2. Compounds and Elements Breaking it Down

3. Compounds and Elements  Compounds are pure substances  They are made up of two or more elements chemically bound together.  So what are elements??

4. The Elements - a brief history  For thousands of years people wondered why matter behaved the way it did. “What is everything made of?” “Why does water freeze?” “What am I made of?”

5. The Elements - a brief history  Philosophers spent a lot of time thinking and talking about matter but very little time doing anything with it. I don’t want to get my hands dirty!

6. The Elements - a brief history  For centuries scientists and philosophers believed that all matter was made up of  Earth  Air  Fire  Water

7. Earth Wind and Fire When they look like this…. Not these guys ! I looked like this…. Ahhh….the ‘70s

8. The Elements - a brief history  This view of all matter being made up of only four elements lasted until the 17th century in Europe,

9. Alchemists  While philosophers were thinking about matter, Alchemists were doing something about it.  Believed that one element could be changed into another.  Part Chemist, Part Magician Lead Gold

11. Alchemists  Alchemists did all sorts of hands-on chemistry.  They did many experiments and discovered many things.  They were very secretive and developed a secret code to keep track of their experiments.

12. Sir Francis Bacon 1561 - 1626 In the 17th century Francis Bacon wrote a book that changed the way people thought about science. Bacon asked people to let go of the old way of looking at science He developed the scientific method. Convinced people that science should be based on experimental observation, not just thought.

13. Robert Boyle 1627-1691  First scientist to express public skepticism of the “four elements” view of matter.  Called elements “unmingled bodies”.  Recognized that elements could be combined to form compounds.

14. Breaking it down…  In the 17th century scientists got very excited about breaking matter apart until it couldn’t be broken apart anymore.  These elemental parts are called elements.  They heated, burned, cooled and mixed everything they could get their hands on to see how things could be broken down.

15. The Mad Scientist Was Born

16. Antoine Lavoiser 1743 - 1794  Lavoiser was a pioneer in this field.  He identified 23 new elements by breaking things down into the smallest parts.  Realized that measuring the mass of all parts of a chemical reaction was essential to making inferences about what was happening in chemical reactions.

17. Volta!!  In the 19th century a new investigative tool was invented - the Voltage Pile.  Invented by Allesandro Volta  Essentially - a battery.

18. Voltage Pile  The voltage pile was much like a battery.  Delivered a reliable supply of electric current.  What did scientists do first?

19. Stick It Up Their Nose?

20. Eat it?

21. Nope! They did something way cooler.  They immediately began passing current through water… and what do you think happened?

22. Making Gas….  They found that a) hydrogen and oxygen gases were produced. b) the water level fell slightly Hmmm………..

23. Inferring….  They inferred that some of the water had been decomposed into hydrogen and oxygen.

24. So if that works….  Humphry Davy (1778-1829) wanted to see what else could be decomposed using electricity.

25. Using Current…  Davy discovered…  Potassium  Sodium  Magnesium  Calcium  Barium  Strontium Davy found that he had to start with a liquid mineral or a solution of a mineral. His assistant, Mike Faraday called this process electrolysis.

26. Not this kind of electrolysis

27. This kind…

28. Law of Definite Porportions  Compounds are pure substances that contain two or more elements combined together in fixed or definite amounts.  So… if you have 300 units of water you will have 200 units of Hydrogen and 100 units of Oxygen.  Because of the difference in weight… Water = 11% Hydrogen + 89% oxygen

29. Law of Definite Porportions  Hydrogen peroxide contains H and O but in different proportions… 6 % Hydrogen + 94% Oxygen These proportions always hold true.

30. Properties of Compounds  Pure substances have constant composition  They also tend to have constant properties - they tend to always behave the same way.  We can use these constant properties to identify the element…  How might you do this?

31. One more thing… Law of Conservation of Mass  In a chemical change, the total mass of the new substance is always the same as the total mass of the original substances.  What goes in gotta come out