* Uniformity: Pure substances are made up of only one type of molecule or atom. This means they have a uniform composition throughout.
* Homogeneity: Pure substances are homogeneous mixtures, meaning their properties are the same throughout.
* No Separation: Due to the uniformity and homogeneity, there is no driving force for the different parts of a pure substance to separate and form layers.
Example: Imagine a container of pure water. All the molecules are water (H2O), and they are evenly distributed. You wouldn't see the water separating into layers.
Exceptions:
* Phase Changes: While a pure substance won't separate into different layers due to its composition, it can form layers due to phase changes. For example, if you heat water, it will boil and form water vapor, which is less dense and will float above the liquid water. This is a phase change, not a separation of the substance itself.
* Mixtures: If the substance is not pure, but a mixture, then separation is possible. For example, if you mix sand and water, the sand will settle to the bottom, forming a separate layer. This is because sand and water are different substances.
Key Takeaway: A pure substance will not separate into layers because its composition and properties are uniform throughout.
