to predict properties.

Macroscopic properties follow from the particles present and the interactions holding them together. A giant covalent network has many strong covalent bonds throughout its structure, whereas a simple molecular solid melts by overcoming intermolecular forces without breaking every covalent bond inside molecules. Electrical conduction requires mobile charged particles or electrons. Compare materials by explicitly naming the particles, the interaction overcome on melting, and any mobile charge carrier.

Melting or boiling a simple molecular substance separates molecules but does not normally break their covalent bonds. Because intermolecular forces are much weaker than covalent bonds, these substances commonly have low melting and boiling temperatures and may be gases or liquids at room temperature.

They do not conduct electricity unless ions are produced in solution, because their molecules have no mobile charged particles. Solubility depends on the balance of attractions: substances capable of forming similar interactions to a solvent tend to dissolve more readily.

Giant ionic lattices have high melting temperatures and conduct only when ions are mobile in a melt or solution. Giant metallic structures conduct as solids because delocalised electrons move through the lattice and are often malleable because layers can slide while metallic attraction remains.

Giant covalent structures such as diamond and silicon(IV) oxide have strong covalent bonds throughout, so they are hard and have very high melting temperatures. They normally do not conduct because all electrons are localised in bonds, although graphite and graphene are key exceptions with delocalised electrons.

In diamond, each carbon forms four covalent bonds in a three-dimensional tetrahedral network. It is hard, has a high melting temperature and does not conduct because all four outer electrons are used in localised bonds. Its hardness makes it useful in cutting and abrasion.

In graphite, each carbon forms three covalent bonds in planar layers; the remaining electron is delocalised. The layers are held together by weak forces and can slide, so graphite is soft and can act as a lubricant, while delocalised electrons allow electrical conduction along the layers. Graphene is one atom thick and combines strength with high conductivity.

A single property can mislead. High melting point may indicate ionic, metallic or giant covalent structure; electrical conduction in a solid suggests a metal or graphite, while conduction only after dissolving suggests mobile ions. Combine observations to make a defensible classification.

Material selection is an applied structure question. A cable needs low resistance and ductility, a cutting tool needs hardness, and a heat-resistant crucible needs a high melting temperature and chemical stability. Explain the chosen property through the material's particles and bonding.

A solid should be classified from several properties together. A low melting temperature and poor electrical conductivity suggest simple molecular structure, whereas a high melting temperature and conduction only when molten suggest a giant ionic lattice. A giant covalent solid usually has very strong directional bonds and a high melting temperature; graphite is the important exception because each carbon has one delocalised electron and weak forces between its layers.

Solubility also needs a particle-level explanation. Ionic compounds may dissolve in polar water when ion–dipole attractions compensate for lattice separation. Molecular substances dissolve best when the new solute–solvent attractions are comparable with the attractions already present. A substance being polar does not guarantee that it dissolves in every polar solvent; shape and hydrogen-bonding sites also matter.

A structured practical comparison combines electrical conductivity, solubility, hardness and supplied melting data. It develops the habit of making a conclusion from converging evidence rather than one familiar-looking observation.

Work from an evidence pattern to a model, then back to each observation.