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Elements, compounds, mixtures

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Elements, compounds, mixtures

  1. 1. Elements, Compounds and Mixtures
  2. 2. Elements Elements are basic substances which cannot be further broken down into simpler substances by chemical methods. 115 elements (91 occur naturally, 24 made artificially by scientists) Classified by properties (ie. metal or nonmetal)  Atom - Smallest part of an element that can exist as a stable entity. Represented by symbols. (seeTable 2.4 – you must have these memorized!!!)
  3. 3. Takealookatthechartoftheelementnames andsymbolsthatyouneedtomemorize! Now….OUTLINE these elements in BLUE on your periodic chart!
  4. 4. Molecules - small groups of joined atoms Diatomic Molecules  Molecules that are formed from 2 atoms of a single element.  H2, O2, N2, F2, Cl2, Br2, and I2  Memorize these! Highlight these green on your periodic chart!!! Monatomic Molecules  These are gaseous elements that exist as separate, individual atoms (they tend not to bond with themselves or other elements.)  He, Ne, Ar, Kr, Xe, Rn  Memorize these! Highlight these red on your periodic chart!
  5. 5. Molecules - small groups of joined atoms Molecules can also be formed between different types of atoms: i.e. H20 We call this type of molecule a compound.
  6. 6. Compounds Compounds are pure substances which are formed when 2 or more elements chemically combine. Compounds cannot be separated by physical means – only by chemical reactions. The properties of compounds are very different than their component elements.
  7. 7. Mixtures A mixture contains more than one substance (elements and/or compounds.) Mixtures can be physically separated. Composition is mixed and properties are those of the individual elements.
  8. 8. Element, Compound or Mixture?
  9. 9. Element, Compound or Mixture?
  10. 10. Element, Compound or Mixture?
  11. 11. Element, Compound or Mixture?
  12. 12. Separating Mixtures If a solid substance is soluble it will dissolve when added to a liquid and form a solution. The liquid is called the solvent and the dissolved solid is called the solute. If a solid substance is insoluble it does not dissolve in liquid.
  13. 13. Separating solid/liquid mixtures 1. Filtering 2. Decanting 3. Evaporating 4. Crystallizing 5. Centrifuging 6. Simple Distillation
  14. 14. Filtering Pour mixture into a funnel containing filter paper. The residue (solid) is trapped in the filter paper while the filtrate (liquid) passes through it into a collection container below.
  15. 15. Decanting Slowly pour the mixture into a collection container allowing the filtrate to run along a glass rod to prevent splashing.
  16. 16. Evaporating Evaporation is good if a solid has been dissolved in a solvent and can’t be filtered or decanted. Slowly heat the mixture until the solvent has been completely evaporated and leaves the solid behind.
  17. 17. Crystallizing This is a process that uses the sun to evaporate salt from brine. Brine is a supersaturated solution which contains as much salt as it can dissolve. When the water is evaporated the salt crystallizes.
  18. 18. Centrifuging We use centrifuging when the solid particles are so small they don’t settle to the bottom of a solution, but remained dispersed in suspension. Centrifuging involves spinning the suspension very fast so that the solid is flung to the bottom of the tube. This can be used to separate blood cells from blood plasma.
  19. 19. Simple Distillation
  20. 20. Simple Distillation The solution is heated in the flask until it boils. The steam rises into the Liebig condenser where it condenses back into a liquid and collects in the beaker. The solute is left behind in the flask. This is one way to remove dissolved salt from water.
  21. 21. Separating liquid/liquid mixtures 1. Separating Funnel 2. Fractional Distillation
  22. 22. Separating Funnel A separating funnel is used to separate liquids that are immiscible (liquids that don’t mix). The lower layer can be released by opening the tap.
  23. 23. Fractional Distillation
  24. 24. Fractional Distillation Fractional Distillation is used to separate liquids that are miscible (mixable). It relies on the fact that the miscible liquids have different boiling points. This is one way to separate ethanol and water. Ethanol boils at 78˚C while water boils at 100˚C. As the mixture is heated the vapor is mostly ethanol and some water. The water vapor is condensed out of the vapor and returned to the flask in the fractionating column which has many beads in it.
  25. 25. Fractional Distillation
  26. 26. Separating solid/solid mixtures 1. Chromatography 2. Solvent extraction
  27. 27. Chromatography
  28. 28. Chromatography Chromatography is used to separate two or more solids such as inks or dyes. A spot of ink is placed on chromatography paper. The paper is placed in solvent. As the solvent moves up the paper the dyes are carried with it. They separate because they are dissolved at different rates by the solvent and absorbed to different degrees by the chromatography paper. An Rf value can be calculated. It is the ratio of the distance travelled by the solute (solid) to the distance travelled by the solvent.
  29. 29. Chromatography
  30. 30. Solvent Extraction Solvent extraction can be used to separate two solids. For example, we can use water to dissolve sugar (solid 1) from crushed sugar cane (solid 2). The sugar can then be separated from water by evaporation.
  31. 31. Discuss with a partner: If I gave you a mixture of water, oil, salt, sand and iron chips how would you separate them?