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The History of the Atom

The History of the Atom. Part 1 – The concept of the Atom. A long time ago, in a galaxy country far, far away. There were two philosophers. One was Democritus. Lived in Ancient Greece on the island of Sicily First to use the term atom ( atomos meaning indivisible)

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The History of the Atom

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  1. The History of the Atom Part 1 – The concept of the Atom

  2. A long time ago, in a galaxy country far, far away There were two philosophers

  3. One was Democritus • Lived in Ancient Greece on the island of Sicily • First to use the term atom (atomos meaning indivisible) • Described the atom by mathematics of the day (His peer was Pythagoras) • Atom was described as the smallest part of a material • There were rock atoms, hair atoms, etc.

  4. Democritus’s atom would have looked like this: • Solid and Indestructible • No electrons • No nucleus • No protons • No neutrons • No Experiments to support his ideas

  5. The other was Aristotle • He lived in the heart of Greece (Athens) • Defined matter as composed of hot, cold, wet and dry • These properties related to fire, air, water, and earth • Everything differed by the percentages of each that composed the object

  6. And the winner was: • Aristotle • And set chemistry back about 2000 years • Chemistry didn’t make a come back until the Renaissance

  7. Antoine Lavoisier • Frenchman in the late 1700s • Was working with gases • He discovered that the amount of mass that one started with was equal to the amount of mass that one ended with – Law of conservation of mass. • Also discovered that oxygen caused things to burn • Some call him the Father of Chemistry

  8. Joseph Proust • Another Frenchman a few years after Lavoisier • Proposed Law of Definite Proportions • Roughly stated: a chemical could have only one ratio of atoms within it. • In other words, a compound will always have the same elements in the same ratio • Water has to be H2O and not HO or HO2

  9. John Dalton • Took his own experiments and those of others to write a paper, which later became known as the Modern Atomic Theory • It gave a compilation of the information at the time and allowed other scientist to test his ideas.

  10. Dalton's Atomic Theory • All matter is composed of extremely small particles called atoms, which cannot be subdivided, created, or destroyed. • Atoms of a given element are identical in their physical and chemical properties. • Atoms of different elements differ in their physical and chemical properties. • Atoms of different elements combine in simple, whole-number ratios to form compounds • In chemical reactions, atoms are combined, separated, or rearranged but are never created, destroyed, or changed.

  11. An Analogy for Dalton’s atom An atom is small, spherical and the same throughout. • A small atomic fireball

  12. Dalton also gave us the Law of Multiple Proportions • Elements could combine in different ratios to produce different compounds • For Example, nitrogen and oxygen can form N2O, NO, NO2,N2O3, N2O4, and N2O5.

  13. His ideas weren’t 100% correct, but they gave scientist a good start

  14. Definite and Multiple Proportions – The Math Involved Types of problems that can be asked at this point in time.

  15. Type One – The Easy Type • Table salt is composed of sodium and chlorine. Chlorine comprises 60.66% of the compound, what percentage is sodium? • 39.34% • C, H, and O combine to make C2H6O2. Hydrogen is 9.74% and carbon is 38.70%. What percent is oxygen? • 51.56%

  16. Type 2 – You will need a periodic table for this type • The formula of ethylene glycol is C2H6O2, what percentage by weight do you have of each of the elements? • Step 1 – Calculate the mass of C2H6O2, by adding the mass of each element: • C = 12.01 g x 2 • H = 1.01 g x 6 • O = 16.00 g x 2 = 24.02 g = 6.06 g = 32.00 g 62.08 g

  17. Type 2 – You will need a periodic table for this type • Step 2 – Divide each elemental mass by the mass of the compound • C = 12.01 g x 2 • H = 1.01 g x 6 • O = 16.00 g x 2 • Step 3 – Multiply by 100 • C = 38.69%; H = 9.76%; O = 51.55%  = 24.02 g 62.08 g = 0.3869 = 6.06 g  62.08 g = 0.0976 = 32.00 g  62.08 g = 0.5155 62.08 g

  18. Let’s try this one together What percentage by weight do you have of each of the elements if you have the formula Al2O3?

  19. Now try the rest of the problems with you groups

  20. Answers • 42.9% C and 57.1% O • 77.7% Fe and 22.3% O • 2.7% H and 97.3% Cl • 52.2% C, 13.0 % H, and 34.8% O • 32.4% Na, 22.6% S, and 45.0% O

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