A Quick History of Chemistry

1. A Quick History of Chemistry With thanks to Isaac Asimov

2. The Greeks • Aristotle suggested that everything was composed of 4 elements: • Water, Air, Earth and Fire • He later added a 5th element which he called “aether” which the stars and the heavens were made from. • Would you like to see 3 of those original Greek Elements?

3. Earth Wind and Fire(http://www.earthwindandfire.com/bio.html) Yes, I’m “old school.” But I love these guys. And, I even saw them in concert once, back in the 80’s. OK, back to chemistry history…on the NEXT slide…

4. Democritus—400 BC(http://www.gap-system.org/~history/Mathematicians/Democritus.html) Democritus was the first to suggest that matter was composed of atoms, which he called “atamos” meaning “indivisible.” Unfortunately, he came from a small “hick town” and people didn’t believe him. Aristotle, for example, ridiculed him. Because Aristotle was more respected, Democritus’ ideas faded into history.

5. Alchemy • The ancient Greeks were thinkers. They talked the talk but didn’t walk the walk. • The ancient Egyptians, on the other hand, were a practical people and invented a lot of things. They made the first glass, and dyes and medicines, for example.

6. Alchemy • The Greeks called this “chemia,” after the Egyptian word “Chem,” which also meant black. • Chem was the Egyptians’ name for their own country. • Some people thought that chemia meant “black magic,” since some of the processes the Egyptians were using seemed like magic.

7. Alchemy • When the Arabs later conquered Egypt, they added the prefix “al” which means “the.” • So it became “al chemia” • And later in English, it was called alchemy. And that was appropriate because for a while, alchemy was as much phoney-baloney magic as it was real science.

8. An Alchemist at work…(http://en.wikipedia.org/wiki/Alchemy) Paracelsus was a famous alchemist who actually discovered salt in about 1530. Salt had been known for thousands of years, but he realized some of its “properties” and was probably the first person to realize that elements could come together to form compounds, which are totally different from the elements they are made from. Paracelsus also is credited with discovering zinc. The alchemist in the picture may or may not actually be Paracelsus, but it’s a famous painting of one.

9. Robert Boyle: The Last Alchemist and the First Chemist(http://en.wikipedia.org/wiki/Robert_Boyle) A 17th century British nobleman (the youngest of 14 children born to the Earl of Cork). He met Galileo and was an alchemist. Maybe the last of the alchemists and the first one to be a “real” scientist. Boyle invented a vacuum pump, did many experiments on gases, and is credited with “Boyle’s Law.” P1 x V1 = P2 x V2 This law states that pressure and volume are “inversely proportional” to each other; in other words, as pressure goes up, volume goes down, and vice versa.

10. Elements • By 1700, about 14 elements were known. By the end of the 1700’s, around 1783, another 11 were known. • Chemistry was evolving during this time, but few chemists paid attention to the quantitative aspects of chemistry. They observed, but they didn’t measure. • In the late 1700’s a French chemist changed all that. He was Antoine Lavoisier, but first…

11. Phlogiston and Priestly(http://en.wikipedia.org/wiki/Joseph_Priestley) Phlogiston was a theory that explained how things burned and what happened when they did.Today we know it is totally wrong, but “back in the day” it was the accepted explanation. Remember that theories can always be proven wrong if we get better data.

12. Antione Lavoisier(http://www.answers.com/topic/antoine-lavoisier) Father of Modern Chemistry Proved that air was composed of 1/5 oxygen and 4/5 nitrogen Demonstrated experimentally the principle later renamed “The Law of Conservation of Mass.” Proved that hydrogen and oxygen combine to form water, proving at last that water was a compound. Beheaded on 5/2/1794 by guillotine during the French Revolution at age of 50.

13. John Dalton(http://www.intute.ac.uk/sciences/blog/wp-content/uploads/2007/09/johndalton.jpg) A Quaker schoolmaster (became a teacher at the age of 12) who studied all sciences, but made his greatest contributions in chemistry. Developed Atomic Theory and Law of Multiple Proportions. Atomic Theory helped to explain many of the observations that scientists were making. Law of Multiple Proportions helped to explain that 2 elements could combine to form more than 1 compound; for example CO and CO2.

14. Dalton’s Atomic Theory • 1. All elements are composed of tiny indivisible particles called atoms. • 2. Atoms of the same element are identical. The atoms of any one element are different from those of other elements. • 3. Atoms of different elements can chemically combine with one another in small whole-number ratios to form compounds. • 4. Chemical reactions occur when atoms are separated, joined or rearranged. Atoms of one element cannot be changed into atoms of another element by chemical rxns.

15. Indivisible? • Well, Dalton did this work in the early 1800’s. • We know now that atoms are composed of protons, neutrons and electrons. Dalton didn’t know about them—they hadn’t been discovered yet! • HOWEVER, the atom is “the smallest part of an element that retains the properties of that element.” • So an atom of gold is still gold and is different from an atom of carbon.

16. E. Goldstein • German physicist Eugen Goldstein discovered the proton in 1886. • The proton is positively charged and determines the identity of an element. • The number of protons is a property called “atomic number.” Each element has a unique atomic number.

