Mixtures and Compounds 2

... Tuesday was the first lab, and it turned out to be deciding whether something was a mixture or a pure substance and, if so, what kind of mixture or what kind of pure substance. She made sense of it in her own way.

First, she basically understood what atoms were.  If you took all the things in the world and broke them down to their most basic building blocks, you would have about 90 elements or basic types of atom.  Scientists have made several more in the laboratory, but everything that exists in nature can be broken down to about 90 types of atom.

If something is entirely made up of one type of atom, then it is a pure substance made up of one type of element.  Solid gold is pretty much just gold, a pure substance made up of one element.  The helium we use in balloons is nearly 100% helium, a pure substance made up of one element.

But atoms join together with other elements to make molecules, and there are also pure substances that are entirely made up of one kind of molecule.  We call this kind of pure substance, "compounds." So distilled water you might buy in a bottle is pretty much just pure water.  Water is a molecule made up of two hydrogens and one oxygen--H2O.  Table salt is basically a lot of one molecule, called "sodium hydroxide."

So a pure substance can either be a lot of one type of atom, an element, or a lot of one kind of molecule, a compound.  Mixtures are collections of more than one type of molecule.  A homogeneous mixture is one where these molecules are mixed evenly, like the air or like tap water from the kitchen faucet.  Tap water not only has water but other minerals like calcium and materials used in purification like chlorine or fluorine.  A heterogeneous mixture is then one where the components aren't mixed evenly, such as your average rock or, yes, snot.