Classifying Matter Up to this point, we have only been modeling matter with simple particles The simplest units of substances have been represented by just a single particle waterperfumealuminum air For now, it’s still ok to represent substances this way due to the fact that we currently have no reason not to think this is how they actually are (set aside any prior knowledge of what you think water actually consists of) It is time to start considering what occurs when particles of different substances are mixed  Majority of things in nature are not 100% pure, they are a mixture of substances

Why is it even important to classify matter? Before we try to realize the importance of classifying matter, maybe we should ask ourselves why we classify things in the first place? What are some things you organize in your life by classification? Though it’s possible to live a life (and even understand chemistry) without classification, it only makes it more difficult We classify things to make life easier and understanding things with greater ease By classifying things in science, it becomes much easier to identify patterns and make generalizations that eventually change the way we think about a whole topic Silver, copper, aluminum, and gold conduct electricity All of these are metals Metals conduct electricity By following this classification scheme, we are able to make the generalization that “metals conduct electricity.” Therefore, when people make circuits to provide electricity, the use metal (usually copper) wiring.

So how is matter classified? Pure Substances Mixtures Has a definite set of characteristic properties that depend only on the nature, not the quantity of the substance  Density, melting point, boiling point, specific heat, etc.  For example, water will have a boiling point of C regardless if you boil 10 mL or 10 gallons of water Composed of only one kind of particle  A bar of gold is composed of only gold particles  A glass of clean water is composed of only water particles Exhibits properties that are a combination of the properties of the substances that make it up  Will not have one set boiling point or melting point Composed of more than one kind of particle  A mixture of alcohol and water will contain alcohol particles & water particles

Knowing the properties of a mixture allows us to easily separate it Filtration  Doesn’t work when one substance is dissolved in another Distillation  Can be used to separate a mixture of pure substances based on known boiling points  Can also be used to purify (distillation of alcohol or water)

Mixtures and Compounds mixture of iron and sulfur Why did the iron maintain its magnetism when simply mixed with sulfur?  The properties of a mixture are dictated by the properties of the substances that make it up. Iron was magnetic before the mixture and simply mixing iron and sulfur won’t take away its magnetic properties Why did the iron not maintain its magnetism after it had reacted with sulfur?  The reaction of iron and sulfur produced a pure substance known as iron sulfide. Iron sulfide is a completely different substance than iron so it will not necessarily retain the same properties iron had on its own  We know this is a pure substance because it has all new properties and it is composed of only one type of particle (iron sulfide)

Which are mixtures and which are pure substances? Mixture: B & E Pure Substance: A, C, D, F A mixture of molecules: B Atoms of a pure metal: C Molecules of an element: F A solid compound A A mixture of elements E