What kind of structure does your substance have?
You can work out the chemical structure of a substance by looking at its physical properties.
If it is a gas, liquid or a soft solid with a low melting point, then it is a simple covalent substance.
If it is a solid with a high melting point then it has a giant structure, and is either an ionic, covalent or metallic compound.
If the substance dissolves in water (without a reaction), it is probably ionic.
If it’s a solid that conducts electricity, it will be a metal or graphite (a substance with a giant covalent structure).
If it’s shiny and malleable, it will be a metal.
If it’s a brittle material, it has a giant covalent structure.