L3: Classification of Matter

Lesson 3: Classification of Matter (Sophomore Level Chemistry)

Intro:  Matter is Scientific Word for Stuff.  Review:  Matter is anything that has mass and takes up space (volume).  Examples of matter:  sand, clothing, air, books, etc. 

Why classify:  Helps keep things organized.  Example of a clothing store:  imagine walking into the store and everything is randomly set throughout.  How would you find what you want?  Classification allows us to sort and find what we are looking for.  In chemistry, similarly classified matter often has similar properties so we can predict properties of one sample based on what we know about others like it.

What defines all matter:  Something that every substance, mixture, thing has in common: atoms.  Atoms are joined by bonds to create all the matter that we see around us. 

Whole Class Activity:  Filling Out Concept Map

I will hand out blank concept maps and as a class we will go through and complete them.  Spaces will be filling with: Matter, Pure Substances, Mixtures, Elements, Compounds, Heterogeneous Mixtures, Homogeneous Mixtures, and examples of each with supporting lines filled in with connections.  A possible example of what the class should come up with is provided.  As we go through this, I will fill out along on the overhead.  At each step of the concept map, I will be asking different questions to guide students to possible answers.

We have placed matter in the center.  How can we further classify it?  What makes different things different?  Piece of paper different from the desk?  Seem to be made of different things.  If different matter is made of different things, is there any matter out there that is made of just one thing?  Pure substance (put it in the concept map).  What defines a pure substance?  If we do things (cut, burn, freeze, smash) different samples of a pure substance, will it act differently? No.  So we define pure substance as something that has certain properties that can identify it.  Can we further break down a pure substance?  Example: water.  Water has certain characteristics that define it every time, but water is made up of hydrogen and oxygen.  So there must be further distinction.  What are hydrogen and oxygen:  Elements (put in the mad).  Elements contain only one type of atom.  They are what make up the periodic table.  Each element has certain physical and chemical properties that make it unique from all others.  Returning to our example of water, elements can be combined into Compounds.  While elements cannot, compounds can be chemically broken down, but it requires a lot of energy.  The elements that make up a compound always are chemically joined and always in the same ratio.  Water is always always always H2O.  If the ratio is off it is no longer water.  What happens if we combine two pure substances, or if we MIX them Get a Mixture.  Examples of mixtures:  foods, air…. Air is not a pure substance like water because the ratio of its components is not always equal.  Are there different kinds of mixtures?  Think about what happens when you mix salt or sugar and water and what happens when you mix oil and water?  Some mixtures mix cleanly throughout, some do not.  Homogenous mixture.  Go over that homogeneous means the same throughout so a homogeneous mixture the pure substances that make up the mixture are distributed evenly throughout.  A tablespoon of sugar in a glass of water will make a homogeneous mixture.  So then what is oil and water or sand in water?  Heterogeneous mixture.  Heterogeneous means different so a heterogeneous mixture is different throughout, or doesn’t mix well.  

A common misconception is to think that compounds and mixtures are the same thing.  What makes them different?  Compounds are chemically joined.  Mixtures are mixed, but not chemically joined. 

So to summarize all that, here are the guiding questions to fill the concept map:

  • What makes up all things?
  • What makes up different kinds of matter?
  • Is there anything that is just one thing?
  • Further break down of pure substance, is water just one thing?
  • What happens when we combine elements?
  • What happens when we mix pure substances?
  • Do some substances “mix” better than others?
  • Homogeneous/Heterogeneous
  • What makes compounds and mixtures different?

Group Activity:  Make your own elements, compounds, HM Mixtures, and HG Mixtures

Have the students form into four groups.  Distribute four, clear plastic cups to each.  Tell them they are responsible for representing all of the classifications of matter in their cups with the M&Ms provided.  Each group will also be responsible for showing one of their cups to the class and explaining why it is what they say it is.  Four containers will be provided to the whole class that each contain one color of M&M. 

Element should have all one color of M&Ms. 

Compound should have at least two different colored M&Ms in a definite ratio.

HG Mixture, at least two different colors but not mixed well.  For example should have a layer of one color and a layer of another color. 

HM Mixture:  Hardest to represent, give effort points.  A group with great understanding will first make two separate compound and/or element cups and then mix them and shake them up so they are assorted evenly throughout each other.

Time management point:  if time is running thin or students are getting off task, tell them they only get to eat their mixtures if they finish in time.

Homework: read pages 21-28.  Section Review Questions 1-8.

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Published on December 4, 2008 at 5:25 am  Leave a Comment  

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