In chemistry, physical properties are divided into two main categories: intensive and extensive. An intensive property is intrinsic to the nature of the material itself. It is not affected by how much of the substance you have in your sample.
Whether you are analyzing a tiny crystal of a mineral or a massive boulder of the exact same material, their intensive properties will be identical.
Some of the most common and easily observable intensive properties are color, odor, and luster. More measurable intensive properties include boiling point, melting point, and temperature. For instance, a small cup of boiling water and a large pot of boiling water will both have a temperature of exactly 100 degrees Celsius under standard atmospheric pressure, proving that boiling point is independent of sample size.
Density is another critical intensive property, defined as the mass of a substance divided by its volume. Although mass and volume are both extensive properties that change depending on the sample size, their ratio remains perfectly constant for any given uniform substance. This makes density a highly reliable metric for identifying materials; pure gold will always have a density of 19.3 grams per cubic centimeter, regardless of the nugget’s size.
Because intensive properties are unique signatures of specific materials, they are the primary tools used in analytical chemistry to identify unknown compounds. If a scientist needs to determine whether a clear liquid is water or alcohol, they cannot rely on extensive properties like mass or volume, as these can easily overlap.
Instead, they will measure intensive properties like density, boiling point, or refractive index to make a positive identification.