Simpler when it's Sorted

How many of you have to take out the trash?  It used to be so simple; everything just went to one place--the Can.  Nowadays, there are at least 3 cans, one for recyclables, one for yard waste and one for the true trash.  It must be sorted, and the recycling even gets sorted again wherever it goes.  Although it is confusing, it is also extremely helpful and that's why we bother.

Classifying Matter - the chapter we just studied - same thing.  To understand more easily, we sort matter into categories. All of matter can be sorted into two piles; it's either a pure substance or it's a mixture of pure substances.  (Our textbook says something is either a substance or it is a mixture, but I think "substance" sounds too much like "stuff'" so I'm adding the word "pure" to clarify.) Everything must be either pure or a mixture.

Most of the world around us would be put in the mixture pile.  We have to look hard to find anything in nature that is pure.  The air we breathe is a mixture of gases; the water we drink, we have to purify first (and even then it contains impurities). Looking around the room right now I can't see a single thing that isn't mixed.  The salt on my table is pure, but it has been through a process to separate it from its impurities.

Our textbook gives us a few categories for mixtures: solutions, colloids and suspensions.  This is mainly so you can see what a pure substance is NOT.  After this chapter we won't talk about them too much (except solutions).

What we will talk about are pure substances, and we can sort them into two groups. First there are the elements, which are made of a single type of atom, such as hydrogen or helium or carbon or gold.  Not many of these, only about 90 in nature.  But lots and lots of combinations (COMPOUNDS). The compounds have more than one type of atom combined together,  but they are not mixtures because the atoms are bonded to each other strongly and in a definite proportion. For instance, water is a compound; it is composed of two atoms of hydrogen joined like siamese twins to one atom of oxygen.  Water (H2O) is completely different than a mixture of hydrogen and oxygen gases, even though it is made of hydrogen and oxygen. And it is completely different than H2O2, hydrogen peroxide (the stuff in the brown bottle that fizzes when we put it on cuts), because that extra oxygen atom changes A LOT. It changes its identity. It changes its physical and chemical properties. (Sidenote: that bottle of hydrogen peroxide is a mixture of 3% H202 and the rest is simply H20; if you had 30% hydrogen peroxide solution, then you'd see more than fizzing!). H2O2 is not H2O.

The other thing we had to sort through was the pile of physical and chemical properties and  changes.

Each pure substance has its own chemical identity and therefore its own unique set of chemical and physical properties.  A mixture has a jumble of properties.

These are the main ideas from chapter 17: Classifying Matter.  If you think you did poorly on the test, please read the chapter again this weekend.  Chapter 18 focuses on atoms, elements and the periodic table.

Here are two videos to watch: (30 minutes total) Notes in journal

just for fun, a teaspoon made of gallium