1. Substances and Mixtures!

2. Substances:  Matter – everything that has mass and takes up space.  It can be classified by its physical properties.  One way to classify matter is based on its chemical composition.  Matter that has the same composition and properties throughtout is called a substance.  There are two types of substances –elements and compounds.

3. Substances:  Remember that elements are substances made up of only one type of atom.  Different elements can combine to form new substances called compounds.  Compounds are two or more elements that are chemically bonded together.

4. Substances:  Compounds can be broken down only by chemical means in to the elements that combined to make them.  For example, boiling, freezing, stirring or filtering will not separate the hydrogen atoms from the oxygen atoms of water.  However, if electricity is added to water, it can be broken down into hydrogen gas and oxygen gas.

5. Mixtures:  When two or more substances come together but don’t chemically combine or bond to make a new substance, a mixture results.  Unlike compounds, the proportions of the substances in a mixture can be changed without changing the identity of the mixture.  For example, if you put some sand into a bucket of water, the sand doesn’t chemically combine with the sand and water.

6. Mixtures:  Physical properties can be used to separate mixtures into simpler substances.  The solid sand can be filtered from the liquid water using a sieve.

7. Homogeneous Mixtures:  Homogeneous means ¨the same throughout.¨  Homogeneous mixtures contain more than one substance evenly mixed but not chemically bonded together.  You can’t see the different parts in a homogeneous mixture no matter how closely you look.

8. Homogeneous Mixtures:  Homogeneous mixtures can be solid, liquid, or gas.  The brass in a trumpet is a solid mixture of zinc and copper –two elements.  Sugar water is a homogeneous liquid mixture of water and sugar –both compounds.  Air is a homogeneous mixture of elements: nitrogen, oxygen, argon, neon, and helium –and two compounds: carbon dioxide and water.  Homogeneous mixture is also known as a solution.

9. What is the difference between a substance and a homogeneous mixture?  The difference between a homogeneous mixture and a pure substance is that a pure substance has a fixed composition and cannot be separated because it is chemically bonded and a homogeneous mixture can be separated.

10. Heterogeneous Mixtures:  A hererogeneous mixture is one of two or more substances that are not mixed evenly.  You can see the different parts of a heterogeneous mixture, such as a mixture of sand and water.  A pizza is a heterogeneous mixture.  Other examples include salad, a bookshelf full of books, or a toolbox full of nuts, bolts, screws, nails, and tools (etc.).

11. Questions…  What is the difference between a homogeneous and a heterogeneous mixture?  How are substances different from homogeneous mixtures?

12. The end!