The odour of a substance is related to the shape and atomic composition of the molecules producing the odour. For the substance to reach the nerve sensors in the nose, the material must be volatile. This means it should be able to evaporate and appear in gaseous form.
Sugar and salt have powerful tastes, but both are odourless as they do not evaporate easily. Perfumes contain compounds that evaporates easily .
The nasal sensors have receptor sites that accommodate the shape and chemistry of odour producing molecules. When the vapours reach nasal sensors, an electrical signal is sent to the brain. Different molecular shapes and compositions causes responses in different sensors. Our odour sensors are very sensitive. Certain animals have much better smell sensors than humans. Dogs fall under this category and are often trained to identify objects through smelling.