17. JJ Thompson(http://www.manep.ch/img/photo/challenges/nanotubes/thompson.jpg) In 1897, Thompson discovered the electron. Electrons are negatively charged and have almost no mass at all, compared to a proton. Thompson revised Dalton’s model of the atom with one of his own, called the “Plum Pudding Model.”

18. Plum Pudding Model(http://en.wikipedia.org/wiki/Plum_pudding_model) Plum Pudding is a British dessert in which plums are scattered more or less randomly throughout a cake (the pudding). Thompson knew atoms contained electrons, and knew they were negative. He also knew that the atoms overall were neutral. So, he proposed that the electrons were randomly distributed throughout. A little-known fact is that they weren’t just sitting there. In fact, they were moving, and Thompson proposed they were moving more or less in a circular fashion within the positively charged “rest of the atom.”

19. Ernest Rutherford(https://reich-chemistry.wikispaces.com/file/view/Ernest_Rutherford.JPG) The Plum Pudding Model wouldn’t last long, because one of JJ’s former students did some experiments that forced the model to be revised again. Rutherford was from New Zealand, and like his mentor, Thompson, also won a Nobel Prize for his work. His “work” was the famous “gold foil” experiments, where he was researching alpha particles (see Chapter 28 stuff again). As sometimes happened, Rutherford didn’t set out to discover what he actually did.

20. The Gold Foil Experiment(http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/ruther14.swf) Check out the link!(http://www.rsc.org/chemsoc/timeline//pages/1911.html)Reference for below… Rutherford created a device to “shoot” αparticles at a thin piece of gold foil, literally only a few atoms thick. He expected them to go through with little or no deflection. But that’s NOT what happened. Some bounced straight back as if they had hit a brick wall!

21. Shocked, SHOCKED!The Nuclear Model • Rutherford was completely surprised by this result. • He had accidentally discovered the nucleus. • Rutherford said that most of the mass of the atom was contained in a small, dense center which was positively charged. • The electrons still rotated around the nucleus, but most of the atom was composed of “empty space.” • We usually call Rutherford’s model the “nuclear model.”

22. Neils Bohr(http://www.usd.edu/phys/courses/phys300/gallery/clark/bohr.html) Rutherford’s nuclear model only really lasted for about 3 years, before Neils Bohr (who, oh by the way, also won a Nobel Prize for this) revised it again. Bohr asked a question: if the electrons are rotating around the nucleus, why don’t they “run out of energy.” As they did, they would come closer and closer, attracted by the opposite charge of the nucleus, and eventually collapse onto the nucleus, destroying the atom in the process. This doesn’t happen, and Bohr answered why. His model is usually called “the Planetary model,” because in his model, electrons “orbit” the nucleus much as our planets orbit the Sun. Soccer goalie on Denmark’s 1908 Olympic team AND a Nobel Prize winner!!

23. Bohr’s Planetary Model(http://www.rsc.org/chemsoc/timeline//pages/1913.html) But the electrons don’t just orbit anywhere. They actually exist in orbits that Bohr called “energy levels.” Each energy level has a certain amount of energy. Electrons can move to a higher energy level by gaining energy. Or they can drop to a lower energy level by losing (or emitting) energy.

24. Energy Levelshttp://library.thinkquest.org/C006669/media/Chem/img/bohr.gif • An energy level is a “region around the nucleus where an electron is likely to be moving.” • The first energy level (n = 1) has the lowest energy. It is called “the ground state.” • Things in nature prefer to be in the lowest possible energy state.

25. Need for a Better Model • Bohr’s model has some limitations. • It worked very well for hydrogen (the simplest atom with only 1 electron). It allowed scientists to make detailed calculations that explains the behavior of H. • It didn’t work for other elements, mostly because the caluclations were so detailed and complex they couldn’t be done. • It also violated the Heisenberg Uncertainty Principle (but that hadn’t been discovered yet). We’ll get to that.

26. The Modern Model of the Atom • Many scientists (Louis DeBroglie, Max Planck, Albert Einstein, Erwin Schroedinger, and many others) worked on the model of the atom. • Actually, they weren’t working on the model of the atom. They were just working on interesting scientific problems. But they all made contributions to our current understanding of the atom. • Quantum mechanics is the “modern” model of the atom. By the early 1930s, it had been “born.” It’s the model we still use today.

27. Quantum Mechanicshttp://www.hmi.de/bereiche/SF/SF7/PANS/english/nobel/Schroedinger/Schroedinger_01.jpg • When scientists started to use the math techniques that they used with waves, everything started to come together and make total sense. • Erwin Schroedinger finally made the “connection” between deBroglie’s work and Bohr’s work. • He said that electrons weren’t orbiting in certain orbits around the nucleus, but instead described them as being found in “certain geometric forms around the nucleus.” • We’re going to call these areas where we find electrons “atomic orbitals.” His deceptively simple but really complex equation.

28. Heisenberg Uncertainty Principlehttp://www.ostheimer.at/mambo/images/stories/Werner_Heisenberg_Tafel.jpg • The Heisenberg Uncertainty Principle states that for a very small particle, such as an electron, you cannot know both its exact momentum and its exact position at the same time. Since momentum = mass x velocity and since the mass of the electron is known, for all practical purposes, the Heisenberg Uncertainty Principle says that you can’t know both the position of the electron and the speed of the electron, at the same time.

29. The End