Elements, Compounds and Mixtures

1. Elements, Compounds and Mixtures

2. Elements • consists of only one kind of atom, • cannot be broken down into a simpler type of matter by either physical or chemical means, and • can exist as either atoms (e.g. argon, Ar) or molecules (e.g., nitrogen, N2).

3. Compounds • consists of atoms of two or more different elements bound together, • can be broken down into a simpler type of matter (elements) by chemical means (but not by physical means), • has properties that are different from its component elements, and • always contains the same ratio of its component atoms. (can write a formula for compounds)

4. Mixtures • consists of two or more different elements and/or compounds physically intermingled, • can be separated into its components by physical means, • often retains many of the properties of its components, and • different components are not bonded. (cannot write a chemical formula for mixtures)

5. Activity Time • You will be handed an envelope with some cards. Each card has a term on it. Organize the cards to form a diagram or picture that links each of the terms. • You have a few minutes to come up with your idea.

6. Does yours look similar to this?

7. What is a pure substance? • A pure substance has a constant, defined composition and cannot be separated into simpler substances by physical means. There are two types of pure substances, elements and compounds. • Elements are pure substances that are made of only one type of atom. The periodic table is a table containing all elements. • Compounds are pure substances that are made of more than one type of atom, and can be decomposed or broken down into its elements by chemical means.

8. What do I mean by “Physical means”? • Chromatography - To separate different colored dyes. The dyes travel up the chromatography paper at different distances before they cannot remain in solution. The more soluble dyes move further up than the less soluble ones, hence separating from each other. • Distillation - to separate and collect a liquid from a solution of a soluble solid. The solution is heated in a flask until the liquid boils. The vapor produced passes into the condenser where it is cooled and condenses to a liquid. The pure liquid (distillate) is collected in a beaker. • Evaporation - This method is suitable to separate a soluble solid from a liquid. If the solution is heated, the liquid evaporates leaving the solid behind. • Fractional Distillation - This is a special type of distillation used to separate a mixture of liquids. Different liquids boil at different temperatures. When heated, they boil off and condense at different times. • Filtration - To separate an insoluble solid from a liquid. The solid remains in the filter paper and the liquid goes through the paper into the beaker. • Decant - pouring a liquid off a solid • Magnets - if one compound of a mixture is magnetic you could use a magnet to remove it. • Centrifuge - this separates mixtures really well if you cant filter or decant • AND THERE ARE MORE…This is just a few to get you started…

9. So, what are “chemical means” of separation? • Chemical methods uses energy and a new substance is formed in the process • To chemically separate a substance, a chemical change is required • The breaking of bonds between atoms occurs. Collection of the resulting products can be difficult.

10. What kinds of mixtures exist? • A mixture is composed of more than one element and / or compound. • Different mixtures of the same substances can have different compositions (i.e., a mixture of water and sodium chloride may be 80% water and 20% sodium chloride, or 20% water and 80% sodium chloride.) • There are two types of mixtures, homogeneous and heterogeneous.

11. Homogeneous mixture • A homogeneous mixture has the same composition of elements and / or compounds throughout. • If you observed a homogeneous mixture under a microscope, you would see that the particles of various components are evenly distributed. • A homogeneous mixture is also called a solution.

12. Heterogeneous mixture • A heterogeneous mixture has different regions or areas with different compositions and properties. • The substances in a heterogeneous mixtures are not evenly distributed. • We say that we can see “distinct phases” of matter in a heterogeneous mixture (i.e. the ice cubes, the soda and the straw would be three separate phases in a glass of cold soda) • In contrast a suspension is a heterogeneous mixture of larger particles. These particles are visible and will settle out on standing. Examples of suspensions are: fine sand or silt in water or tomato juice

13. Here is how to “picture” the particles in each…

14. What do each represent? Mixture? *Homogeneous? *Heterogeneous? Element? Compound?

15. Practice what you know • This link is to an interactive quiz • Another link to an online quiz • One more (only 5 questions!) • A matching on-line game