Science is a Process, not an Object.

Honors Chemistry

My hosted Screencasts.

Blog Entries

Stacks Image 240

Classification of Matter

What is Matter?

This is only the first of many times we will address the question "What is matter?," with increasing detail each time. From the standpoint of simply organizing what we can see and measure, we organize matter essentially by how hard it is to separate things into other things.
Terms in italics are sort of vocabulary words you should know.

Mixtures, compounds and elements.

Mixtures contain components whose properties can still be detected in the mixture. So, in lemonade for example, you can taste the presence of the lemons and the sugar, maybe even see the lemon pulp, and you know there is water. If you dried out the lemonade, you would have the sugar, and some of the components of the lemon juice left behind. This is another characteristic of mixtures: they can be separated by physical means. Physical means are actions that do not alter the characteristics of the matter being separated. The lemon juice still is tart. The sugar still is sweet, etc. Really, the two ideas: “mixture” and “physical means;” are connected. See if you can describe for one of your friends how these two ideas are linked.
Mixtures can be obviously mixtures...
heterogeneous which you can readily recognize the different components are there. They also can be homogeneous, which means they seem uniform in their composition. This distinction, which amounts to how “chunky” something seems, is a little arbitrary, depending on how closely you look. Is “air” homogeneous or heterogeneous? Well, if you look at the air in the room, it looks pretty homogeneous. If you look at the air over Los Angeles from a hillside, on the other hand--kind of chunky. So, this distinction is not as clear as the others.

Compounds and Elements are both pure substances. This just means that they are not mixtures. Instead they maintain their own properties as you separate them from other pure substances. Sugar is a compound. Whether pure or in a mixture, it has the property of being sweet, for example. You cannot separate them into simpler components by physical means. They differ from each other in that compounds can be separated into simpler components, namely elements, through chemical means. Elements cannot be separated into simpler components even by chemical means. So, elements cannot be separated by chemical or physical means...that’s simple enough. How can you discern the physical breaking of a mixture into simpler components from the chemical breaking of compounds into elements? Let’s think about the lemonade example: when you collect the sugar and the water and the lemon extracts, you can easily tell what each of them contributes to the whole. The water contributes the liquid nature of the lemonade (it’s the ‘solvent’); the sugar contributes the sweetness and the lemon contributes tartness etc. On the other hand, you could take the sugar and heat it on the stove and obtain water vapor (steam) and a black substance in the pan (carbon). There is nothing about either of these components that contributes obviously to the properties of sugar. A mixture has properties that are essentially the sum of the properties of its components, whereas a compound has properties that are quite different from is components. There are some obvious examples that are always chemical changes, such as burning. But, if you are not sure on a particular case, just ask if the change involves changing the properties of the matter entirely, or simply separating components that maintain the properties they had in the mixture. If it is the latter, think “physical change.” If the former, think “chemical change."


States of matter

We will be dealing with 3 states of matter.
Solid, Liquid and Gas (the are others, such as “plasma” and “Bose-Einstein Condensate,” but we won’t deal with those at all--oh, perhaps I won’t be able to resist telling you about them...but I won’t test you on them). Most of you could come up with ways to describe the differences. You know, for example, that a solid has both defined volume and shape, a liquid has defined volume but can adopt the shape of its container and finally that gas adopts both the shape and volume of its container. During the next experiment, you will obtain direct evidence at the different forms of matter are really different forms of the same stuff. For example, you will see that the same matter can be solid (as in ice), liquid (as in water), or gaseous (as in water vapor). How could the same stuff I adopt forms with such very different properties? The solid form of matter may seem the most intuitive state. It makes perfect sense that if I push against something made of matter, I shouldn't be able to move through it. It works fine when I consider ice. Water is trickier though. It clearly has mass, it clearly occupies space; but I can move through it. As I push against it it will move out of my way provided there is space for it to move into. Gaseous forms of matter seem even less like "matter." I've good evidence that they are matter: if I blow against my arm I feel something hitting it; water vapor can be condensed back into a more familiar form of matter (liquid); if I fill a balloon with air, clearly there is some substance inside it. But the behavior of this form of matter seems strange. Not only does it move out of my way as I push against it if there is space for it to move to (as the liquid form does), but even if there isn't any space into which it can move, I can still move through it, compressing it into a smaller space. Now that doesn't seem like "matter" at all. What would allow the same stuff to adopt these three very different forms? But, as a chemist, it is worth noting that these properties that we recognize derive directly from the properties of the bonds (or lack thereof) between the particles. Matter is made up of small particles. I do plan to give you very strong evidence to support that. For now, hold off for say, a week or so. The bonds of a solid are fixed both in the distance between the particles and the position of the particles. Particles can vibrate, and in fact can be moving rather quickly (depending of the temperature). But the stay in the same relative position to each other and the distances are fixed within a narrow range. The bonds of a liquid are also fixed in terms of the relative distance between the particles, just like those of a solid. Because the distance between the particles is small and fixed, both solids and liquids are called "condensed" states of matter. But, liquids differ from solids in that the position of the particles can change relatively freely. The particles can flow freely over each other, and so this state of matter is called a fluid. Gases are like liquids in that the particles can flow over each other (so a gas is a fluid like a liquid). But gases differ from the condensed forms of matter (solid and liquid) in that the distances between the particles are varied and large (this accounts for the ability of a gas to fill all the space available to it. Can you see how the properties we attribute to the three states of matter derive from the nature of the interaction between the particles?
States of matter

Made with Padlet
MathJax Font RapidWeaver Icon

Made in RapidWeaver