Classification of Matter: The Matter Family Tree
What’s in a name?
Shakesphere wrote, “That which we call a rose by any other name would smell as sweet,” in a sonnet for Juliet, who argued that names are not important, but rather what something is. Well, dear Juliet, not in chemistry.
Differences in terms we use interchangeably in everyday language, for example molecule versus compound, may seem trivial, but they are not. They mean different things!
Let’s sort it out…
Matter is composed of 1) Pure Substances and 2) Mixtures as the flow chart below illustrates. Those categories are then further divided into specific types of matter (molecules, atoms, etc)
Below are definitions that will help you differentiate between components of matter found in the flow chart. Pure Substances: Cannot be purified further, just into either component elements
Elements: a substance that cannot be broken down into a similar substance by chemical means. These can be found on the periodic table.
Ex. aluminum (Al), sodium, chlorine, (Cl), etc.
Atom: a unit of an element; the smallest particle of an element that retains the characteristics of that element. Think of this as the element’s DNA—it’s unique identity.
One atom of Al
When ATOMS of two or more ELEMENTS combine, they form a compound…
Compound: a combination of two or more elements chemical combined in a fixed ratio Example: sodium chloride, NaCl
Note the difference between sodium as an element alone (left) and combined with chlorine to form a NaCl as a compound (right).
Molecule: a unit of a compound
Mixtures: two or more pure substances that are physically—not chemically—combined, either evenly or unevenly. Mixtures can be separated into their components by physical means (evaporation, decanting, etc).
Homogenous Mixture: an uniform blend of two or more substances such that all phases are combined evenly; a solution or uniform composition throughout.
Example: salt water solution, coffee with sugar dissolved
Heterogeneous Mixture: an un-uniform or varying composition of two or more substances such that all phases are NOT combined evenly and all phases are visible.
Example: oil and water, salad dressing, iron fillings in sand, fat and proteins in milk, slabs of granite (below)